// ******************************************************************************
   //
   // Title:       Force Field X.
   // Description: Force Field X - Software for Molecular Biophysics.
   // Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
   //
   // This file is part of Force Field X.
   //
   // Force Field X is free software; you can redistribute it and/or modify it
  // under the terms of the GNU General Public License version 3 as published by
  // the Free Software Foundation.
  //
  // Force Field X is distributed in the hope that it will be useful, but WITHOUT
  // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
  // details.
  //
  // You should have received a copy of the GNU General Public License along with
  // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
  // Place, Suite 330, Boston, MA 02111-1307 USA
  //
  // Linking this library statically or dynamically with other modules is making a
  // combined work based on this library. Thus, the terms and conditions of the
  // GNU General Public License cover the whole combination.
  //
  // As a special exception, the copyright holders of this library give you
  // permission to link this library with independent modules to produce an
  // executable, regardless of the license terms of these independent modules, and
  // to copy and distribute the resulting executable under terms of your choice,
  // provided that you also meet, for each linked independent module, the terms
  // and conditions of the license of that module. An independent module is a
  // module which is not derived from or based on this library. If you modify this
  // library, you may extend this exception to your version of the library, but
  // you are not obligated to do so. If you do not wish to do so, delete this
  // exception statement from your version.
  //
  // ******************************************************************************
  package ffx.potential.parsers;
  
  import ffx.crystal.Crystal;
  import ffx.crystal.SpaceGroup;
  import ffx.crystal.SpaceGroupDefinitions;
  import ffx.crystal.SpaceGroupInfo;
  import ffx.crystal.SymOp;
  import ffx.numerics.math.DoubleMath;
  import ffx.potential.MolecularAssembly;
  import ffx.potential.Utilities.FileType;
  import ffx.potential.bonded.AminoAcidUtils;
  import ffx.potential.bonded.AminoAcidUtils.AminoAcid3;
  import ffx.potential.bonded.Atom;
  import ffx.potential.bonded.Bond;
  import ffx.potential.bonded.MSNode;
  import ffx.potential.bonded.Molecule;
  import ffx.potential.bonded.NucleicAcidUtils;
  import ffx.potential.bonded.Polymer;
  import ffx.potential.bonded.Residue;
  import ffx.potential.parameters.ForceField;
  import ffx.utilities.Hybrid36;
  import ffx.utilities.StringUtils;
  import org.apache.commons.configuration2.CompositeConfiguration;
  
  import java.io.BufferedReader;
  import java.io.BufferedWriter;
  import java.io.File;
  import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.io.FileWriter;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.OptionalDouble;
  import java.util.Set;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  import java.util.stream.Collectors;
  
  import static ffx.potential.bonded.BondedUtils.numberAtoms;
  import static ffx.potential.bonded.NamingUtils.renameAtomsToPDBStandard;
  import static ffx.potential.bonded.PolymerUtils.assignAtomTypes;
  import static ffx.potential.bonded.PolymerUtils.buildDisulfideBonds;
  import static ffx.potential.bonded.PolymerUtils.buildMissingResidues;
  import static ffx.potential.bonded.PolymerUtils.locateDisulfideBonds;
  import static ffx.potential.parsers.PDBFilter.PDBFileStandard.VERSION3_2;
  import static ffx.potential.parsers.PDBFilter.PDBFileStandard.VERSION3_3;
  import static ffx.utilities.StringUtils.padLeft;
  import static java.lang.Double.parseDouble;
  import static java.lang.Integer.parseInt;
  import static java.lang.String.format;
  import static org.apache.commons.lang3.StringUtils.repeat;
  import static org.apache.commons.math3.util.FastMath.min;
  import static org.apache.commons.math3.util.FastMath.toDegrees;
  
  /**
  * The PDBFilter class parses data from a Protein DataBank (*.PDB) file. The following records are
  * recognized: ANISOU, ATOM, CONECT, CRYST1, END, HELIX, HETATM, LINK, SHEET, SSBOND, REMARK. The
  * rest are currently ignored.
  *
  * @author Michael J. Schnieders
  * @see <a href="http://www.wwpdb.org/documentation/format32/v3.2.html">PDB format 3.2</a>
  * @since 1.0
  */
 public final class PDBFilter extends SystemFilter {
 
   private static final Logger logger = Logger.getLogger(PDBFilter.class.getName());
   private static final Set<String> backboneNames;
   private static final Set<String> constantPhBackboneNames;
   private static final Set<String> naBackboneNames;
 
   static {
     String[] names = {"C", "CA", "N", "O", "OXT", "OT2"};
     backboneNames = Set.of(names);
 
     String[] constantPhNames = {"C", "CA", "N", "O", "OXT", "OT2", "H", "HA", "H1", "H2", "H3"};
     constantPhBackboneNames = Set.of(constantPhNames);
 
     String[] naNames = {"P", "OP1", "OP2", "O5'", "C5'", "C4'", "O4'", "C3'", "O3'", "C2'", "C1'"};
     naBackboneNames = Set.of(naNames);
   }
 
   /**
    * Map of SEQRES entries.
    */
   private final Map<Character, String[]> seqRes = new HashMap<>();
   /**
    * Map of DBREF entries.
    */
   private final Map<Character, int[]> dbRef = new HashMap<>();
   /**
    * List of altLoc characters seen in the PDB file.
    */
   private final List<Character> altLocs = new ArrayList<>();
   /**
    * List of segIDs defined for the PDB file.
    *
    * <p>The expectation is for chain naming from A-Z, then from 0-9. For large systems, chain names
    * are sometimes reused due to limitations in the PDB format.
    *
    * <p>However, we define segIDs to always be unique. For the first A-Z,0-9 series chainID ==
    * segID. Then, for second A-Z,0-9 series, the segID = 1A-1Z,10-19, and for the third series segID
    * = 2A-2Z,20-29, and so on.
    */
   private final List<String> segIDs = new ArrayList<>();
 
   private final Map<Character, List<String>> segidMap = new HashMap<>();
   /**
    * Maps a chain to the number of insertion codes encountered in that chain.
    */
   private final Map<Character, Integer> insertionCodeCount = new HashMap<>();
   /**
    * Maps chainIDResNumInsCode to renumbered chainIDResNum. For example, residue 52A in chain C might
    * be renumbered to residue 53, and mapped as "C52A" to "C53".
    */
   private final Map<String, String> pdbToNewResMap = new HashMap<>();
   /**
    * List of modified residues *
    */
   private final Map<String, String> modRes = new HashMap<>();
   /**
    * Keep track of ATOM record serial numbers to match them with ANISOU records.
    */
   private final HashMap<Integer, Atom> atoms = new HashMap<>();
 
   private final Map<MolecularAssembly, BufferedReader> readers = new HashMap<>();
   /**
    * The current altLoc - i.e., the one we are defining a chemical system for.
    */
   private Character currentAltLoc = 'A';
   /**
    * Character for the current chain ID.
    */
   private Character currentChainID = null;
   /**
    * String for the current SegID.
    */
   private String currentSegID = null;
   /**
    * Flag to indicate a mutation is requested.
    */
   private boolean mutate = false;
   private List<Mutation> mutations = null;
   private List<Integer> resNumberList = null;
   /**
    * Flag to indicate if missing fields should be printed (i.e. missing B-factors).
    */
   private boolean printMissingFields = true;
   /**
    * Number of symmetry operators when expanding to a P1 unit cell (-1 saves as current spacegroup).
    */
   private int nSymOp = -1;
   /**
    * Number of replicates in A lattice direction (-1 defaults to unit cell).
    */
   private int lValue = -1;
   /**
    * Number of replicates in B lattice direction (-1 defaults to unit cell).
    */
   private int mValue = -1;
   /**
    * Number of replicates in C lattice direction (-1 defaults to unit cell).
    */
   private int nValue = -1;
   /**
    * The serial field continues from the previous asymmetric unit when expanding to P1. This is not
    * used when saving as the current spacegroup.
    */
   private int serialP1 = 0;
   /**
    * Assume current standard.
    */
   private PDBFileStandard fileStandard = VERSION3_3;
   /**
    * If false, skip logging "Saving file".
    */
   private boolean logWrites = true;
   /**
    * Keep track of the current MODEL in the file.
    */
   private int modelsRead = 1;
   /**
    * Tracks output MODEL numbers. Unused if below zero.
    */
   private int modelsWritten = -1;
   /**
    * Replicates vector dimensions if saving as expanded.
    */
   private int[] lmn = new int[]{1, 1, 1};
 
   private final File readFile;
   private List<String> remarkLines = Collections.emptyList();
   private double lastReadLambda = Double.NaN;
 
   /**
    * If true, read in titratable residues in their fully protonated form.
    */
   private boolean constantPH = false;
   /**
    * If true, read in titratable residues in their protonated form.
    */
   private boolean rotamerTitration = false;
   /**
    * List of residue to rename for constantPH simulations.
    */
   private static final HashMap<AminoAcid3, AminoAcid3> constantPHResidueMap = new HashMap<>();
 
   static {
     // Lysine
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.LYD, AminoAcidUtils.AminoAcid3.LYS);
     // Cysteine
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.CYD, AminoAcidUtils.AminoAcid3.CYS);
     // Histidine
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.HID, AminoAcidUtils.AminoAcid3.HIS);
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.HIE, AminoAcidUtils.AminoAcid3.HIS);
     // Aspartate
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.ASP, AminoAcidUtils.AminoAcid3.ASD);
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.ASH, AminoAcidUtils.AminoAcid3.ASD);
     // Glutamate
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.GLU, AminoAcidUtils.AminoAcid3.GLD);
     constantPHResidueMap.put(AminoAcidUtils.AminoAcid3.GLH, AminoAcidUtils.AminoAcid3.GLD);
   }
 
   /**
    * List of residue to rename for rotamer titration simulations.
    */
   private static final HashMap<AminoAcid3, AminoAcid3> rotamerResidueMap = new HashMap<>();
 
   static {
     // Lysine
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.LYD, AminoAcidUtils.AminoAcid3.LYS);
     // Histidine
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.HID, AminoAcidUtils.AminoAcid3.HIS);
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.HIE, AminoAcidUtils.AminoAcid3.HIS);
     // Aspartate
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.ASP, AminoAcidUtils.AminoAcid3.ASH);
     // Glutamate
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.GLU, AminoAcidUtils.AminoAcid3.GLH);
     //Cysteine
     rotamerResidueMap.put(AminoAcidUtils.AminoAcid3.CYD, AminoAcidUtils.AminoAcid3.CYS);
   }
 
   /**
    * Constructor for PDBFilter.
    *
    * @param files             a {@link java.util.List} object.
    * @param molecularAssembly a {@link ffx.potential.MolecularAssembly} object.
    * @param forceField        a {@link ffx.potential.parameters.ForceField} object.
    * @param properties        a {@link org.apache.commons.configuration2.CompositeConfiguration}
    *                          object.
    */
   public PDBFilter(List<File> files, MolecularAssembly molecularAssembly, ForceField forceField,
                    CompositeConfiguration properties) {
     super(files, molecularAssembly, forceField, properties);
     bondList = new ArrayList<>();
     this.fileType = FileType.PDB;
     readFile = files.getFirst();
   }
 
   /**
    * Parse the PDB File from a URL.
    *
    * @param file              a {@link java.io.File} object.
    * @param molecularAssembly a {@link ffx.potential.MolecularAssembly} object.
    * @param forceField        a {@link ffx.potential.parameters.ForceField} object.
    * @param properties        a {@link org.apache.commons.configuration2.CompositeConfiguration}
    *                          object.
    */
   public PDBFilter(File file, MolecularAssembly molecularAssembly, ForceField forceField,
                    CompositeConfiguration properties) {
     super(file, molecularAssembly, forceField, properties);
     bondList = new ArrayList<>();
     this.fileType = FileType.PDB;
     readFile = file;
   }
 
   /**
    * Parse the PDB File from a URL.
    *
    * @param file                a {@link java.io.File} object.
    * @param molecularAssemblies a {@link java.util.List} object.
    * @param forceField          a {@link ffx.potential.parameters.ForceField} object.
    * @param properties          a {@link org.apache.commons.configuration2.CompositeConfiguration}
    *                            object.
    */
   public PDBFilter(File file, List<MolecularAssembly> molecularAssemblies, ForceField forceField,
                    CompositeConfiguration properties) {
     super(file, molecularAssemblies, forceField, properties);
     bondList = new ArrayList<>();
     this.fileType = FileType.PDB;
     readFile = file;
   }
 
   /**
    * Constructor for PDBFilter with residue numbers.
    *
    * @param file              a {@link java.util.List} object.
    * @param molecularAssembly a {@link ffx.potential.MolecularAssembly} object.
    * @param forceField        a {@link ffx.potential.parameters.ForceField} object.
    * @param properties        a {@link org.apache.commons.configuration2.CompositeConfiguration}
    *                          object.
    * @param resNumberList     a List of integer residue numbers for constant pH rotamer
    *                          optimization.
    */
   public PDBFilter(File file, MolecularAssembly molecularAssembly, ForceField forceField,
                    CompositeConfiguration properties, List<Integer> resNumberList) {
     super(file, molecularAssembly, forceField, properties);
     bondList = new ArrayList<>();
     this.fileType = FileType.PDB;
     this.readFile = file;
     this.resNumberList = resNumberList;
     //this.chainList = chainList;
   }
 
 
   /**
    * Simple method useful for converting files to PDB format.
    *
    * @param atom a {@link ffx.potential.bonded.Atom} object.
    * @return Returns a PDB ATOM or HETATM record for the passed Atom.
    */
   public static String toPDBAtomLine(Atom atom) {
     StringBuilder sb;
     if (atom.isHetero()) {
       sb = new StringBuilder("HETATM");
     } else {
       sb = new StringBuilder("ATOM  ");
     }
     sb.append(repeat(" ", 74));
 
     String name = atom.getName();
     int nameLength = name.length();
     if (nameLength > 4) {
       name = name.substring(0, 4);
     } else if (nameLength == 1) {
       name = name + "  ";
     } else if (nameLength == 2) {
       name = name + " ";
     }
     int serial = atom.getXyzIndex();
     sb.replace(6, 16, format("%5s " + padLeft(name.toUpperCase(), 4), Hybrid36.encode(5, serial)));
 
     Character altLoc = atom.getAltLoc();
     if (altLoc != null) {
       sb.setCharAt(16, altLoc);
     } else {
       char blankChar = ' ';
       sb.setCharAt(16, blankChar);
     }
 
     String resName = atom.getResidueName();
     sb.replace(17, 20, padLeft(resName.toUpperCase(), 3));
 
     char chain = atom.getChainID();
     sb.setCharAt(21, chain);
 
     int resID = atom.getResidueNumber();
     sb.replace(22, 26, format("%4s", Hybrid36.encode(4, resID)));
 
     double[] xyz = atom.getXYZ(null);
     StringBuilder decimals = new StringBuilder();
     for (int i = 0; i < 3; i++) {
       try {
         decimals.append(StringUtils.fwFpDec(xyz[i], 8, 3));
       } catch (IllegalArgumentException ex) {
         String newValue = StringUtils.fwFpTrunc(xyz[i], 8, 3);
         logger.info(format(" XYZ coordinate %8.3f for atom %s overflowed PDB format and is truncated to %s.",
             xyz[i], atom, newValue));
         decimals.append(newValue);
       }
     }
     try {
       decimals.append(StringUtils.fwFpDec(atom.getOccupancy(), 6, 2));
     } catch (IllegalArgumentException ex) {
       logger.severe(format(" Occupancy %6.2f for atom %s must be between 0 and 1.", atom.getOccupancy(), atom));
     }
     try {
       decimals.append(StringUtils.fwFpDec(atom.getTempFactor(), 6, 2));
     } catch (IllegalArgumentException ex) {
       String newValue = StringUtils.fwFpTrunc(atom.getTempFactor(), 6, 2);
       logger.info(
           format(" B-factor %6.2f for atom %s overflowed the PDB format and is truncated to %s.",
               atom.getTempFactor(), atom, newValue));
       decimals.append(newValue);
     }
 
     sb.replace(30, 66, decimals.toString());
     sb.replace(78, 80, format("%2d", 0));
     sb.append("\n");
     return sb.toString();
   }
 
   public void setConstantPH(boolean constantPH) {
     this.constantPH = constantPH;
   }
 
   public void setRotamerTitration(boolean rotamerTitration) {
     this.rotamerTitration = rotamerTitration;
   }
 
   /**
    * clearSegIDs
    */
   public void clearSegIDs() {
     segIDs.clear();
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void closeReader() {
     for (MolecularAssembly system : systems) {
       BufferedReader br = readers.get(system);
       if (br != null) {
         try {
           br.close();
         } catch (IOException ex) {
           logger.warning(format(" Exception in closing system %s: %s", system.toString(), ex));
         }
       }
     }
   }
 
   @Override
   public int countNumModels() {
     Set<File> files = systems.stream().map(MolecularAssembly::getFile).map(File::toString).distinct()
         .map(File::new).collect(Collectors.toSet());
 
     // Dangers of parallelism are minimized by: unique files/filenames, read-only access.
     return files.parallelStream().mapToInt((File fi) -> {
       int nModelsLocal = 0;
       try (BufferedReader br = new BufferedReader(new FileReader(fi))) {
         String line = br.readLine();
         while (line != null) {
           if (line.startsWith("MODEL")) {
             ++nModelsLocal;
           }
           line = br.readLine();
         }
         nModelsLocal = Math.max(1, nModelsLocal);
       } catch (IOException ex) {
         logger.info(format(" Exception in parsing file %s: %s", fi, ex));
       }
       return nModelsLocal;
     }).sum();
   }
 
   /**
    * Get the list of alternate locations encountered.
    *
    * @return the alternate location list.
    */
   public List<Character> getAltLocs() {
     return altLocs;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public OptionalDouble getLastReadLambda() {
     return Double.isNaN(lastReadLambda) ? OptionalDouble.empty() : OptionalDouble.of(lastReadLambda);
   }
 
   /**
    * Returns all the remark lines found by the last readFile call.
    *
    * @return Remark lines from the last readFile call.
    */
   @Override
   public String[] getRemarkLines() {
     int nRemarks = remarkLines.size();
     return remarkLines.toArray(new String[nRemarks]);
   }
 
   @Override
   public int getSnapshot() {
     return modelsRead;
   }
 
   /**
    * Mutate residue(s) as the PDB file is being parsed.
    *
    * @param mutations a {@link java.util.List} object.
    */
   public void mutate(List<Mutation> mutations) {
     mutate = true;
     if (this.mutations == null) {
       this.mutations = new ArrayList<>();
     }
     this.mutations.addAll(mutations);
   }
 
   /**
    * Parse the PDB File
    */
   @Override
   public boolean readFile() {
     remarkLines = new ArrayList<>();
     // First atom is #1, to match xyz file format
     int xyzIndex = 1;
     setFileRead(false);
     systems.add(activeMolecularAssembly);
 
     List<String> conects = new ArrayList<>();
     List<String> links = new ArrayList<>();
     List<String> ssbonds = new ArrayList<>();
     List<String> structs = new ArrayList<>();
     try {
       for (File file : files) {
         currentFile = file;
         if (mutate) {
           List<Character> chainIDs = new ArrayList<>();
           try (BufferedReader br = new BufferedReader(new FileReader(file))) {
             String line = br.readLine();
             while (line != null) {
               // Replace all tabs w/ 4x spaces
               line = line.replaceAll("\t", "    ");
               String identity = line;
               if (line.length() > 6) {
                 identity = line.substring(0, 6);
               }
               identity = identity.trim().toUpperCase();
               Record record;
               try {
                 record = Record.valueOf(identity);
               } catch (Exception e) {
                 // Continue until the record is recognized.
                 line = br.readLine();
                 continue;
               }
               switch (record) {
                 case ANISOU, HETATM, ATOM -> {
                   char c22 = line.charAt(21);
                   boolean idFound = false;
                   for (Character chainID : chainIDs) {
                     if (c22 == chainID) {
                       idFound = true;
                       break;
                     }
                   }
                   if (!idFound) {
                     chainIDs.add(c22);
                   }
                 }
               }
               line = br.readLine();
             }
             for (Mutation mtn : mutations) {
               if (!chainIDs.contains(mtn.chainChar)) {
                 if (chainIDs.size() == 1) {
                   logger.warning(
                       format(" Chain ID %c for mutation not found: only one chain %c found.",
                           mtn.chainChar, chainIDs.getFirst()));
                 } else {
                   logger.warning(
                       format(" Chain ID %c for mutation not found: mutation will not proceed.",
                           mtn.chainChar));
                 }
               }
             }
           } catch (IOException ioException) {
             logger.fine(format(" Exception %s in parsing file to find chain IDs", ioException));
           }
         }
 
         // Check that the current file exists and that we can read it.
         if (currentFile == null || !currentFile.exists() || !currentFile.canRead()) {
           return false;
         }
 
         // Open the current file for parsing.
         try (BufferedReader br = new BufferedReader(new FileReader(currentFile))) {
           // Echo the alternate location being parsed.
           if (currentAltLoc == 'A') {
             logger.info(format(" Reading %s", currentFile.getName()));
           } else {
             logger.info(format(" Reading %s alternate location %s", currentFile.getName(), currentAltLoc));
           }
           activeMolecularAssembly.setAlternateLocation(currentAltLoc);
 
           // Reset the current chain and segID.
           currentChainID = null;
           currentSegID = null;
           boolean containsInsCode = false;
 
           // Read the first line of the file.
           String line = br.readLine();
 
           // Parse until END or ENDMDL is found, or to the end of the file.
           while (line != null) {
             // Replace all tabs w/ 4x spaces
             line = line.replaceAll("\t", "    ");
             String identity = line;
             if (line.length() > 6) {
               identity = line.substring(0, 6);
             }
             identity = identity.trim().toUpperCase();
             Record record;
             try {
               record = Record.valueOf(identity);
             } catch (Exception e) {
               // Continue until the record is recognized.
               line = br.readLine();
               continue;
             }
 
             // Switch on the known record.
             switch (record) {
               case ENDMDL:
               case END: {
                 // Setting "line" to null will exit the loop.
                 line = null;
                 continue;
               }
               case DBREF: {
 // =============================================================================
 //  1 -  6       Record name   "DBREF "
 //  8 - 11       IDcode        idCode             ID code of this entry.
 // 13            Character     chainID            Chain identifier.
 // 15 - 18       Integer       seqBegin           Initial sequence number of the
 //                                                PDB sequence segment.
 // 19            AChar         insertBegin        Initial insertion code of the
 //                                                PDB sequence segment.
 // 21 - 24       Integer       seqEnd             Ending sequence number of the
 //                                                PDB sequence segment.
 // 25            AChar         insertEnd          Ending insertion code of the
 //                                                PDB sequence segment.
 // 27 - 32       LString       database           Sequence database name.
 // 34 - 41       LString       dbAccession        Sequence database accession code.
 // 43 - 54       LString       dbIdCode           Sequence  database identification code.
 // 56 - 60       Integer       dbseqBegin         Initial sequence number of the
 //                                                database seqment.
 // 61            AChar         idbnsBeg           Insertion code of initial residue of the
 //                                                segment, if PDB is the reference.
 // 63 - 67       Integer       dbseqEnd           Ending sequence number of the
 //                                                database segment.
 // 68            AChar         dbinsEnd           Insertion code of the ending residue of
 //                                                the segment, if PDB is the reference.
 // =============================================================================
                 Character chainID = line.substring(12, 13).toUpperCase().charAt(0);
                 int seqBegin = parseInt(line.substring(14, 18).trim());
                 int seqEnd = parseInt(line.substring(20, 24).trim());
                 int[] seqRange = dbRef.computeIfAbsent(chainID, k -> new int[2]);
                 seqRange[0] = seqBegin;
                 seqRange[1] = seqEnd;
                 break;
               }
               case SEQRES: {
 // =============================================================================
 //  1 -  6        Record name    "SEQRES"
 //  8 - 10        Integer        serNum       Serial number of the SEQRES record for the
 //                                            current  chain. Starts at 1 and increments
 //                                            by one  each line. Reset to 1 for each chain.
 // 12             Character      chainID      Chain identifier. This may be any single
 //                                            legal  character, including a blank which is
 //                                            is used if there is only one chain.
 // 14 - 17        Integer        numRes       Number of residues in the chain.
 //                                            This  value is repeated on every record.
 // 20 - 22        Residue name   resName      Residue name.
 // 24 - 26        Residue name   resName      Residue name.
 // 28 - 30        Residue name   resName      Residue name.
 // 32 - 34        Residue name   resName      Residue name.
 // 36 - 38        Residue name   resName      Residue name.
 // 40 - 42        Residue name   resName      Residue name.
 // 44 - 46        Residue name   resName      Residue name.
 // 48 - 50        Residue name   resName      Residue name.
 // 52 - 54        Residue name   resName      Residue name.
 // 56 - 58        Residue name   resName      Residue name.
 // 60 - 62        Residue name   resName      Residue name.
 // 64 - 66        Residue name   resName      Residue name.
 // 68 - 70        Residue name   resName      Residue name.
 // =============================================================================
                 activeMolecularAssembly.addHeaderLine(line);
                 Character chainID = line.substring(11, 12).toUpperCase().charAt(0);
                 int serNum = parseInt(line.substring(7, 10).trim());
                 String[] chain = seqRes.get(chainID);
                 int numRes = parseInt(line.substring(13, 17).trim());
                 if (chain == null) {
                   chain = new String[numRes];
                   seqRes.put(chainID, chain);
                 }
                 int resID = (serNum - 1) * 13;
                 int end = line.length();
                 for (int start = 19; start + 3 <= end; start += 4) {
                   String res = line.substring(start, start + 3).trim();
                   if (res.isEmpty()) {
                     break;
                   }
                   chain[resID++] = res;
                 }
                 break;
               }
               case MODRES: {
 // =============================================================================
 //  1 -  6        Record name     "MODRES"
 //  8 - 11        IDcode          idCode         ID code of this entry.
 // 13 - 15        Residue name    resName        Residue name used in this entry.
 // 17             Character       chainID        Chain identifier.
 // 19 - 22        Integer         seqNum         Sequence number.
 // 23             AChar           iCode          Insertion code.
 // 25 - 27        Residue name    stdRes         Standard residue name.
 // 30 - 70        String          comment        Description of the residue modification.
 // =============================================================================
                 String modResName = line.substring(12, 15).trim();
                 String stdName = line.substring(24, 27).trim();
                 modRes.put(modResName.toUpperCase(), stdName.toUpperCase());
                 activeMolecularAssembly.addHeaderLine(line);
                 break;
               }
               case ANISOU: {
 // =============================================================================
 //  1 - 6        Record name   "ANISOU"
 //  7 - 11       Integer       serial         Atom serial number.
 // 13 - 16       Atom          name           Atom name.
 // 17            Character     altLoc         Alternate location indicator
 // 18 - 20       Residue name  resName        Residue name.
 // 22            Character     chainID        Chain identifier.
 // 23 - 26       Integer       resSeq         Residue sequence number.
 // 27            AChar         iCode          Insertion code.
 // 29 - 35       Integer       u[0][0]        U(1,1)
 // 36 - 42       Integer       u[1][1]        U(2,2)
 // 43 - 49       Integer       u[2][2]        U(3,3)
 // 50 - 56       Integer       u[0][1]        U(1,2)
 // 57 - 63       Integer       u[0][2]        U(1,3)
 // 64 - 70       Integer       u[1][2]        U(2,3)
 // 77 - 78       LString(2)    element        Element symbol, right-justified.
 // 79 - 80       LString(2)    charge         Charge on the atom.
 // =============================================================================
                 boolean deleteAnisou = properties.getBoolean("delete-anisou", false);
                 double resetBfactors = properties.getDouble("reset-bfactors", -1.0);
                 if (deleteAnisou || resetBfactors >= 0.0) {
                   break;
                 }
                 Integer serial = Hybrid36.decode(5, line.substring(6, 11));
                 Character altLoc = line.substring(16, 17).toUpperCase().charAt(0);
                 if (!altLocs.contains(altLoc)) {
                   altLocs.add(altLoc);
                 }
                 if (!altLoc.equals(' ') && !altLoc.equals('A') && !altLoc.equals(currentAltLoc)) {
                   break;
                 }
                 double[] adp = new double[6];
                 adp[0] = parseInt(line.substring(28, 35).trim()) * 1.0e-4;
                 adp[1] = parseInt(line.substring(35, 42).trim()) * 1.0e-4;
                 adp[2] = parseInt(line.substring(42, 49).trim()) * 1.0e-4;
                 adp[3] = parseInt(line.substring(49, 56).trim()) * 1.0e-4;
                 adp[4] = parseInt(line.substring(56, 63).trim()) * 1.0e-4;
                 adp[5] = parseInt(line.substring(63, 70).trim()) * 1.0e-4;
                 if (atoms.containsKey(serial)) {
                   Atom a = atoms.get(serial);
                   a.setAltLoc(altLoc);
                   a.setAnisou(adp);
                 } else {
                   logger.info(format(" No ATOM record for ANISOU serial number %d has been found.", serial));
                   logger.info(format(" This ANISOU record will be ignored:\n %s", line));
                 }
                 break;
               }
               case ATOM: {
 // =============================================================================
 //  1 -  6        Record name   "ATOM  "
 //  7 - 11        Integer       serial       Atom serial number.
 // 13 - 16        Atom          name         Atom name.
 // 17             Character     altLoc       Alternate location indicator.
 // 18 - 20        Residue name  resName      Residue name.
 // 22             Character     chainID      Chain identifier.
 // 23 - 26        Integer       resSeq       Residue sequence number.
 // 27             AChar         iCode        Code for insertion of residues.
 // 31 - 38        Real(8.3)     x            Orthogonal coordinates for X in Angstroms.
 // 39 - 46        Real(8.3)     y            Orthogonal coordinates for Y in Angstroms.
 // 47 - 54        Real(8.3)     z            Orthogonal coordinates for Z in Angstroms.
 // 55 - 60        Real(6.2)     occupancy    Occupancy.
 // 61 - 66        Real(6.2)     tempFactor   Temperature factor.
 // 77 - 78        LString(2)    element      Element symbol, right-justified.
 // 79 - 80        LString(2)    charge       Charge  on the atom.
 // =============================================================================
                 // If it's a misnamed water, it will fall through to HETATM.
                 Integer serial = Hybrid36.decode(5, line.substring(6, 11));
                 String name = line.substring(12, 16).trim();
                 if (name.toUpperCase().contains("1H") || name.toUpperCase().contains("2H")
                     || name.toUpperCase().contains("3H")) {
                   // VERSION3_2 is presently just a placeholder for "anything non-standard".
                   fileStandard = VERSION3_2;
                 }
                 Character altLoc = line.substring(16, 17).toUpperCase().charAt(0);
                 if (!altLocs.contains(altLoc)) {
                   altLocs.add(altLoc);
                 }
 
                 if (!altLoc.equals(' ') && !altLoc.equals('A') && !altLoc.equals(currentAltLoc)) {
                   break;
                 }
 
                 String resName = line.substring(17, 20).trim();
                 Character chainID = line.substring(21, 22).charAt(0);
                 String segID = getSegID(chainID);
                 int resSeq = Hybrid36.decode(4, line.substring(22, 26));
 
                 char insertionCode = line.charAt(26);
                 if (insertionCode != ' ' && !containsInsCode) {
                   containsInsCode = true;
                   logger.warning(
                       " FFX support for files with " + "insertion codes is experimental. "
                           + "Residues will be renumbered to " + "eliminate insertion codes (52A "
                           + "becomes 53, 53 becomes 54, etc)");
                 }
 
                 int offset = insertionCodeCount.getOrDefault(chainID, 0);
                 String pdbResNum = format("%c%d%c", chainID, resSeq, insertionCode);
                 if (!pdbToNewResMap.containsKey(pdbResNum)) {
                   if (insertionCode != ' ') {
                     ++offset;
                     insertionCodeCount.put(chainID, offset);
                   }
                   resSeq += offset;
                   if (offset != 0) {
                     logger.info(
                         format(" Chain %c " + "residue %s-%s renumbered to %c %s-%d", chainID,
                             pdbResNum.substring(1).trim(), resName, chainID, resName, resSeq));
                   }
                   String newNum = format("%c%d", chainID, resSeq);
                   pdbToNewResMap.put(pdbResNum, newNum);
                 } else {
                   resSeq += offset;
                 }
 
                 boolean printAtom = false;
                 if (mutate) {
                   boolean doBreak = false;
                   for (Mutation mtn : mutations) {
                     if (chainID == mtn.chainChar && resSeq == mtn.resID) {
                       mtn.origResName = resName;
                       resName = mtn.resName;
                       String atomName = name.toUpperCase();
 
                       int isAA = AminoAcidUtils.getAminoAcidNumber(resName);
                       int isNA = NucleicAcidUtils.getNucleicAcidNumber(resName);
 
                       if ((isNA != -1 && naBackboneNames.contains(atomName)) || (isAA != -1 && backboneNames.contains(atomName))) {
                         printAtom = true;
                       } else {
                         // grab pur-pur or pyr-pyr alchem. atoms
                         ArrayList<String> alchAtoms = mtn.getAlchemicalAtoms(false);
                         if (alchAtoms == null) {
                           // test to see if atom is involved in glycosyl torsion and if needs renaming (pyr-pur/pur-pyr)
                           String newName = mtn.isNonAlchemicalAtom(atomName);
                           if (newName != null) { // if not null -- use name it
                             printAtom = true;
                             if (newName.startsWith("~")) { // switch from purine to pyrmidine or v.v.
                               // switch name and include it as an alchemical atom
                               name = newName.substring(1);
                               logger.info(format(" DELETING atom %d %s of %s %d in chain %s", serial, atomName, resName, resSeq, chainID));
                             } else {
                               // replace name but do not include as an alchemical atom
                               name = newName;
                             }
                             doBreak = false;
                           } else if (!atomName.contains("'")) {
                             logger.info(format(" DELETING atom %d %s of %s %d in chain %s", serial, atomName, resName, resSeq, chainID));
                             doBreak = true;
                           } else {
                             printAtom = true;
                             doBreak = false;
                           }
                         } else {
                           if (alchAtoms.contains(atomName) && !atomName.contains("'")) {
                             logger.info(format(" DELETING atom %d %s of %s %d in chain %s", serial, atomName, resName, resSeq, chainID));
                             doBreak = true;
                           } else {
                             printAtom = true;
                             doBreak = false;
                           }
                         }
                         break;
                       }
                     }
                   }
                   if (doBreak) {
                     break;
                   }
                 }
 
                 if (constantPH) {
                   AminoAcid3 aa3 = AminoAcidUtils.getAminoAcid(resName.toUpperCase());
                   if (constantPHResidueMap.containsKey(aa3)) {
                     String atomName = name.toUpperCase();
                     AminoAcid3 aa3PH = constantPHResidueMap.get(aa3);
                     resName = aa3PH.name();
                     if (constantPhBackboneNames.contains(atomName)) {
                       logger.info(format(" %s-%d %s", resName, resSeq, atomName));
                     } else if (!atomName.startsWith("H")) {
                       logger.info(format(" %s-%d %s", resName, resSeq, atomName));
                     } else {
                       logger.info(format(" %s-%d %s skipped", resName, resSeq, atomName));
                       break;
                     }
                   }
                 } else if (rotamerTitration) {
                   AminoAcid3 aa3 = AminoAcidUtils.getAminoAcid(resName.toUpperCase());
                   if (rotamerResidueMap.containsKey(aa3) && resNumberList.contains(resSeq)) {
                     AminoAcid3 aa3rotamer = rotamerResidueMap.get(aa3);
                     resName = aa3rotamer.name();
                   }
                 }
                 double[] d = new double[3];
                 d[0] = parseDouble(line.substring(30, 38).trim());
                 d[1] = parseDouble(line.substring(38, 46).trim());
                 d[2] = parseDouble(line.substring(46, 54).trim());
                 double occupancy = 1.0;
                 double tempFactor = 1.0;
                 try {
                   occupancy = parseDouble(line.substring(54, 60).trim());
                   tempFactor = parseDouble(line.substring(60, 66).trim());
                 } catch (NumberFormatException | StringIndexOutOfBoundsException e) {
                   // Use default values.
                   if (printMissingFields) {
                     logger.info(" Missing occupancy and b-factors set to 1.0.");
                     printMissingFields = false;
                   } else if (logger.isLoggable(Level.FINE)) {
                     logger.fine(" Missing occupancy and b-factors set to 1.0.");
                   }
                 }
 
                 double bfactor = properties.getDouble("reset-bfactors", -1.0);
                 if (bfactor >= 0.0) {
                   tempFactor = bfactor;
                 }
 
                 Atom newAtom = new Atom(0, name, altLoc, d, resName, resSeq, chainID, occupancy, tempFactor, segID);
 
                 // Check if this is a modified residue.
                 if (modRes.containsKey(resName.toUpperCase())) {
                   newAtom.setModRes(true);
                 }
                 Atom returnedAtom = (Atom) activeMolecularAssembly.addMSNode(newAtom);
                 if (returnedAtom != newAtom) {
                   // A previously added atom has been retained.
                   atoms.put(serial, returnedAtom);
                   if (logger.isLoggable(Level.FINE)) {
                     logger.fine(returnedAtom + " has been retained over\n" + newAtom);
                   }
                 } else {
                   // The new atom has been added.
                   atoms.put(serial, newAtom);
                   // Check if the newAtom took the xyzIndex of a previous alternate conformer.
                   if (newAtom.getIndex() == 0) {
                     newAtom.setXyzIndex(xyzIndex++);
                   }
                   if (printAtom) {
                     logger.info(newAtom.toString());
                   }
                 }
                 break;
               }
               case HETATM: {
 // =============================================================================
 //  1 - 6        Record name    "HETATM"
 //  7 - 11       Integer        serial        Atom serial number.
 // 13 - 16       Atom           name          Atom name.
 // 17            Character      altLoc        Alternate location indicator.
 // 18 - 20       Residue name   resName       Residue name.
 // 22            Character      chainID       Chain identifier.
 // 23 - 26       Integer        resSeq        Residue sequence number.
 // 27            AChar          iCode         Code for insertion of residues.
 // 31 - 38       Real(8.3)      x             Orthogonal coordinates for X.
 // 39 - 46       Real(8.3)      y             Orthogonal coordinates for Y.
 // 47 - 54       Real(8.3)      z             Orthogonal coordinates for Z.
 // 55 - 60       Real(6.2)      occupancy     Occupancy.
 // 61 - 66       Real(6.2)      tempFactor    Temperature factor.
 // 77 - 78       LString(2)     element       Element symbol; right-justified.
 // 79 - 80       LString(2)     charge        Charge on the atom.
 // =============================================================================
                 Integer serial = Hybrid36.decode(5, line.substring(6, 11));
                 String name = line.substring(12, 16).trim();
                 Character altLoc = line.substring(16, 17).toUpperCase().charAt(0);
                 if (!altLocs.contains(altLoc)) {
                   altLocs.add(altLoc);
                 }
                 if (!altLoc.equals(' ') && !altLoc.equals(currentAltLoc)) {
                   break;
                 }
                 // if (!altLoc.equals(' ') && !altLoc.equals('A') && !altLoc.equals(currentAltLoc)) {
                 //  break;
                 //}
                 String resName = line.substring(17, 20).trim();
                 Character chainID = line.substring(21, 22).charAt(0);
                 String segID = getSegID(chainID);
                 int resSeq = Hybrid36.decode(4, line.substring(22, 26));
 
                 char insertionCode = line.charAt(26);
                 if (insertionCode != ' ' && !containsInsCode) {
                   containsInsCode = true;
                   logger.warning(" FFX support for files with " + "insertion codes is experimental. "
                       + "Residues will be renumbered to " + "eliminate insertion codes (52A "
                       + "becomes 53, 53 becomes 54, etc)");
                 }
 
                 int offset = insertionCodeCount.getOrDefault(chainID, 0);
                 String pdbResNum = format("%c%d%c", chainID, resSeq, insertionCode);
                 if (!pdbToNewResMap.containsKey(pdbResNum)) {
                   if (insertionCode != ' ') {
                     ++offset;
                     insertionCodeCount.put(chainID, offset);
                   }
                   resSeq += offset;
                   if (offset != 0) {
                     logger.info(
                         format(" Chain %c " + "molecule %s-%s renumbered to %c %s-%d", chainID,
                             pdbResNum.substring(1).trim(), resName, chainID, resName, resSeq));
                   }
                   String newNum = format("%c%d", chainID, resSeq);
                   pdbToNewResMap.put(pdbResNum, newNum);
                 } else {
                   resSeq += offset;
                 }
 
                 double[] d = new double[3];
                 d[0] = parseDouble(line.substring(30, 38).trim());
                 d[1] = parseDouble(line.substring(38, 46).trim());
                 d[2] = parseDouble(line.substring(46, 54).trim());
                 double occupancy = 1.0;
                 double tempFactor = 1.0;
                 try {
                   occupancy = parseDouble(line.substring(54, 60).trim());
                   tempFactor = parseDouble(line.substring(60, 66).trim());
                 } catch (NumberFormatException | StringIndexOutOfBoundsException e) {
                   // Use default values.
                   if (printMissingFields) {
                     logger.info(" Missing occupancy and b-factors set to 1.0.");
                     printMissingFields = false;
                   } else if (logger.isLoggable(Level.FINE)) {
                     logger.fine(" Missing occupancy and b-factors set to 1.0.");
                   }
                 }
 
                 double bfactor = properties.getDouble("reset-bfactors", -1.0);
                 if (bfactor >= 0.0) {
                   tempFactor = bfactor;
                 }
 
                 Atom newAtom = new Atom(0, name, altLoc, d, resName, resSeq, chainID, occupancy, tempFactor, segID);
                 newAtom.setHetero(true);
                 // Check if this is a modified residue.
                 if (modRes.containsKey(resName.toUpperCase())) {
                   newAtom.setModRes(true);
                 }
                 Atom returnedAtom = (Atom) activeMolecularAssembly.addMSNode(newAtom);
                 if (returnedAtom != newAtom) {
                   // A previously added atom has been retained.
                   atoms.put(serial, returnedAtom);
                   if (logger.isLoggable(Level.FINE)) {
                     logger.fine(returnedAtom + " has been retained over\n" + newAtom);
                   }
                 } else {
                   // The new atom has been added.
                   atoms.put(serial, newAtom);
                   newAtom.setXyzIndex(xyzIndex++);
                 }
                 break;
               }
               case CRYST1: {
 // =============================================================================
 // The CRYST1 record presents the unit cell parameters, space group, and Z
 // value. If the structure was not determined by crystallographic means, CRYST1
 // simply provides the unitary values, with an appropriate REMARK.
 //
 //  7 - 15       Real(9.3)     a              a (Angstroms).
 // 16 - 24       Real(9.3)     b              b (Angstroms).
 // 25 - 33       Real(9.3)     c              c (Angstroms).
 // 34 - 40       Real(7.2)     alpha          alpha (degrees).
 // 41 - 47       Real(7.2)     beta           beta (degrees).
 // 48 - 54       Real(7.2)     gamma          gamma (degrees).
 // 56 - 66       LString       sGroup         Space  group.
 // 67 - 70       Integer       z              Z value.
 // =============================================================================
                 if (line.length() < 55) {
                   logger.severe(" CRYST1 record is improperly formatted.");
                 }
                 double aaxis = parseDouble(line.substring(6, 15).trim());
                 double baxis = parseDouble(line.substring(15, 24).trim());
                 double caxis = parseDouble(line.substring(24, 33).trim());
                 double alpha = parseDouble(line.substring(33, 40).trim());
                 double beta = parseDouble(line.substring(40, 47).trim());
                 double gamma = parseDouble(line.substring(47, 54).trim());
                 int limit = min(line.length(), 66);
                 String sg = line.substring(55, limit).trim();
                 properties.addProperty("a-axis", aaxis);
                 properties.addProperty("b-axis", baxis);
                 properties.addProperty("c-axis", caxis);
                 properties.addProperty("alpha", alpha);
                 properties.addProperty("beta", beta);
                 properties.addProperty("gamma", gamma);
                 properties.addProperty("spacegroup", SpaceGroupInfo.pdb2ShortName(sg));
                 break;
               }
               case CONECT: {
 // =============================================================================
 //  7 - 11        Integer        serial       Atom  serial number
 // 12 - 16        Integer        serial       Serial number of bonded atom
 // 17 - 21        Integer        serial       Serial number of bonded atom
 // 22 - 26        Integer        serial       Serial number of bonded atom
 // 27 - 31        Integer        serial       Serial number of bonded atom
 //
 // CONECT records involving atoms for which the coordinates are not present
 // in the entry (e.g., symmetry-generated) are not given.
 // CONECT records involving atoms for which the coordinates are missing due
 // to disorder, are also not provided.
 // =============================================================================
                 conects.add(line);
                 break;
               }
               case LINK: {
 // =============================================================================
 // The LINK records specify connectivity between residues that is not implied by
 // the primary structure. Connectivity is expressed in terms of the atom names.
 // They also include the distance associated with each linkage following the
 // symmetry operations at the end of each record.
 // 13 - 16         Atom           name1           Atom name.
 // 17              Character      altLoc1         Alternate location indicator.
 // 18 - 20         Residue name   resName1        Residue  name.
 // 22              Character      chainID1        Chain identifier.
 // 23 - 26         Integer        resSeq1         Residue sequence number.
 // 27              AChar          iCode1          Insertion code.
 // 43 - 46         Atom           name2           Atom name.
 // 47              Character      altLoc2         Alternate location indicator.
 // 48 - 50         Residue name   resName2        Residue name.
 // 52              Character      chainID2        Chain identifier.
 // 53 - 56         Integer        resSeq2         Residue sequence number.
 // 57              AChar          iCode2          Insertion code.
 // 60 - 65         SymOP          sym1            Symmetry operator atom 1.
 // 67 - 72         SymOP          sym2            Symmetry operator atom 2.
 // 74 – 78         Real(5.2)      Length          Link distance
 // =============================================================================
                 char a1 = line.charAt(16);
                 char a2 = line.charAt(46);
                 if (a1 != a2) {
                   // logger.info(format(" Ignoring LINK record as alternate locations do not match\n
                   // %s.", line));
                   break;
                 }
                 if (currentAltLoc == 'A') {
                   if ((a1 == ' ' || a1 == 'A') && (a2 == ' ' || a2 == 'A')) {
                     links.add(line);
                   }
                 } else if (a1 == currentAltLoc && a2 == currentAltLoc) {
                   links.add(line);
                 }
                 break;
               }
               case SSBOND: {
 // =============================================================================
 // The SSBOND record identifies each disulfide bond in protein and polypeptide
 // structures by identifying the two residues involved in the bond.
 // The disulfide bond distance is included after the symmetry operations at
 // the end of the SSBOND record.
 //
 //  8 - 10        Integer         serNum       Serial number.
 // 12 - 14        LString(3)      "CYS"        Residue name.
 // 16             Character       chainID1     Chain identifier.
 // 18 - 21        Integer         seqNum1      Residue sequence number.
 // 22             AChar           icode1       Insertion code.
 // 26 - 28        LString(3)      "CYS"        Residue name.
 // 30             Character       chainID2     Chain identifier.
 // 32 - 35        Integer         seqNum2      Residue sequence number.
 // 36             AChar           icode2       Insertion code.
 // 60 - 65        SymOP           sym1         Symmetry oper for 1st resid
 // 67 - 72        SymOP           sym2         Symmetry oper for 2nd resid
 // 74 – 78        Real(5.2)      Length        Disulfide bond distance
 //
 // If SG of cysteine is disordered then there are possible alternate linkages.
 // wwPDB practice is to put together all possible SSBOND records. This is
 // problematic because the alternate location identifier is not specified in
 // the SSBOND record.
 //
 // Notes:
 // SSBOND records may be invalid if chain IDs are reused.
 // SSBOND records are applied by FFX to all conformers.
 // =============================================================================
                 ssbonds.add(line);
                 break;
               }
               case HELIX: {
 // =============================================================================
 // HELIX records are used to identify the position of helices in the molecule.
 // Helices are named, numbered, and classified by type. The residues where the
 // helix begins and ends are noted, as well as the total length.
 //
 //  8 - 10        Integer        serNum        Serial number of the helix. This starts
 //                                             at 1  and increases incrementally.
 // 12 - 14        LString(3)     helixID       Helix  identifier. In addition to a serial
 //                                             number, each helix is given an
 //                                             alphanumeric character helix identifier.
 // 16 - 18        Residue name   initResName   Name of the initial residue.
 // 20             Character      initChainID   Chain identifier for the chain containing
 //                                             this  helix.
 // 22 - 25        Integer        initSeqNum    Sequence number of the initial residue.
 // 26             AChar          initICode     Insertion code of the initial residue.
 // 28 - 30        Residue  name  endResName    Name of the terminal residue of the helix.
 // 32             Character      endChainID    Chain identifier for the chain containing
 //                                             this  helix.
 // 34 - 37        Integer        endSeqNum     Sequence number of the terminal residue.
 // 38             AChar          endICode      Insertion code of the terminal residue.
 // 39 - 40        Integer        helixClass    Helix class (see below).
 // 41 - 70        String         comment       Comment about this helix.
 // 72 - 76        Integer        length        Length of this helix.
 //
 //                                      CLASS NUMBER
 // TYPE OF  HELIX                     (COLUMNS 39 - 40)
 // --------------------------------------------------------------
 // Right-handed alpha (default)                1
 // Right-handed omega                          2
 // Right-handed pi                             3
 // Right-handed gamma                          4
 // Right-handed 3 - 10                         5
 // Left-handed alpha                           6
 // Left-handed omega                           7
 // Left-handed gamma                           8
 // 2 - 7 ribbon/helix                          9
 // Polyproline                                10
 // =============================================================================
               }
               case SHEET: {
 // =============================================================================
 // SHEET records are used to identify the position of sheets in the molecule.
 // Sheets are both named and numbered. The residues where the sheet begins and
 // ends are noted.
 //
 //  8 - 10        Integer       strand         Strand  number which starts at 1 for each
 //                                             strand within a sheet and increases by one.
 // 12 - 14        LString(3)    sheetID        Sheet  identifier.
 // 15 - 16        Integer       numStrands     Number  of strands in sheet.
 // 18 - 20        Residue name  initResName    Residue  name of initial residue.
 // 22             Character     initChainID    Chain identifier of initial residue in strand.
 // 23 - 26        Integer       initSeqNum     Sequence number of initial residue in strand.
 // 27             AChar         initICode      Insertion code of initial residue in  strand.
 // 29 - 31        Residue name  endResName     Residue name of terminal residue.
 // 33             Character     endChainID     Chain identifier of terminal residue.
 // 34 - 37        Integer       endSeqNum      Sequence number of terminal residue.
 // 38             AChar         endICode       Insertion code of terminal residue.
 // 39 - 40        Integer       sense          Sense of strand with respect to previous
 //                                             strand in the sheet. 0 if first strand,
 //                                             1 if  parallel,and -1 if anti-parallel.
 // 42 - 45        Atom          curAtom        Registration.  Atom name in current strand.
 // 46 - 48        Residue name  curResName     Registration.  Residue name in current strand
 // 50             Character     curChainId     Registration. Chain identifier in current strand.
 // 51 - 54        Integer       curResSeq      Registration.  Residue sequence number
 //                                             in current strand.
 // 55             AChar         curICode       Registration. Insertion code in current strand.
 // 57 - 60        Atom          prevAtom       Registration.  Atom name in previous strand.
 // 61 - 63        Residue name  prevResName    Registration.  Residue name in previous strand.
 // 65             Character     prevChainId    Registration.  Chain identifier in previous strand.
 // 66 - 69        Integer       prevResSeq     Registration. Residue sequence number
 //                                             in previous strand.
 // 70             AChar         prevICode      Registration.  Insertion code in
 //                                             previous strand.
 // =============================================================================
                 structs.add(line);
                 break;
               }
               case MODEL: // Currently, no handling in initial read.
                 break;
               case MTRIX1: {
 // ================================================================================
 // MTRIXn (n = 1, 2, or 3) records present transformations expressing
 // non-crystallographic symmetry.
 // MTRIXn will appear only when such transformations are required to generate an
 // entire asymmetric unit,
 // such as a large viral structure.
 //
 //  8 - 10        Integer       serial         Serial number.
 // 11 - 20        Real(10.6)    m[n][1]        Mn1
 // 21 - 30        Real(10.6)    m[n][2]        Mn2
 // 31 - 40        Real(10.6)    m[n][3]        Mn3
 // 21 - 30        Real(10.6)    v[n]           Vn
 // 60             Integer       iGiven         1 if coordinates for the representations which are
 //                                              approximately related by the transformations of the
 //                                              molecule are contained in the entry. Otherwise, blank.
 // =================================================================================
                 StringBuilder MTRX1 = new StringBuilder(line.substring(11, 55));
                 properties.addProperty("MTRIX1", MTRX1);
                 break;
               }
               case MTRIX2: {
                 StringBuilder MTRX2 = new StringBuilder(line.substring(11, 55));
                 properties.addProperty("MTRIX2", MTRX2);
                 break;
               }
               case MTRIX3: {
                 StringBuilder MTRX3 = new StringBuilder(line.substring(11, 55));
                 properties.addProperty("MTRIX3", MTRX3);
                 break;
               }
               case REMARK: {
                 remarkLines.add(line.trim());
                 if (line.contains("Lambda:")) {
                   Matcher m = lambdaPattern.matcher(line);
                   if (m.find()) {
                     lastReadLambda = Double.parseDouble(m.group(1));
                   }
                 }
 // =================================================================================
 // REMARK 350: presents all transformations, both crystallographic and non-crystallographic,
 // needed to generate the biomolecule. These transformations operate on the coordinates in the
 // entry. Both author and computational descriptions of assemblies are provided, if applicable.
 // For strict ncs case where more than one assembly presents in asymmetric unit, only one
 // chain with unit matrix will reported in REMARK 350, the other chain will be generated
 // by rotation and translation.
 //
 // 20 - 23        Integer       serial         Serial number.
 // 24 - 33        Real(10.6)    m[n][1]        Mn1
 // 34 - 43        Real(10.6)    m[n][2]        Mn2
 // 44 - 53        Real(10.6)    m[n][3]        Mn3
 // 59 - 68        Real(10.6)    v[n]           Vn
 // =================================================================================
                 if (line.length() >= 68) {
                   String remarkType = line.substring(7, 10).trim();
                   if (remarkType.matches("\\d+") && parseInt(remarkType) == 350 && line.substring(13,
                       18).equalsIgnoreCase("BIOMT")) {
                     properties.addProperty("BIOMTn", new StringBuilder(line.substring(24, 68)));
                   }
                 }
                 break;
               }
               default:
                 break;
             }
             line = br.readLine();
           }
 
         } catch (FileNotFoundException fileNotFoundException) {
           logger.log(Level.SEVERE, " PDB file not found", fileNotFoundException);
         }
       }
       xyzIndex--;
       setFileRead(true);
     } catch (IOException e) {
       logger.exiting(PDBFilter.class.getName(), "readFile", e);
       return false;
     }
 
     // Locate disulfide bonds; bond parameters are assigned below.
     List<Bond> ssBondList = locateDisulfideBonds(ssbonds, activeMolecularAssembly, pdbToNewResMap);
 
     // Record the number of atoms read in from the PDB file before applying
     // algorithms that may build new atoms.
     int pdbAtoms = activeMolecularAssembly.getAtomArray().length;
 
     // Remove hydrogen atoms that are not consistent with amino acid residue protonation states (e.g., HIE & HID).
     removeInappropriateHydrogen();
 
     // Build missing backbone atoms in loops.
     buildMissingResidues(xyzIndex, activeMolecularAssembly, seqRes, dbRef);
 
     // Assign atom types. Missing side-chains atoms and missing hydrogen will be built in.
     bondList = assignAtomTypes(activeMolecularAssembly, fileStandard);
 
     // Assign disulfide bonds parameters and log their creation.
     buildDisulfideBonds(ssBondList, activeMolecularAssembly, bondList);
 
     // Finally, re-number the atoms if missing atoms were created.
     int currentN = activeMolecularAssembly.getAtomArray().length;
     boolean renumber = forceField.getBoolean("renumber-pdb", false);
     if (pdbAtoms != currentN) {
       logger.info(format(" Renumbering PDB file due to built atoms (%d vs %d)", currentN, pdbAtoms));
       numberAtoms(activeMolecularAssembly);
     } else if (renumber) {
       logger.info(" Renumbering PDB file due to renumber-pdb flag.");
       numberAtoms(activeMolecularAssembly);
     }
     return true;
   }
 
   /**
    * Removes inappropriate hydrogen atoms from residues in the active molecular assembly.
    * This method iterates through the residue list of the active molecular assembly and
    * identifies residues requiring hydrogen removal (e.g., specific residues such as "HID", "HIE", "ASP", etc.).
    * Residue names are defined by the C-alpha atom.
    */
   public void removeInappropriateHydrogen() {
     StringBuilder sb = new StringBuilder();
     int numRemoved = 0;
     for (Residue residue : activeMolecularAssembly.getResidueList()) {
       if (residue.getName().equals("ACE") ||
           residue.getName().equals("NME") ||
           residue.getResidueType() != Residue.ResidueType.AA) {
         continue;
       }
       String trueResName = residue.getAtomByName("CA", true).getResidueName();
       Atom atom;
       switch (trueResName) {
         case "HID", "GLU" -> // No HE2
             atom = residue.getAtomByName("HE2", true);
         case "HIE" -> // No HD1
             atom = residue.getAtomByName("HD1", true);
         case "ASP" -> // No HD2
             atom = residue.getAtomByName("HD2", true);
         case "LYD" -> // No HZ3
             atom = residue.getAtomByName("HZ3", true);
         case "CYD" -> // No HG
             atom = residue.getAtomByName("HG", true);
         default -> atom = null;
         // Do nothing.
       }
       if (atom != null) {
         MSNode atoms = residue.getAtomNode();
         atoms.remove(atom);
         residue.setName(trueResName);
         sb.append(" Removed ").append(atom);
         numRemoved++;
       }
     }
     if (numRemoved > 0) {
       logger.info(format(" Removed %d Inappropriate Hydrogen", numRemoved));
       logger.info(sb.toString());
     }
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public boolean readNext() {
     return readNext(false);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public boolean readNext(boolean resetPosition) {
     return readNext(resetPosition, false);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public boolean readNext(boolean resetPosition, boolean print) {
     return readNext(resetPosition, print, true);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   @SuppressWarnings("fallthrough")
   public boolean readNext(boolean resetPosition, boolean print, boolean parse) {
     modelsRead = resetPosition ? 1 : modelsRead + 1;
     if (!parse) {
       if (print) {
         logger.info(format(" Skipped Model %d.", modelsRead));
       }
       return true;
     }
     remarkLines = new ArrayList<>(remarkLines.size());
     // ^ is beginning of line, \\s+ means "one or more whitespace", (\\d+) means match and capture
     // one or more digits.
     Pattern modelPatt = Pattern.compile("^MODEL\\s+(\\d+)");
     boolean eof = true;
     for (MolecularAssembly system : systems) {
       try {
         BufferedReader currentReader;
         if (readers.containsKey(system)) {
           currentReader = readers.get(system);
           try {
             if (!currentReader.ready()) {
               currentReader = new BufferedReader(new FileReader(readFile));
               // Mark the start of the file.
               currentReader.mark(0);
               readers.remove(system);
               readers.put(system, currentReader);
             } else if (resetPosition) {
               // If the BufferedReader has been opened, and reset is requested, reset the position.
               currentReader.reset();
             }
           } catch (Exception exception) {
             // If all structures in the PDB file have been read, the currentReader may have closed.
             // The try block will catch this case and reset to the beginning of the file.
             currentReader = new BufferedReader(new FileReader(readFile));
             // Mark the start of the file.
             currentReader.mark(0);
             readers.remove(system);
             readers.put(system, currentReader);
           }
         } else {
           currentReader = new BufferedReader(new FileReader(readFile));
           // Mark the start of the file.
           currentReader.mark(0);
           readers.put(system, currentReader);
         }
 
         // Skip to appropriate model.
         String line = currentReader.readLine();
         while (line != null) {
           line = line.trim();
           Matcher m = modelPatt.matcher(line);
           if (m.find()) {
             int modelNum = parseInt(m.group(1));
             if (modelNum == modelsRead) {
               if (print) {
                 logger.log(Level.INFO, format(" Reading model %d for %s", modelNum, currentFile));
               }
               eof = false;
               break;
             }
           }
           line = currentReader.readLine();
         }
         if (eof) {
           if (logger.isLoggable(Level.FINEST)) {
             logger.log(Level.FINEST, format("\n End of file reached for %s", readFile));
           }
           currentReader.close();
           return false;
         }
 
         // Begin parsing the model.
         currentChainID = null;
         currentSegID = null;
         boolean modelDone = false;
         line = currentReader.readLine();
         while (line != null) {
           line = line.trim();
           String recID = line.substring(0, Math.min(6, line.length())).trim();
           try {
             Record record = Record.valueOf(recID);
             boolean hetatm = true;
             switch (record) {
               // =============================================================================
               //
               //  7 - 11        Integer       serial       Atom serial number.
               // 13 - 16        Atom          name         Atom name.
               // 17             Character     altLoc       Alternate location indicator.
               // 18 - 20        Residue name  resName      Residue name.
               // 22             Character     chainID      Chain identifier.
               // 23 - 26        Integer       resSeq       Residue sequence number.
               // 27             AChar         iCode        Code for insertion of residues.
               // 31 - 38        Real(8.3)     x            Orthogonal coordinates for X in
               // Angstroms.
               // 39 - 46        Real(8.3)     y            Orthogonal coordinates for Y in
               // Angstroms.
               // 47 - 54        Real(8.3)     z            Orthogonal coordinates for Z in
               // Angstroms.
               // 55 - 60        Real(6.2)     occupancy    Occupancy.
               // 61 - 66        Real(6.2)     tempFactor   Temperature factor.
               // 77 - 78        LString(2)    element      Element symbol, right-justified.
               // 79 - 80        LString(2)    charge       Charge  on the atom.
               // =============================================================================
               //         1         2         3         4         5         6         7
               // 123456789012345678901234567890123456789012345678901234567890123456789012345678
               // ATOM      1  N   ILE A  16      60.614  71.140 -10.592  1.00  7.38           N
               // ATOM      2  CA  ILE A  16      60.793  72.149  -9.511  1.00  6.91           C
               case ATOM:
                 hetatm = false;
               case HETATM:
                 String name = line.substring(12, 16).trim();
                 if (name.toUpperCase().contains("1H") || name.toUpperCase().contains("2H")
                     || name.toUpperCase().contains("3H")) {
                   // VERSION3_2 is presently just a placeholder for "anything non-standard".
                   fileStandard = VERSION3_2;
                 }
                 Character altLoc = line.substring(16, 17).toUpperCase().charAt(0);
                 if (!altLoc.equals(' ') && !altLoc.equals(currentAltLoc)) {
                   break;
                 }
                 // if (!altLoc.equals(' ') && !altLoc.equals('A') && !altLoc.equals(currentAltLoc)) {
                 //  break;
                 // }
                 String resName = line.substring(17, 20).trim();
                 Character chainID = line.substring(21, 22).charAt(0);
                 String segID = getExistingSegID(chainID);
                 int resSeq = Hybrid36.decode(4, line.substring(22, 26));
                 double[] d = new double[3];
                 d[0] = parseDouble(line.substring(30, 38).trim());
                 d[1] = parseDouble(line.substring(38, 46).trim());
                 d[2] = parseDouble(line.substring(46, 54).trim());
                 double occupancy = 1.0;
                 double tempFactor = 1.0;
                 Atom newAtom = new Atom(0, name, altLoc, d, resName, resSeq, chainID, occupancy,
                     tempFactor, segID);
                 newAtom.setHetero(hetatm);
                 // Check if this is a modified residue.
                 if (modRes.containsKey(resName.toUpperCase())) {
                   newAtom.setModRes(true);
                 }
 
                 Atom returnedAtom = activeMolecularAssembly.findAtom(newAtom);
                 if (returnedAtom != null) {
                   returnedAtom.setXYZ(d);
                   double[] retXYZ = new double[3];
                   returnedAtom.getXYZ(retXYZ);
                 } else {
                   String message = format(" Could not find atom %s in assembly", newAtom);
                   if (dieOnMissingAtom) {
                     logger.severe(message);
                   } else {
                     logger.warning(message);
                   }
                 }
                 break;
               case CRYST1:
                 // =============================================================================
                 // The CRYST1 record presents the unit cell parameters, space group, and Z
                 // value. If the structure was not determined by crystallographic means, CRYST1
                 // simply provides the unitary values, with an appropriate REMARK.
                 //
                 //  7 - 15       Real(9.3)     a              a (Angstroms).
                 // 16 - 24       Real(9.3)     b              b (Angstroms).
                 // 25 - 33       Real(9.3)     c              c (Angstroms).
                 // 34 - 40       Real(7.2)     alpha          alpha (degrees).
                 // 41 - 47       Real(7.2)     beta           beta (degrees).
                 // 48 - 54       Real(7.2)     gamma          gamma (degrees).
                 // 56 - 66       LString       sGroup         Space  group.
                 // 67 - 70       Integer       z              Z value.
                 // =============================================================================
                 logger.fine(" Crystal record found.");
                 if (line.length() < 55) {
                   logger.severe(" CRYST1 record is improperly formatted.");
                 }
                 double aaxis = parseDouble(line.substring(6, 15).trim());
                 double baxis = parseDouble(line.substring(15, 24).trim());
                 double caxis = parseDouble(line.substring(24, 33).trim());
                 double alpha = parseDouble(line.substring(33, 40).trim());
                 double beta = parseDouble(line.substring(40, 47).trim());
                 double gamma = parseDouble(line.substring(47, 54).trim());
                 int limit = min(line.length(), 66);
                 String sg = line.substring(55, limit).trim();
 //                properties.clearProperty("a-axis");
 //                properties.clearProperty("b-axis");
 //                properties.clearProperty("c-axis");
 //                properties.clearProperty("alpha");
 //                properties.clearProperty("beta");
 //                properties.clearProperty("gamma");
 //                properties.clearProperty("spacegroup");
 //
 //                properties.addProperty("a-axis", aaxis);
 //                properties.addProperty("b-axis", baxis);
 //                properties.addProperty("c-axis", caxis);
 //                properties.addProperty("alpha", alpha);
 //                properties.addProperty("beta", beta);
 //                properties.addProperty("gamma", gamma);
 //                properties.addProperty("spacegroup", SpaceGroupInfo.pdb2ShortName(sg));
                 Crystal crystal = activeMolecularAssembly.getCrystal();
                 SpaceGroup spaceGroup = SpaceGroupDefinitions.spaceGroupFactory(sg);
                 if (Objects.equals(crystal.spaceGroup.shortName, spaceGroup.shortName)) {
                   crystal.changeUnitCellParameters(aaxis, baxis, caxis, alpha, beta, gamma);
                 } else {
                   // TODO: Handle changes in space groups... Means recalculating force field terms.
                   logger.warning(format(" Original space group %s could not be changed to %s",
                       crystal.spaceGroup.shortName, spaceGroup.shortName));
                 }
                 break;
               case ENDMDL:
               case END: // Technically speaking, END should be at the end of the file, not end of
                 // the model.
                 logger.log(Level.FINE, format(" Model %d successfully read", modelsRead));
                 modelDone = true;
                 break;
               case REMARK:
                 remarkLines.add(line.trim());
                 if (line.contains("Lambda:")) {
                   Matcher m = lambdaPattern.matcher(line);
                   if (m.find()) {
                     lastReadLambda = Double.parseDouble(m.group(1));
                   }
                 }
                 break;
               default:
                 break;
             }
           } catch (Exception ex) {
             // Do nothing; it's not an ATOM/HETATM line.
           }
           if (modelDone) {
             break;
           }
           line = currentReader.readLine();
         }
         return true;
       } catch (IOException ex) {
         logger.info(
             format(" Exception in parsing frame %d of %s:" + " %s", modelsRead, system.toString(), ex));
       }
     }
     return false;
   }
 
   /**
    * Specify the alternate location.
    *
    * @param molecularAssembly The MolecularAssembly to populate.
    * @param altLoc            The alternate location to use.
    */
   public void setAltID(MolecularAssembly molecularAssembly, Character altLoc) {
     setMolecularSystem(molecularAssembly);
     currentAltLoc = altLoc;
   }
 
   /**
    * Sets whether this PDBFilter should log each time it saves to a file.
    *
    * @param logWrites a boolean.
    */
   public void setLogWrites(boolean logWrites) {
     this.logWrites = logWrites;
   }
 
   /**
    * setModelNumbering.
    *
    * @param modelsWritten the number of models written.
    */
   public void setModelNumbering(int modelsWritten) {
     this.modelsWritten = modelsWritten;
   }
 
   public void setLMN(int[] lmn) {
     if (lmn[0] >= 1 && lmn[1] >= 1 && lmn[2] >= 1) {
       this.lmn = lmn;
     } else {
       // Provided dimensions are not handled. Revert to P1.
       this.lmn = new int[]{1, 1, 1};
     }
   }
 
   /**
    * setSymOp.
    *
    * @param symOp a int.
    */
   public void setSymOp(int symOp) {
     this.nSymOp = symOp;
   }
 
   /**
    * Expand the current system to P1 during the save operation.
    *
    * @param file The file to write.
    * @return Return true on a successful write.
    */
   public boolean writeFileAsP1(File file) {
     // XYZ File First Line
     final int l = lmn[0];
     final int m = lmn[1];
     final int n = lmn[2];
     Crystal crystal = activeMolecularAssembly.getCrystal();
     int nSymOps = crystal.getUnitCell().spaceGroup.getNumberOfSymOps();
 
     if (nSymOps == 1 && l <= 1 && m <= 1 && n <= 1) {
       // This is a P1 system.
       if (!writeFile(file, false)) {
         logger.info(format(" Save failed for %s", activeMolecularAssembly));
         return false;
       } else {
         return true;
       }
     } else {
       Polymer[] polymers = activeMolecularAssembly.getChains();
       int chainCount = 0;
       for (Polymer polymer : polymers) {
         Character chainID = Polymer.CHAIN_IDS.charAt(chainCount++);
         polymer.setChainID(chainID);
         polymer.setSegID(chainID.toString());
       }
       nSymOp = 0;
       logWrites = false;
       boolean writeEnd = false;
       if (!writeFile(file, false, false, writeEnd)) {
         logger.info(format(" Save failed for %s", activeMolecularAssembly));
         return false;
       } else {
         for (int i = 0; i < l; i++) {
           for (int j = 0; j < m; j++) {
             for (int k = 0; k < n; k++) {
               lValue = i;
               mValue = j;
               nValue = k;
               for (int iSym = 0; iSym < nSymOps; iSym++) {
                 nSymOp = iSym;
                 for (Polymer polymer : polymers) {
                   Character chainID = Polymer.CHAIN_IDS.charAt(chainCount++);
                   polymer.setChainID(chainID);
                   polymer.setSegID(chainID.toString());
                 }
                 // If the last sym op to be written.
                 writeEnd = iSym == nSymOps - 1 && i == l - 1 && j == m - 1 && k == n - 1;
                 if (!writeFile(file, true, false, writeEnd)) {
                   logger.info(format(" Save failed for %s", activeMolecularAssembly));
                   return false;
                 }
               }
             }
           }
         }
       }
 
       // Reset the chainIDs.
       chainCount = 0;
       for (Polymer polymer : polymers) {
         Character chainID = Polymer.CHAIN_IDS.charAt(chainCount++);
         polymer.setChainID(chainID);
         polymer.setSegID(chainID.toString());
       }
 
     }
 
     return true;
   }
 
   /**
    * writeFile
    *
    * @param saveFile    a {@link java.io.File} object.
    * @param append      Whether to append to saveFile (vs over-write).
    * @param printLinear Ignored (remains to present a different method signature).
    * @param writeEnd    True if this is the final model.
    * @return Success of writing.
    */
   public boolean writeFile(File saveFile, boolean append, boolean printLinear, boolean writeEnd) {
     return writeFile(saveFile, append, Collections.emptySet(), writeEnd, true);
   }
 
   /**
    * writeFile
    *
    * @param saveFile   a {@link java.io.File} object to save to.
    * @param append     Whether to append to saveFile (vs over-write).
    * @param toExclude  A {@link java.util.Set} of {@link ffx.potential.bonded.Atom}s to exclude
    *                   from writing.
    * @param writeEnd   True if this is the final model.
    * @param versioning True if the file being saved to should be versioned. False if the file
    *                   being saved to should be overwritten.
    * @return Success of writing.
    */
   public boolean writeFile(File saveFile, boolean append, Set<Atom> toExclude, boolean writeEnd,
                            boolean versioning) {
     return writeFile(saveFile, append, toExclude, writeEnd, versioning, null);
   }
 
   /**
    * writeFile
    *
    * @param saveFile   a {@link java.io.File} object to save to.
    * @param append     Whether to append to saveFile (vs over-write).
    * @param toExclude  A {@link java.util.Set} of {@link ffx.potential.bonded.Atom}s to exclude
    *                   from writing.
    * @param writeEnd   True if this is the final model.
    * @param versioning True if the file being saved to should be versioned. False if the file
    *                   being saved to should be overwritten.
    * @param extraLines Extra comment/header lines to write.
    * @return Success of writing.
    */
   public boolean writeFile(File saveFile, boolean append, Set<Atom> toExclude, boolean writeEnd,
                            boolean versioning, String[] extraLines) {
     // Set standardize atom names to false in the presence of deuterium
     if (standardizeAtomNames) {
       logger.info(" Setting atom names to PDB standard.");
 
       List<Atom> deuteriumAtoms = new ArrayList<>();
       for (Atom atom : activeMolecularAssembly.getAtomArray()) {
         if (atom.getName().startsWith("D")) {
           String name = atom.getName().replaceFirst("D", "H");
           atom.setName(name);
           deuteriumAtoms.add(atom);
         }
       }
       renameAtomsToPDBStandard(activeMolecularAssembly);
       for (Atom atom : activeMolecularAssembly.getAtomArray()) {
         if (deuteriumAtoms.contains(atom) && atom.getName().startsWith("H")) {
           String name = atom.getName().replaceFirst("H", "D");
           atom.setName(name);
         }
       }
     }
 
     final Set<Atom> atomExclusions = toExclude == null ? Collections.emptySet() : toExclude;
     if (saveFile == null) {
       return false;
     }
     if (vdwH) {
       logger.info(" Saving hydrogen to van der Waals centers instead of nuclear locations.");
     }
     if (nSymOp > -1) {
       logger.info(format(" Saving atoms using the symmetry operator:\n%s\n",
           activeMolecularAssembly.getCrystal().getUnitCell().spaceGroup.getSymOp(nSymOp)
               .toString()));
     }
 
     // Create StringBuilders for ATOM, ANISOU and TER records that can be reused.
     StringBuilder sb = new StringBuilder("ATOM  ");
     StringBuilder anisouSB = new StringBuilder("ANISOU");
     StringBuilder terSB = new StringBuilder("TER   ");
     StringBuilder model = null;
     for (int i = 6; i < 80; i++) {
       sb.append(' ');
       anisouSB.append(' ');
       terSB.append(' ');
     }
 
     File newFile = saveFile;
     if (!append) {
       if (versioning) {
         newFile = version(saveFile);
       }
     } else if (modelsWritten >= 0) {
       model = new StringBuilder(format("MODEL     %-4d", ++modelsWritten));
       model.append(repeat(" ", 65));
     }
     activeMolecularAssembly.setFile(newFile);
     if (activeMolecularAssembly.getName() == null) {
       activeMolecularAssembly.setName(newFile.getName());
     }
     if (logWrites) {
       logger.log(Level.INFO, " Saving {0}", newFile.getName());
     }
 
     try (FileWriter fw = new FileWriter(newFile, append);
          BufferedWriter bw = new BufferedWriter(fw)) {
       /*
        Will come before CRYST1 and ATOM records, but after anything
        written by writeFileWithHeader (particularly X-ray refinement statistics).
       */
       String[] headerLines = activeMolecularAssembly.getHeaderLines();
       for (String line : headerLines) {
         bw.write(format("%s\n", line));
       }
       if (extraLines != null) {
         if (rotamerTitration && extraLines[0].contains("REMARK")) {
           for (String line : extraLines) {
             bw.write(line + "\n");
           }
         } else {
           for (String line : extraLines) {
             bw.write(format("REMARK 999 %s\n", line));
           }
         }
       }
       if (model != null) {
         bw.write(model.toString());
         bw.newLine();
       }
       // =============================================================================
       // The CRYST1 record presents the unit cell parameters, space group, and Z
       // value. If the structure was not determined by crystallographic means, CRYST1
       // simply provides the unitary values, with an appropriate REMARK.
       //
       //  7 - 15       Real(9.3)     a              a (Angstroms).
       // 16 - 24       Real(9.3)     b              b (Angstroms).
       // 25 - 33       Real(9.3)     c              c (Angstroms).
       // 34 - 40       Real(7.2)     alpha          alpha (degrees).
       // 41 - 47       Real(7.2)     beta           beta (degrees).
       // 48 - 54       Real(7.2)     gamma          gamma (degrees).
       // 56 - 66       LString       sGroup         Space  group.
       // 67 - 70       Integer       z              Z value.
       // =============================================================================
       if (nSymOp < 0) {
         // Write out the unit cell.
         Crystal crystal = activeMolecularAssembly.getCrystal();
         if (crystal != null && !crystal.aperiodic()) {
           Crystal c = crystal.getUnitCell();
           if (lmn[0] > 0 || lmn[1] > 0 || lmn[2] > 0) {
             c.a = c.a * lmn[0];
             c.b = c.b * lmn[1];
             c.c = c.c * lmn[2];
           }
           bw.write(c.toCRYST1());
         }
       } else if (nSymOp == 0) {
         // Write a P1 cell.
         Crystal crystal = activeMolecularAssembly.getCrystal();
         if (crystal != null && !crystal.aperiodic()) {
           Crystal c = crystal.getUnitCell();
           Crystal p1 = new Crystal((lmn[0] > 0) ? c.a * lmn[0] : c.a, (lmn[1] > 0) ? c.b * lmn[1] : c.b, (lmn[2] > 0) ? c.c * lmn[2] : c.c, c.alpha, c.beta, c.gamma, "P1");
           bw.write(p1.toCRYST1());
         }
       }
       // =============================================================================
       // The SSBOND record identifies each disulfide bond in protein and polypeptide
       // structures by identifying the two residues involved in the bond.
       // The disulfide bond distance is included after the symmetry operations at
       // the end of the SSBOND record.
       //
       //  8 - 10        Integer         serNum       Serial number.
       // 12 - 14        LString(3)      "CYS"        Residue name.
       // 16             Character       chainID1     Chain identifier.
       // 18 - 21        Integer         seqNum1      Residue sequence number.
       // 22             AChar           icode1       Insertion code.
       // 26 - 28        LString(3)      "CYS"        Residue name.
       // 30             Character       chainID2     Chain identifier.
       // 32 - 35        Integer         seqNum2      Residue sequence number.
       // 36             AChar           icode2       Insertion code.
       // 60 - 65        SymOP           sym1         Symmetry oper for 1st resid
       // 67 - 72        SymOP           sym2         Symmetry oper for 2nd resid
       // 74 – 78        Real(5.2)      Length        Disulfide bond distance
       //
       // If SG of cysteine is disordered then there are possible alternate linkages.
       // wwPDB practice is to put together all possible SSBOND records. This is
       // problematic because the alternate location identifier is not specified in
       // the SSBOND record.
       // =============================================================================
       int serNum = 1;
       Polymer[] polymers = activeMolecularAssembly.getChains();
       if (polymers != null) {
         for (Polymer polymer : polymers) {
           List<Residue> residues = polymer.getResidues();
           for (Residue residue : residues) {
             if (residue.getName().equalsIgnoreCase("CYS")) {
               List<Atom> cysAtoms = residue.getAtomList().stream()
                   .filter(a -> !atomExclusions.contains(a)).toList();
               Atom SG1 = null;
               for (Atom atom : cysAtoms) {
                 String atName = atom.getName().toUpperCase();
                 if (atName.equals("SG") || atName.equals("SH")
                     || atom.getAtomType().atomicNumber == 16) {
                   SG1 = atom;
                   break;
                 }
               }
               List<Bond> bonds = SG1.getBonds();
               for (Bond bond : bonds) {
                 Atom SG2 = bond.get1_2(SG1);
                 if (SG2.getAtomType().atomicNumber == 16 && !atomExclusions.contains(SG2)) {
                   if (SG1.getIndex() < SG2.getIndex()) {
                     bond.energy(false);
                     bw.write(format("SSBOND %3d CYS %1s %4s    CYS %1s %4s %36s %5.2f\n", serNum++,
                         SG1.getChainID().toString(), Hybrid36.encode(4, SG1.getResidueNumber()),
                         SG2.getChainID().toString(), Hybrid36.encode(4, SG2.getResidueNumber()), "",
                         bond.getValue()));
                   }
                 }
               }
             }
           }
         }
       }
       // =============================================================================
       //
       //  7 - 11        Integer       serial       Atom serial number.
       // 13 - 16        Atom          name         Atom name.
       // 17             Character     altLoc       Alternate location indicator.
       // 18 - 20        Residue name  resName      Residue name.
       // 22             Character     chainID      Chain identifier.
       // 23 - 26        Integer       resSeq       Residue sequence number.
       // 27             AChar         iCode        Code for insertion of residues.
       // 31 - 38        Real(8.3)     x            Orthogonal coordinates for X in Angstroms.
       // 39 - 46        Real(8.3)     y            Orthogonal coordinates for Y in Angstroms.
       // 47 - 54        Real(8.3)     z            Orthogonal coordinates for Z in Angstroms.
       // 55 - 60        Real(6.2)     occupancy    Occupancy.
       // 61 - 66        Real(6.2)     tempFactor   Temperature factor.
       // 77 - 78        LString(2)    element      Element symbol, right-justified.
       // 79 - 80        LString(2)    charge       Charge  on the atom.
       // =============================================================================
       //         1         2         3         4         5         6         7
       // 123456789012345678901234567890123456789012345678901234567890123456789012345678
       // ATOM      1  N   ILE A  16      60.614  71.140 -10.592  1.00  7.38           N
       // ATOM      2  CA  ILE A  16      60.793  72.149  -9.511  1.00  6.91           C
       MolecularAssembly[] molecularAssemblies = this.getMolecularAssemblyArray();
       int serial = 1;
       if (nSymOp > 0) {
         serial = serialP1;
       }
 
       // Loop over biomolecular chains
       if (polymers != null) {
         for (Polymer polymer : polymers) {
           currentSegID = polymer.getName();
           currentChainID = polymer.getChainID();
           sb.setCharAt(21, currentChainID);
           // Loop over residues
           List<Residue> residues = polymer.getResidues();
           for (Residue residue : residues) {
             String resName = residue.getName();
             if (resName.length() > 3) {
               resName = resName.substring(0, 3);
             }
             int resID = residue.getResidueNumber();
             sb.replace(17, 20, padLeft(resName.toUpperCase(), 3));
             sb.replace(22, 26, format("%4s", Hybrid36.encode(4, resID)));
             // Loop over atoms
             List<Atom> residueAtoms = residue.getAtomList().stream()
                 .filter(a -> !atomExclusions.contains(a)).collect(Collectors.toList());
             boolean altLocFound = false;
             for (Atom atom : residueAtoms) {
               if (mutate) {
                 for (Mutation mtn : mutations) {
                   if (resID == mtn.resID && currentChainID == mtn.chainChar) {
                     mtn.addTors(atom, serial);
                     ArrayList<String> alchAtoms = mtn.getAlchemicalAtoms(true);
                     if (alchAtoms != null) {
                       if (residue.getBackboneAtoms().contains(atom) && alchAtoms.contains(atom.getName())) {
                         logger.info(format(" MUTATION atom is %d chain %s", serial, currentChainID));
                       }
                     } else {
                       // treating pur-pyr or pyr-pur N9/N1 & C2/C4 as alchemical
                       if (residue.getBackboneAtoms().contains(atom)) {
                         logger.info(format(" MUTATION atom is %d chain %s", serial, currentChainID));
                       }
                     }
                   }
                 }
               }
               writeAtom(atom, serial++, sb, anisouSB, bw);
               Character altLoc = atom.getAltLoc();
               if (altLoc != null && !altLoc.equals(' ')) {
                 altLocFound = true;
               }
             }
             // Write out alternate conformers
             if (altLocFound) {
               for (int ma = 1; ma < molecularAssemblies.length; ma++) {
                 MolecularAssembly altMolecularAssembly = molecularAssemblies[ma];
                 Polymer altPolymer = altMolecularAssembly.getPolymer(currentChainID, currentSegID, false);
                 Residue altResidue = altPolymer.getResidue(resName, resID, false, Residue.ResidueType.AA);
                 if (altResidue == null) {
                   resName = AminoAcid3.UNK.name();
                   altResidue = altPolymer.getResidue(resName, resID, false, Residue.ResidueType.AA);
                 }
                 residueAtoms = altResidue.getAtomList().stream()
                     .filter(a -> !atomExclusions.contains(a)).toList();
                 for (Atom atom : residueAtoms) {
                   if (atom.getAltLoc() != null && !atom.getAltLoc().equals(' ') && !atom.getAltLoc()
                       .equals('A')) {
                     sb.replace(17, 20, padLeft(atom.getResidueName().toUpperCase(), 3));
                     writeAtom(atom, serial++, sb, anisouSB, bw);
                   }
                 }
               }
             }
           }
           terSB.replace(6, 11, format("%5s", Hybrid36.encode(5, serial++)));
           terSB.replace(12, 16, "    ");
           terSB.replace(16, 26, sb.substring(16, 26));
           bw.write(terSB.toString());
           bw.newLine();
         }
       }
       sb.replace(0, 6, "HETATM");
       sb.setCharAt(21, 'A');
 
       Character chainID = 'A';
       if (polymers != null) {
         chainID = polymers[0].getChainID();
       }
       activeMolecularAssembly.setChainIDAndRenumberMolecules(chainID);
 
       // Loop over molecules, ions and then water.
       List<MSNode> molecules = activeMolecularAssembly.getMolecules();
       int numMolecules = molecules.size();
       for (int i = 0; i < numMolecules; i++) {
         Molecule molecule = (Molecule) molecules.get(i);
         chainID = molecule.getChainID();
         sb.setCharAt(21, chainID);
         String resName = molecule.getResidueName();
         int resID = molecule.getResidueNumber();
         if (resName.length() > 3) {
           resName = resName.substring(0, 3);
         }
         sb.replace(17, 20, padLeft(resName.toUpperCase(), 3));
         sb.replace(22, 26, format("%4s", Hybrid36.encode(4, resID)));
         // List<Atom> moleculeAtoms = molecule.getAtomList();
         List<Atom> moleculeAtoms = molecule.getAtomList().stream()
             .filter(a -> !atomExclusions.contains(a)).collect(Collectors.toList());
         boolean altLocFound = false;
         for (Atom atom : moleculeAtoms) {
           writeAtom(atom, serial++, sb, anisouSB, bw);
           Character altLoc = atom.getAltLoc();
           if (altLoc != null && !altLoc.equals(' ')) {
             altLocFound = true;
           }
         }
         // Write out alternate conformers
         if (altLocFound) {
           for (int ma = 1; ma < molecularAssemblies.length; ma++) {
             MolecularAssembly altMolecularAssembly = molecularAssemblies[ma];
             MSNode altmolecule = altMolecularAssembly.getMolecules().get(i);
             moleculeAtoms = altmolecule.getAtomList();
             for (Atom atom : moleculeAtoms) {
               if (atom.getAltLoc() != null && !atom.getAltLoc().equals(' ') && !atom.getAltLoc()
                   .equals('A')) {
                 writeAtom(atom, serial++, sb, anisouSB, bw);
               }
             }
           }
         }
       }
 
       List<MSNode> ions = activeMolecularAssembly.getIons();
       for (int i = 0; i < ions.size(); i++) {
         Molecule ion = (Molecule) ions.get(i);
         chainID = ion.getChainID();
         sb.setCharAt(21, chainID);
         String resName = ion.getResidueName();
         int resID = ion.getResidueNumber();
         if (resName.length() > 3) {
           resName = resName.substring(0, 3);
         }
         sb.replace(17, 20, padLeft(resName.toUpperCase(), 3));
         sb.replace(22, 26, format("%4s", Hybrid36.encode(4, resID)));
         // List<Atom> ionAtoms = ion.getAtomList();
         List<Atom> ionAtoms = ion.getAtomList().stream().filter(a -> !atomExclusions.contains(a))
             .collect(Collectors.toList());
         boolean altLocFound = false;
         for (Atom atom : ionAtoms) {
           writeAtom(atom, serial++, sb, anisouSB, bw);
           Character altLoc = atom.getAltLoc();
           if (altLoc != null && !altLoc.equals(' ')) {
             altLocFound = true;
           }
         }
         // Write out alternate conformers
         if (altLocFound) {
           for (int ma = 1; ma < molecularAssemblies.length; ma++) {
             MolecularAssembly altMolecularAssembly = molecularAssemblies[ma];
             MSNode altion = altMolecularAssembly.getIons().get(i);
             ionAtoms = altion.getAtomList();
             for (Atom atom : ionAtoms) {
               if (atom.getAltLoc() != null && !atom.getAltLoc().equals(' ') && !atom.getAltLoc()
                   .equals('A')) {
                 writeAtom(atom, serial++, sb, anisouSB, bw);
               }
             }
           }
         }
       }
 
       List<MSNode> water = activeMolecularAssembly.getWater();
       for (int i = 0; i < water.size(); i++) {
         Molecule wat = (Molecule) water.get(i);
         chainID = wat.getChainID();
         sb.setCharAt(21, chainID);
         String resName = wat.getResidueName();
         int resID = wat.getResidueNumber();
         if (resName.length() > 3) {
           resName = resName.substring(0, 3);
         }
         sb.replace(17, 20, padLeft(resName.toUpperCase(), 3));
         sb.replace(22, 26, format("%4s", Hybrid36.encode(4, resID)));
         List<Atom> waterAtoms = wat.getAtomList().stream().filter(a -> !atomExclusions.contains(a))
             .collect(Collectors.toList());
         boolean altLocFound = false;
         for (Atom atom : waterAtoms) {
           writeAtom(atom, serial++, sb, anisouSB, bw);
           Character altLoc = atom.getAltLoc();
           if (altLoc != null && !altLoc.equals(' ')) {
             altLocFound = true;
           }
         }
         // Write out alternate conformers
         if (altLocFound) {
           for (int ma = 1; ma < molecularAssemblies.length; ma++) {
             MolecularAssembly altMolecularAssembly = molecularAssemblies[ma];
             MSNode altwater = altMolecularAssembly.getWater().get(i);
             waterAtoms = altwater.getAtomList();
             for (Atom atom : waterAtoms) {
               if (atom.getAltLoc() != null && !atom.getAltLoc().equals(' ') && !atom.getAltLoc()
                   .equals('A')) {
                 writeAtom(atom, serial++, sb, anisouSB, bw);
               }
             }
           }
         }
       }
 
       if (model != null) {
         bw.write("ENDMDL");
         bw.newLine();
       }
 
       if (writeEnd) {
         bw.write("END");
         bw.newLine();
       }
 
       if (nSymOp >= 0) {
         serialP1 = serial;
       }
 
     } catch (Exception e) {
       String message = "Exception writing to file: " + saveFile;
       logger.log(Level.WARNING, message, e);
       return false;
     }
     return true;
   }
 
   /**
    * {@inheritDoc}
    *
    * <p>Write out the Atomic information in PDB format.
    */
   @Override
   public boolean writeFile(File saveFile, boolean append) {
     return writeFile(saveFile, append, false, true);
   }
 
   public boolean writeFile(File saveFile, boolean append, String[] extraLines) {
     return writeFile(saveFile, append, Collections.emptySet(), false, !append, extraLines);
   }
 
   /**
    * Writes out the atomic information in PDB format.
    *
    * @param saveFile   The file to save information to.
    * @param append     True if the current data should be appended to the saveFile (as in arc
    *                   files).
    * @param versioning True if the saveFile should be versioned. False if the saveFile should be
    *                   overwritten.
    * @return Success of writing.
    */
   public boolean writeFile(File saveFile, boolean append, boolean versioning) {
     return writeFile(saveFile, append, Collections.emptySet(), true, versioning);
   }
 
   /**
    * writeFileWithHeader.
    *
    * @param saveFile a {@link java.io.File} object.
    * @param header   a {@link java.lang.String} object.
    * @param append   a boolean.
    * @return a boolean.
    */
   public boolean writeFileWithHeader(File saveFile, String header, boolean append) {
     // Set standardize atom names to false in the presence of deuterium
     if (standardizeAtomNames) {
       List<Atom> deuteriumAtoms = new ArrayList<>();
       for (Atom atom : activeMolecularAssembly.getAtomArray()) {
         if (atom.getName().startsWith("D")) {
           String name = atom.getName().replaceFirst("D", "H");
           atom.setName(name);
           deuteriumAtoms.add(atom);
         }
       }
 
       logger.info(" Setting atom names to PDB standard.");
       renameAtomsToPDBStandard(activeMolecularAssembly);
 
       for (Atom atom : activeMolecularAssembly.getAtomArray()) {
         if (deuteriumAtoms.contains(atom) && atom.getName().startsWith("H")) {
           String name = atom.getName().replaceFirst("H", "D");
           atom.setName(name);
         }
       }
     }
     activeMolecularAssembly.setFile(saveFile);
     activeMolecularAssembly.setName(saveFile.getName());
 
     try (FileWriter fw = new FileWriter(saveFile, append); BufferedWriter bw = new BufferedWriter(
         fw)) {
       bw.write(header);
       bw.newLine();
     } catch (Exception e) {
       String message = " Exception writing to file: " + saveFile;
       logger.log(Level.WARNING, message, e);
       return false;
     }
     if (writeFile(saveFile, true)) {
       logger.log(Level.INFO, " Wrote PDB to file {0}", saveFile.getPath());
       return true;
     } else {
       logger.log(Level.INFO, " Error writing to file {0}", saveFile.getPath());
       return false;
     }
   }
 
   /**
    * writeFileWithHeader.
    *
    * @param saveFile a {@link java.io.File} object.
    * @param header   a {@link java.lang.String} object.
    * @return a boolean.
    */
   public boolean writeFileWithHeader(File saveFile, String header) {
     return writeFileWithHeader(saveFile, header, true);
   }
 
   /**
    * writeFileWithHeader.
    *
    * @param saveFile a {@link java.io.File} object.
    * @param header   a {@link java.lang.StringBuilder} object.
    * @return a boolean.
    */
   public boolean writeFileWithHeader(File saveFile, StringBuilder header) {
     return writeFileWithHeader(saveFile, header.toString());
   }
 
   /**
    * Get unique SegID for possibly duplicate chain IDs.
    *
    * @param c chain ID just read.
    * @return a unique segID.
    */
   private String getExistingSegID(Character c) {
     if (c.equals(' ')) {
       c = 'A';
     }
 
     // If the chain ID has not changed, return the existing segID.
     if (c.equals(currentChainID)) {
       return currentSegID;
     } else {
       currentChainID = null;
     }
 
     List<String> segIDs = segidMap.get(c);
     if (segIDs != null) {
       if (segIDs.size() > 1) {
         if (currentSegID == null) {
           currentChainID = c;
           currentSegID = segIDs.getFirst();
           return segIDs.getFirst();
         } else if (currentSegID.length() == 1) {
           currentChainID = c;
           currentSegID = segIDs.get(1);
           return segIDs.get(1);
         } else if (currentSegID.length() == 2) {
           String s = currentSegID.substring(0, 1);
           int num = -2;
           try {
             num = Integer.parseInt(s);
           } catch (NumberFormatException e) {
             logger.severe(" SegID of length 2 does not start with an integer.");
           }
           currentChainID = c;
           currentSegID = segIDs.get(num + 1);
           return segIDs.get(num + 1);
         } else {
           logger.info(" Too many repeated chains. Using single letter for segID.");
         }
       }
       return segIDs.get(0);
     } else {
       logger.log(Level.INFO, format(" Creating SegID for to chain %s", c));
       return getSegID(c);
     }
   }
 
   /**
    * Convert possibly duplicate chain IDs into unique segIDs.
    *
    * @param c chain ID just read.
    * @return a unique segID.
    */
   private String getSegID(Character c) {
     if (c.equals(' ')) {
       c = 'A';
     }
 
     // If the chain ID has not changed, return the existing segID.
     if (c.equals(currentChainID)) {
       return currentSegID;
     }
 
     // Loop through existing segIDs to find the first one that is unused.
     int count = 0;
     for (String segID : segIDs) {
       if (segID.endsWith(c.toString())) {
         count++;
       }
     }
 
     // If the count is greater than 0, then append it.
     String newSegID;
     if (count == 0) {
       newSegID = c.toString();
     } else {
       newSegID = count + c.toString();
     }
     segIDs.add(newSegID);
     currentChainID = c;
     currentSegID = newSegID;
 
     if (segidMap.containsKey(c)) {
       segidMap.get(c).add(newSegID);
     } else {
       List<String> newChainList = new ArrayList<>();
       newChainList.add(newSegID);
       segidMap.put(c, newChainList);
     }
 
     return newSegID;
   }
 
   /**
    * writeAtom
    *
    * @param atom     a {@link ffx.potential.bonded.Atom} object.
    * @param serial   a int.
    * @param sb       a {@link java.lang.StringBuilder} object.
    * @param anisouSB a {@link java.lang.StringBuilder} object.
    * @param bw       a {@link java.io.BufferedWriter} object.
    * @throws java.io.IOException if any.
    */
   private void writeAtom(Atom atom, int serial, StringBuilder sb, StringBuilder anisouSB,
                          BufferedWriter bw) throws IOException {
     String name = atom.getName();
     int nameLength = name.length();
     if (nameLength > 4) {
       name = name.substring(0, 4);
     } else if (nameLength == 1) {
       name = name + "  ";
     } else if (nameLength == 2) {
       if (atom.getAtomType().valence == 0) {
         name = name + "  ";
       } else {
         name = name + " ";
       }
     }
     double[] xyz = vdwH ? atom.getRedXYZ() : atom.getXYZ(null);
     if (nSymOp >= 0) {
       Crystal crystal = activeMolecularAssembly.getCrystal().getUnitCell();
       SymOp symOp = crystal.spaceGroup.getSymOp(nSymOp);
       double[] newXYZ = new double[xyz.length];
       crystal.applySymOp(xyz, newXYZ, symOp);
       if (lValue > 0 || mValue > 0 || nValue > 0) {
         double[] translation = new double[]{lValue, mValue, nValue};
         crystal.getUnitCell().toCartesianCoordinates(translation, translation);
         newXYZ[0] += translation[0];
         newXYZ[1] += translation[1];
         newXYZ[2] += translation[2];
       }
       xyz = newXYZ;
     }
     sb.replace(6, 16, format("%5s " + padLeft(name.toUpperCase(), 4), Hybrid36.encode(5, serial)));
     Character altLoc = atom.getAltLoc();
     sb.setCharAt(16, Objects.requireNonNullElse(altLoc, ' '));
 
 
     /*
      * On the following code:
      * #1: StringBuilder.replace will allow for longer strings, expanding the StringBuilder's length if necessary.
      *
      * #2: sb was never re-initialized, so if there was overflow,
      * sb would continue to be > 80 characters long, resulting in broken PDB files
      *
      * #3: It may be wiser to have XYZ coordinates result in shutdown, not
      * truncation of coordinates. #4: Excessive B-factors aren't much of an
      * issue; if the B-factor is past 999.99, that's the difference between
      * "density extends to Venus" and "density extends to Pluto".
      */
     StringBuilder decimals = new StringBuilder();
     for (int i = 0; i < 3; i++) {
       try {
         decimals.append(StringUtils.fwFpDec(xyz[i], 8, 3));
       } catch (IllegalArgumentException ex) {
         String newValue = StringUtils.fwFpTrunc(xyz[i], 8, 3);
         logger.info(format(" XYZ %d coordinate %8.3f for atom %s "
             + "overflowed bounds of 8.3f string specified by PDB "
             + "format; truncating value to %s", i, xyz[i], atom, newValue));
         decimals.append(newValue);
       }
     }
     try {
       decimals.append(StringUtils.fwFpDec(atom.getOccupancy(), 6, 2));
     } catch (IllegalArgumentException ex) {
       logger.severe(
           format(" Occupancy %f for atom %s is impossible; " + "value must be between 0 and 1",
               atom.getOccupancy(), atom));
     }
     try {
       decimals.append(StringUtils.fwFpDec(atom.getTempFactor(), 6, 2));
     } catch (IllegalArgumentException ex) {
       String newValue = StringUtils.fwFpTrunc(atom.getTempFactor(), 6, 2);
       logger.info(format(" Atom temp factor %6.2f for atom %s overflowed "
               + "bounds of 6.2f string specified by PDB format; truncating " + "value to %s",
           atom.getTempFactor(), atom, newValue));
       decimals.append(newValue);
     }
     sb.replace(30, 66, decimals.toString());
 
     name = Atom.ElementSymbol.values()[atom.getAtomicNumber() - 1].toString();
     name = name.toUpperCase();
     if (atom.isDeuterium()) {
       name = "D";
     }
     sb.replace(76, 78, padLeft(name, 2));
     sb.replace(78, 80, format("%2d", 0));
     bw.write(sb.toString());
     bw.newLine();
     // =============================================================================
     //  1 - 6        Record name   "ANISOU"
     //  7 - 11       Integer       serial         Atom serial number.
     // 13 - 16       Atom          name           Atom name.
     // 17            Character     altLoc         Alternate location indicator
     // 18 - 20       Residue name  resName        Residue name.
     // 22            Character     chainID        Chain identifier.
     // 23 - 26       Integer       resSeq         Residue sequence number.
     // 27            AChar         iCode          Insertion code.
     // 29 - 35       Integer       u[0][0]        U(1,1)
     // 36 - 42       Integer       u[1][1]        U(2,2)
     // 43 - 49       Integer       u[2][2]        U(3,3)
     // 50 - 56       Integer       u[0][1]        U(1,2)
     // 57 - 63       Integer       u[0][2]        U(1,3)
     // 64 - 70       Integer       u[1][2]        U(2,3)
     // 77 - 78       LString(2)    element        Element symbol, right-justified.
     // 79 - 80       LString(2)    charge         Charge on the atom.
     // =============================================================================
     double[] anisou = atom.getAnisou(null);
     if (anisou != null) {
       anisouSB.replace(6, 80, sb.substring(6, 80));
       anisouSB.replace(28, 70,
           format("%7d%7d%7d%7d%7d%7d", (int) (anisou[0] * 1e4), (int) (anisou[1] * 1e4),
               (int) (anisou[2] * 1e4), (int) (anisou[3] * 1e4), (int) (anisou[4] * 1e4),
               (int) (anisou[5] * 1e4)));
       bw.write(anisouSB.toString());
       bw.newLine();
     }
   }
 
   /**
    * PDB records that are recognized.
    */
   private enum Record {
     ANISOU, ATOM, CONECT, CRYST1, DBREF, END, MODEL, ENDMDL, HELIX, HETATM, LINK, MTRIX1, MTRIX2, MTRIX3, MODRES, SEQRES, SHEET, SSBOND, REMARK
   }
 
   /**
    * Presently, VERSION3_3 is default, and VERSION3_2 is anything non-standard.
    */
   public enum PDBFileStandard {
     VERSION2_3, VERSION3_0, VERSION3_1, VERSION3_2, VERSION3_3
   }
 
   public static class Mutation {
 
     /**
      * Residue ID of the residue to mutate.
      */
     final int resID;
     /**
      * Residue name after mutation.
      */
     final String resName;
     /**
      * Character for the chain ID of the residue that will be mutated.
      */
     final char chainChar;
     /**
      * Residue name before mutation.
      */
     String origResName;
     /**
      * The 4 x,y,z glycosyl torsion atom coordinates.
      */
     double[][] glyco = new double[4][3];
     /**
      * The 4 atom indices of glycosyl torsion atoms.
      */
     int[] glycoAtomIndex = new int[4];
     /**
      * Index correction.
      */
     int indCorr;
 
     public Mutation(int resID, char chainChar, String newResName) {
       newResName = newResName.toUpperCase();
       if (newResName.length() != 3) {
         logger.log(Level.WARNING, format("Invalid mutation target: %s.", newResName));
       }
       int isAA = AminoAcidUtils.getAminoAcidNumber(newResName);
       int isNA = NucleicAcidUtils.getNucleicAcidNumber(newResName);
       if (isAA == -1 && isNA == -1) {
         logger.log(Level.WARNING, format("Invalid mutation target: %s.", newResName));
       }
       this.resID = resID;
       this.chainChar = chainChar;
       this.resName = newResName;
 
       String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
       indCorr = alphabet.indexOf(chainChar);
     }
 
     /**
      * Check to see if an atom is involved in the mutated base's glycosyl torsion. If the mutation is a switch from
      * purine to pyrimidine or vice versa, it will return '~name', meaning the name should be replaced but to include it
      * as an alchemical atom.
      *
      * @param atomName atom name to check
      * @return new name to use if it is involved in glycosyl torsion, null otherwise
      */
     public String isNonAlchemicalAtom(String atomName) {
       if (isWtPurine()) {
         if (atomName.equals("N9")) {
           if (isMtnPyrimidine()) {
             return "~N1";
           }
           return atomName;
         } else if (atomName.equals("C4")) {
           if (isMtnPyrimidine()) {
             return "~C2";
           }
           return atomName;
         }
         return null;
       }
 
       if (isWtPyrimidine()) {
         if (atomName.equals("N1")) {
           if (isMtnPurine()) {
             // here
             return "~N9";
           }
           return atomName;
         } else if (atomName.equals("C2")) {
           if (isMtnPurine()) {
             // here
             return "~C4";
           }
           return atomName;
         }
         return null;
       }
 
       return null;
     }
 
     /**
      * Determines what atoms should be alchemical for a purine to purine or pyrimidine to pyrimidine mutation.
      *
      * @param isWriting true if writing the pdb, false if reading the pdb
      * @return ArrayList of alchemical atoms, null if not a pur-pur or pyr-pyr mutation
      */
     public ArrayList<String> getAlchemicalAtoms(boolean isWriting) {
       // Log warning that the mutation input is the same residue and return nothing so prev. functionality is not changed
       if (resName.equals(origResName)) {
         logger.severe("Desired Mutation residue is the same as the original.");
         return null;
       }
 
       boolean purpur;
       if (isMtnPurine() && isWtPurine()) {
         purpur = true;
       } else if (isMtnPyrimidine() && isWtPyrimidine()) {
         purpur = false;
       } else {
         // Return nothing so previous functionality is not changed
         return null;
       }
 
       String res;
 
       // look at the mutation residue if writing or the original (wild type) residue if reading
       if (isWriting) {
         res = resName;
       } else {
         res = origResName;
       }
 
       ArrayList<String> list = new ArrayList<>();
       if (purpur) { // purine: either A to G or G to A
         if (res.equals("DAD") || res.equals("DA")) { // MTN is A
           list.add("N6");
           list.add("H61");
           list.add("H62");
           list.add("H2");
         } else { // MTN is G
           list.add("H1");
           list.add("N2");
           list.add("H21");
           list.add("H22");
           list.add("O6");
         }
       } else { // pyrimidine: either T to C or C to T
         if (res.equals("DTY") || res.equals("DT")) { // MTN is T
           list.add("H3");
           list.add("O4");
           list.add("C7");
           list.add("H71");
           list.add("H72");
           list.add("H73");
         } else { // MTN is C
           list.add("N4");
           list.add("H41");
           list.add("H42");
           list.add("H5");
         }
       }
       return list;
     }
 
     /**
      * Determine if the mutation residue is purine.
      *
      * @return true if mutation is purine
      */
     public boolean isMtnPurine() {
       return resName.equals("DA") || resName.equals("DG") || resName.equals("DAD") || resName.equals("DGU");
     }
 
     /**
      * Determine if the mutation residue is pyrimidine.
      *
      * @return true if mutation is pyrimidine
      */
     public boolean isMtnPyrimidine() {
       return resName.equals("DC") || resName.equals("DT") || resName.equals("DCY") || resName.equals("DTY");
     }
 
     /**
      * Determine if original (wild type) residue is purine.
      *
      * @return true if original residue is purine
      */
     public boolean isWtPurine() {
       return origResName.equals("DA") || origResName.equals("DG") || origResName.equals("DAD") || origResName.equals("DGU");
     }
 
     /**
      * Determine if original (wild type) residue is pyrimidine.
      *
      * @return true if original residue is pyrimidine
      */
     public boolean isWtPyrimidine() {
       return origResName.equals("DT") || origResName.equals("DC") || origResName.equals("DTY") || origResName.equals("DCY");
     }
 
     public void addTors(Atom atom, int index) {
       String name = atom.getName();
       if (name.equals("O4'")) {
         atom.getXYZ(glyco[0]);
         glycoAtomIndex[0] = index - indCorr;
       } else if (name.equals("C1'")) {
         atom.getXYZ(glyco[1]);
         glycoAtomIndex[1] = index - indCorr;
       } else if (name.equals("N9") || (name.equals("N1") && isMtnPyrimidine())) {
         atom.getXYZ(glyco[2]);
         glycoAtomIndex[2] = index - indCorr;
       } else if ((name.equals("C4") && isMtnPurine()) || (name.equals("C2") && isMtnPyrimidine())) {
         atom.getXYZ(glyco[3]);
         glycoAtomIndex[3] = index - indCorr;
       }
     }
 
     public void calculateTorsion() {
       double tors = toDegrees(DoubleMath.dihedralAngle(glyco[0], glyco[1], glyco[2], glyco[3]));
       double delta;
       if (tors > 0) {
         delta = tors - 180.0;
       } else {
         delta = tors + 180.0;
       }
       logger.info(format("restrain-torsion %d %d %d %d  5.000  %f 1", glycoAtomIndex[0], glycoAtomIndex[1], glycoAtomIndex[2], glycoAtomIndex[3], delta));
     }
   }
 }