// ******************************************************************************
   //
   // 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.bonded;
  
  import ffx.potential.bonded.AminoAcidUtils.AminoAcid1;
  import ffx.potential.bonded.AminoAcidUtils.AminoAcid3;
  import ffx.potential.bonded.NucleicAcidUtils.NucleicAcid1;
  import ffx.potential.bonded.NucleicAcidUtils.NucleicAcid3;
  import ffx.potential.parameters.ForceField;
  import ffx.potential.parameters.TitrationUtils;
  import org.jogamp.java3d.Canvas3D;
  import org.jogamp.java3d.J3DGraphics2D;
  import org.jogamp.java3d.Material;
  import org.jogamp.java3d.Node;
  import org.jogamp.vecmath.Color3f;
  import org.jogamp.vecmath.Point2d;
  import org.jogamp.vecmath.Point3d;
  
  import java.io.Serial;
  import java.util.ArrayList;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Objects;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import static ffx.potential.bonded.AminoAcidUtils.AA1toAA3;
  import static ffx.potential.bonded.NucleicAcidUtils.NA1toNA3;
  import static java.lang.System.arraycopy;
  
  /**
   * The Residue class represents individual amino acids or nucleic acid bases.
   *
   * @author Michael J. Schnieders
   * @author Jacob M. Litman
   * @since 1.0
   */
  public class Residue extends MSGroup implements Comparable<Residue> {
  
    @Serial
    private static final long serialVersionUID = 1L;
  
    private static final Logger logger = Logger.getLogger(Residue.class.getName());
    /** Compare residues first on seg ID, then residue number, then residue type, then name. */
    private static final Comparator<Residue> resComparator = Comparator.comparing(Residue::getSegID)
        .thenComparingInt(Residue::getResidueNumber).thenComparing(Residue::getResidueType)
        .thenComparing(Residue::getName);
  
    /** Constant <code>NA3Color</code> */
    private static final HashMap<NucleicAcid3, Color3f> NA3Color = new HashMap<>();
    /** Constant <code>AA3Color</code> */
    private static final HashMap<AminoAcid3, Color3f> AA3Color = new HashMap<>();
    /** Constant <code>SSTypeColor</code> */
    private static final HashMap<SSType, Color3f> SSTypeColor = new HashMap<>();
    /** Constant <code>Ramachandran="new String[17]"</code> */
    public static String[] Ramachandran = new String[17];
  
    private static final Point3d point3d = new Point3d();
    private static final Point2d point2d = new Point2d();
  
    static {
      NA3Color.put(NucleicAcid3.ADE, RendererCache.RED);
      NA3Color.put(NucleicAcid3.CYT, RendererCache.MAGENTA);
     NA3Color.put(NucleicAcid3.GUA, RendererCache.BLUE);
     NA3Color.put(NucleicAcid3.URI, RendererCache.YELLOW);
     NA3Color.put(NucleicAcid3.DAD, RendererCache.RED);
     NA3Color.put(NucleicAcid3.DCY, RendererCache.MAGENTA);
     NA3Color.put(NucleicAcid3.DGU, RendererCache.BLUE);
     NA3Color.put(NucleicAcid3.DTY, RendererCache.ORANGE);
     NA3Color.put(NucleicAcid3.MP1, RendererCache.GREEN);
     NA3Color.put(NucleicAcid3.DP2, RendererCache.GREEN);
     NA3Color.put(NucleicAcid3.TP3, RendererCache.GREEN);
     NA3Color.put(NucleicAcid3.UNK, RendererCache.CYAN);
 
     AA3Color.put(AminoAcid3.ALA, RendererCache.GRAY);
     AA3Color.put(AminoAcid3.ARG, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.ASN, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.ASP, RendererCache.RED);
     AA3Color.put(AminoAcid3.CYS, RendererCache.YELLOW);
     AA3Color.put(AminoAcid3.GLN, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.GLU, RendererCache.RED);
     AA3Color.put(AminoAcid3.GLH, RendererCache.RED);
     AA3Color.put(AminoAcid3.GLD, RendererCache.RED);
     AA3Color.put(AminoAcid3.GLY, RendererCache.GRAY);
     AA3Color.put(AminoAcid3.ILE, RendererCache.GRAY);
     AA3Color.put(AminoAcid3.LEU, RendererCache.GRAY);
     AA3Color.put(AminoAcid3.LYS, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.MET, RendererCache.YELLOW);
     AA3Color.put(AminoAcid3.PHE, RendererCache.GREEN);
     AA3Color.put(AminoAcid3.PRO, RendererCache.ORANGE);
     AA3Color.put(AminoAcid3.SER, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.THR, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.TRP, RendererCache.GREEN);
     AA3Color.put(AminoAcid3.TYR, RendererCache.GREEN);
     AA3Color.put(AminoAcid3.VAL, RendererCache.GRAY);
     AA3Color.put(AminoAcid3.HIS, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.HIE, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.HID, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.ORN, RendererCache.ORANGE);
     AA3Color.put(AminoAcid3.AIB, RendererCache.ORANGE);
     AA3Color.put(AminoAcid3.PCA, RendererCache.ORANGE);
     AA3Color.put(AminoAcid3.FOR, RendererCache.RED);
     AA3Color.put(AminoAcid3.ACE, RendererCache.RED);
     AA3Color.put(AminoAcid3.NH2, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.NME, RendererCache.BLUE);
     AA3Color.put(AminoAcid3.UNK, RendererCache.MAGENTA);
 
     SSTypeColor.put(SSType.NONE, RendererCache.WHITE);
     SSTypeColor.put(SSType.SHEET, RendererCache.PINK);
     SSTypeColor.put(SSType.HELIX, RendererCache.BLUE);
     SSTypeColor.put(SSType.TURN, RendererCache.YELLOW);
 
     Ramachandran[0] = "Default (Extended)       [-135.0  135.0]";
     Ramachandran[1] = "Alpha Helix (R)          [ -57.0  -47.0]";
     Ramachandran[2] = "Alpha Helix (L)          [  57.0   47.0]";
     Ramachandran[3] = "3-10 Helix               [ -49.0  -26.0]";
     Ramachandran[4] = "Pi Helix                 [ -57.0  -70.0]";
     Ramachandran[5] = "Polyproline II Helix     [ -79.0  149.0]";
     Ramachandran[6] = "Parallel Beta Strand     [-119.0  113.0]";
     Ramachandran[7] = "Antiparallel Beta Strand [-139.0  135.0]";
     Ramachandran[8] = "Beta-Hairpin 2' (i+1)    [  90.0 -170.0]";
     Ramachandran[9] = "Beta-Hairpin 2' (i+2)    [ -80.0  -10.0]";
     Ramachandran[10] = "Beta-Hairpin 1' (i+1)    [  57.0   47.0]";
     Ramachandran[11] = "Beta-Hairpin 1' (i+2)    [  57.0   47.0]";
     Ramachandran[12] = "Beta-Hairpin 1  (i+1)    [ -57.0  -47.0]";
     Ramachandran[13] = "Beta-Hairpin 1  (i+2)    [ -57.0  -47.0]";
     Ramachandran[14] = "Beta-Hairpin 1  (i+3)    [  90.0 -170.0]";
     Ramachandran[15] = "Beta-Hairpin 3' (i+1)    [  57.0   47.0]";
     Ramachandran[16] = "Beta-Hairpin 3' (i+2)    [ -80.0  -10.0]";
   }
 
   /** Residue type. */
   ResidueType residueType;
   /** The residue number of this residue in a chain. */
   private int resNumber;
   /** Possibly redundant PDB chain ID. */
   private Character chainID;
   /** Unique segID. */
   private String segID;
   /** The rotamers for this residue. */
   private Rotamer[] rotamers = null;
   /** The current rotamer in use. */
   private Rotamer currentRotamer = null;
   /** Short string describing this residue. */
   private String shortString = null;
   /** 3-letter amino acid code. */
   private AminoAcid3 aa;
   /** 3-letter nucleic acid code. */
   private NucleicAcid3 na;
   /**
    * If this is set, then ASP, GLU, LYS and HIS Rotamers will be titratable.
    */
   private TitrationUtils titrationUtils = null;
   private boolean titrateConformers = false;
 
   public boolean isTitrateConformers() {
     return titrateConformers;
   }
 
   public void setTitrateConformers(boolean titrateConformers) {
     this.titrateConformers = titrateConformers;
   }
 
   public Atom getAtomInitial() {
     return atomInitial;
   }
 
   public void setAtomInitial(Atom atomInitial) {
     this.atomInitial = atomInitial;
   }
 
   private Atom atomInitial;
 
 
 
   /**
    * These arrays store default coordinates for certain atoms in nucleic acid Residues. C1', O4', and
    * C4' are the critical sugar atoms off which every other atom is drawn when applyRotamer is
    * called. The backbone corrections, however, move these atoms, so they must be reverted to their
    * original coordinates each time applyRotamer is called.
    *
    * <p>O3' North and South coordinates are technically non-essential, as they could be derived from
    * C1', O4', C4', and a given sugar pucker, however, it is much less computationally expensive to
    * calculate them once and then store them.
    *
    * <p>TODO: Add O3' coordinates for the DNA C3'-exo configuration.
    */
   private double[] O3sNorthCoords, O3sSouthCoords, C1sCoords, O4sCoords, C4sCoords;
 
   /**
    * Default Constructor where num is this Residue's position in the Polymer.
    *
    * @param num The residue number.
    * @param residueType The residue type.
    */
   public Residue(int num, ResidueType residueType) {
     super();
     resNumber = num;
     this.residueType = residueType;
     assignResidueType();
   }
 
   /**
    * Constructor for Residue.
    *
    * @param name The residue name.
    * @param residueType The residue type.
    */
   public Residue(String name, ResidueType residueType) {
     super(name);
     this.residueType = residueType;
     assignResidueType();
   }
 
   /**
    * Name is the residue's 3 letter abbreviation and num is its position in the Polymer.
    *
    * @param name The residue name.
    * @param num The residue number.
    * @param residueType The residue type.
    */
   public Residue(String name, int num, ResidueType residueType) {
     this(name, residueType);
     resNumber = num;
   }
 
   /**
    * Name is the residue's 3 letter abbreviation and num is its position in the Polymer.
    *
    * @param name The residue name.
    * @param resNumber The residue number.
    * @param residueType The residue type.
    * @param chainID The chain ID.
    * @param segID The segment ID.
    */
   public Residue(String name, int resNumber, ResidueType residueType, Character chainID,
       String segID) {
     this(name, residueType);
     this.resNumber = resNumber;
     this.chainID = chainID;
     this.segID = segID;
   }
 
   /**
    * As above, with atoms being a MSNode with this Residue's atoms as child nodes
    *
    * @param name The residue name.
    * @param resNumber The residue number.
    * @param residueType The residue type.
    * @param atoms a {@link ffx.potential.bonded.MSNode} object.
    * @param forceField the ForceField to use when created bonded terms.
    */
   public Residue(String name, int resNumber, MSNode atoms, ResidueType residueType,
       ForceField forceField) {
     super(name, atoms);
     this.resNumber = resNumber;
     this.residueType = residueType;
     assignResidueType();
     finalize(true, forceField);
   }
 
   @Override
   public void setName(String name) {
     super.setName(name);
     if (residueType != null) {
       assignResidueType();
     }
     for (Atom atom : getAtomList()) {
       atom.setResName(name);
     }
   }
 
   /**
    * {@inheritDoc}
    *
    * <p>Allows adding Atoms to the Residue.
    */
   @Override
   public MSNode addMSNode(MSNode o) {
     Atom currentAtom = null;
     if (o instanceof Atom newAtom) {
       Character newAlt = newAtom.getAltLoc();
       String newName = newAtom.getName().toUpperCase();
       MSNode atoms = getAtomNode();
       currentAtom = (Atom) atoms.contains(newAtom);
       // Check for deuterium
       if (currentAtom == null) {
         if (newName.startsWith("H")) {
           newAtom.setName(newName.replaceFirst("H", "D"));
           currentAtom = (Atom) atoms.contains(newAtom);
           newAtom.setName(newName);
         } else if (newName.startsWith("D")) {
           newAtom.setName(newName.replaceFirst("D", "H"));
           currentAtom = (Atom) atoms.contains(newAtom);
           newAtom.setName(newName);
         }
       }
 
       if (titrateConformers) {
         currentAtom = atomInitial;
         newAtom.setXyzIndex(currentAtom.getXyzIndex());
         atoms.remove(currentAtom);
         currentAtom = newAtom;
         currentAtom.setResName(newAtom.getResidueName());
         currentAtom.setResidueNumber(resNumber);
         atoms.add(currentAtom);
         setFinalized(false);
       } else if (currentAtom == null){
         currentAtom = newAtom;
         currentAtom.setResName(getName());
         currentAtom.setResidueNumber(resNumber);
         atoms.add(newAtom);
         setFinalized(false);
       } else {
         // Allow overwriting of the root alternate conformer (' ' or 'A').
         Character currentAlt = currentAtom.getAltLoc();
         if (currentAlt.equals(' ') || currentAlt.equals('A')) {
           if (!newAlt.equals(' ') && !newAlt.equals('A')) {
             newAtom.setXyzIndex(currentAtom.getXyzIndex());
             atoms.remove(currentAtom);
             currentAtom = newAtom;
             currentAtom.setResName(getName());
             currentAtom.setResidueNumber(resNumber);
             atoms.add(currentAtom);
             setFinalized(false);
           }
         }
       }
     } else {
       logger.warning(" Only an Atom can be added to a Residue.");
     }
     return currentAtom;
   }
 
   @Override
   public int compareTo(Residue o) {
     if (this.equals(o)) {
       return 0;
     }
     return resComparator.compare(this, o);
   }
 
   /** {@inheritDoc} */
   @Override
   public void drawLabel(Canvas3D canvas, J3DGraphics2D g2d, Node node) {
     if (RendererCache.labelResidues) {
       double[] d = getCenter();
       point3d.x = d[0];
       point3d.y = d[1];
       point3d.z = d[2];
       RendererCache.getScreenCoordinate(canvas, node, point3d, point2d);
       g2d.drawString(getName(), (float) point2d.x, (float) point2d.y);
     }
     if (RendererCache.labelAtoms) {
       super.drawLabel(canvas, g2d, node);
     }
   }
 
   /** {@inheritDoc} */
   @Override
   public boolean equals(Object o) {
     if (this == o) {
       return true;
     }
     if (o == null || getClass() != o.getClass()) {
       return false;
     }
     Residue residue = (Residue) o;
     return Objects.equals(segID, residue.segID)
         && Objects.equals(getResidueNumber(), residue.getResidueNumber())
         && residueType == residue.residueType && Objects.equals(getName(), residue.getName());
   }
 
   /**
    * {@inheritDoc}
    *
    * <p>The Finalize method should be called once all atoms have been added to the Residue. Geometry
    * objects (Bonds, Angles, etc) are then formed, followed by a determination of under-constrained
    * (Dangling) atoms.
    */
   @Override
   public void finalize(boolean finalizeGeometry, ForceField forceField) {
     setFinalized(false);
     getAtomNode().setName("Atoms (" + getAtomList().size() + ")");
     if (finalizeGeometry) {
       assignBondedTerms(forceField);
       removeLeaves();
     }
     setCenter(getMultiScaleCenter(false));
     setFinalized(true);
   }
 
   public void setTitrationUtils(TitrationUtils titrationUtils) {
     this.titrationUtils = titrationUtils;
   }
 
   public TitrationUtils getTitrationUtils() {
     return titrationUtils;
   }
 
   /**
    * getAminoAcid3.
    *
    * @return a {@link AminoAcid3} object.
    */
   public AminoAcid3 getAminoAcid3() {
     if (this.residueType != ResidueType.AA) {
       throw new IllegalArgumentException(
           String.format(" This residue is " + "not an amino acid: %s", this));
     }
     return aa;
   }
 
   /**
    * Returns a list of backbone atoms; for our purposes, nucleic acid backbone atoms are those of the
    * nucleobase.
    *
    * @return List of backbone (or nucleobase) atoms.
    */
   public List<Atom> getBackboneAtoms() {
     List<Atom> atoms = getAtomList();
     List<Atom> ret;
     switch (residueType) {
       case NA -> {
         ret = new ArrayList<>(atoms);
         for (Atom atom : atoms) {
           String name = atom.getName().toUpperCase();
           if (name.contains("'") || name.equals("P") || name.startsWith("OP") || name.equals("H5T")
               || name.equals("H3T")) {
             ret.remove(atom);
           }
         }
         return ret;
       }
       case AA -> {
         ret = new ArrayList<>();
         tryAddAtom(ret, "N");
         tryAddAtom(ret, "CA");
         tryAddAtom(ret, "C");
         tryAddAtom(ret, "O");
         tryAddAtom(ret, "OXT"); // C-terminal residues
         tryAddAtom(ret, "OT2"); // Probably alternate name for OXT.
         tryAddAtom(ret, "H1"); // N-terminal residues
         tryAddAtom(ret, "H2");
         tryAddAtom(ret, "H3");
         tryAddAtom(ret, "H");
         tryAddAtom(ret, "HA");
         tryAddAtom(ret, "HA2"); // Glycines
         tryAddAtom(ret, "HA3");
         return ret;
       }
       default -> {
         return new ArrayList<>(1); // Return empty list.
       }
     }
   }
 
   /**
    * Returns this Residues Parent Polymer name.
    *
    * @return a {@link java.lang.Character} object.
    */
   public Character getChainID() {
     return chainID;
   }
 
   /**
    * Setter for the field <code>chainID</code>.
    *
    * @param c a {@link java.lang.Character} object.
    */
   public void setChainID(Character c) {
     chainID = c;
 
     for (Atom atom : getAtomList()) {
       atom.setChainID(c);
     }
   }
 
   /**
    * Setter for the field <code>segID</code>.
    *
    * @param segID The segID to use.
    */
   public void setSegID(String segID) {
     this.segID = segID;
 
     for (Atom atom : getAtomList()) {
       atom.setSegID(segID);
     }
   }
 
   /**
    * Returns the Residue bonded to this Residue at this Residue's 3' or C-terminal end. Any use of
    * this method to add Residues to a sliding window or similar MUST not add that residue if that
    * residue has no Rotamers, as several algorithms (such as the distance matrix) assume that all
    * Residues being optimized have Rotamers.
    *
    * @return The next Residue.
    */
   public Residue getNextResidue() {
     switch (residueType) {
       case AA -> {
         Atom carbon = (Atom) getAtomNode("C");
         if (carbon == null) {
           return null;
         }
         List<Bond> bonds = carbon.getBonds();
         for (Bond b : bonds) {
           Atom other = b.get1_2(carbon);
           if (other.getName().equalsIgnoreCase("N")) {
             return (Residue) other.getParent().getParent();
           }
         }
       }
       case NA -> {
         Atom oxygen = (Atom) getAtomNode("O3'");
         if (oxygen == null) {
           return null;
         }
         List<Bond> bonds = oxygen.getBonds();
         for (Bond b : bonds) {
           Atom other = b.get1_2(oxygen);
           if (other.getName().equalsIgnoreCase("P")) {
             return (Residue) other.getParent().getParent();
           }
         }
       }
       default -> {
         return null;
       }
     }
     return null;
     // Will generally indicate that you passed in a chain-terminal residue.
   }
 
   /**
    * getNucleicAcid3.
    *
    * @return a {@link NucleicAcid3} object.
    */
   public NucleicAcid3 getNucleicAcid3() {
     if (this.residueType != ResidueType.NA) {
       throw new IllegalArgumentException(
           String.format(" This residue is not a nucleic acid: %s", this));
     }
     return na;
   }
 
   /**
    * Returns the NucleicAcid3 corresponding to this Residue, with additional robust checking for 1-
    * or 2-letter names.
    *
    * @param matchShortName Try to match 1- or 2-letter names (e.g. A to ADE).
    * @return a {@link NucleicAcid3} object.
    */
   public NucleicAcid3 getNucleicAcid3(boolean matchShortName) {
     NucleicAcid3 na3 = getNucleicAcid3();
     if (na3 == NucleicAcidUtils.NucleicAcid3.UNK && matchShortName) {
       switch (getName()) {
         case "A" -> {
           return NucleicAcid3.ADE;
         }
         case "C" -> {
           return NucleicAcid3.CYT;
         }
         case "G" -> {
           return NucleicAcid3.GUA;
         }
         case "T" -> {
           return NucleicAcid3.THY;
         }
         case "U" -> {
           return NucleicAcid3.URI;
         }
         case "DA" -> {
           return NucleicAcid3.DAD;
         }
         case "DC" -> {
           return NucleicAcid3.DCY;
         }
         case "DG" -> {
           return NucleicAcid3.DGU;
         }
         case "DT" -> {
           return NucleicAcid3.DTY;
         }
         case "DU" -> throw new IllegalArgumentException(
             " No NucleicAcid3 enum exists for DU (presumed to be deoxy-uracil)!");
       }
     }
     return na3;
   }
 
   /**
    * Returns the Residue bonded to this Residue at this Residue's 5' or N-terminal end. Any use of
    * this method to add Residues to a sliding window or similar MUST not add that residue if that
    * residue has no Rotamers, as several algorithms (such as the distance matrix) assume that all
    * Residues being optimized have Rotamers.
    *
    * @return The previous Residue.
    */
   public Residue getPreviousResidue() {
     switch (residueType) {
       case AA -> {
         Atom nitrogen = (Atom) getAtomNode("N");
         if (nitrogen == null) {
           return null;
         }
         List<Bond> bonds = nitrogen.getBonds();
         for (Bond b : bonds) {
           Atom other = b.get1_2(nitrogen);
           if (other.getName().equalsIgnoreCase("C")) {
             return (Residue) other.getParent().getParent();
           }
         }
       }
       case NA -> {
         Atom phosphate = (Atom) getAtomNode("P");
         if (phosphate == null) {
           return null;
         }
         List<Bond> bonds = phosphate.getBonds();
         for (Bond b : bonds) {
           Atom other = b.get1_2(phosphate);
           if (other.getName().equalsIgnoreCase("O3'")) {
             return (Residue) other.getParent().getParent();
           }
         }
       }
       default -> {
         return null;
       }
     }
     return null;
     // Will generally indicate that you passed in a chain-starting residue.
   }
 
   /**
    * Returns a reference Atom for a Residue, primarily intended for rough distance calculations. This
    * atom should be roughly centrally located within the residue, and be invariant.
    *
    * @return A reference Atom.
    */
   public Atom getReferenceAtom() {
     Atom atom = null;
     switch (this.getResidueType()) {
       case AA -> atom = (Atom) this.getAtomNode("CA");
       case NA -> {
         // If pyrimidine, atom will be N1.  Else, if purine,
         // N1 will return null, so grab N9.
         atom = (Atom) this.getAtomNode("N1");
         if (atom == null) {
           atom = (Atom) this.getAtomNode("N9");
         }
       }
       default -> {
       }
     }
     if (atom == null) {
       atom = (Atom) this.getAtomNode(0);
     }
     return atom;
   }
 
   /**
    * Returns this Residue's sequence number.
    *
    * @return The sequence number.
    */
   public int getResidueNumber() {
     return resNumber;
   }
 
   /**
    * Getter for the field <code>residueType</code>.
    *
    * @return a {@link ResidueType} object.
    */
   public ResidueType getResidueType() {
     return residueType;
   }
 
   /**
    * Get the current rotamer.
    *
    * @return a {@link ffx.potential.bonded.Rotamer} object.
    */
   public Rotamer getRotamer() {
     return currentRotamer;
   }
 
   /**
    * Set the current rotamer.
    *
    * @param rotamer a {@link ffx.potential.bonded.Rotamer} object.
    */
   public void setRotamer(Rotamer rotamer) {
     this.currentRotamer = rotamer;
   }
 
   /**
    * Return all currently set rotamers.
    *
    * @return All current rotamers for this residue.
    */
   public Rotamer[] getRotamers() {
     return rotamers;
   }
 
   /**
    * Resets the rotamers for this residue, potentially incorporating the original coordinates if
    * RotamerLibrary's original coordinates rotamer flag has been set.
    * <p>
    * Any rotamers that were set previously are deleted.
    *
    * @param library Rotamer library to use
    * @return An array of Rotamer.
    */
   public Rotamer[] setRotamers(RotamerLibrary library) {
 
     // Obtain rotamers for this residue from the RotamerLibrary.
     Rotamer[] libRotamers = library.getRotamers(this, titrationUtils);
     rotamers = libRotamers;
 
     // Add the original coordinates as a rotamer if requested
     // (unless the library has no rotamers for this residue).
     if (library.getUsingOrigCoordsRotamer() && rotamers != null) {
       // Define the current coordinates as a new rotamer.
       Rotamer[] originalRotamers = Rotamer.defaultRotamerFactory(this, titrationUtils);
       int nOrig = originalRotamers.length;
       // Add the original rotamers to those from the library and cache the result.
       int libRots = libRotamers.length;
       rotamers = new Rotamer[libRots + nOrig];
       // First rotamers are the original conformation.
       arraycopy(originalRotamers, 0, rotamers, 0, nOrig);
       // Copy in the library.
       arraycopy(libRotamers, 0, rotamers, nOrig, libRots);
     }
 
     return rotamers;
   }
 
   /**
    * Sets the original coordinate rotamers for titratable residues
    * RotamerLibrary's original coordinates rotamer flag has been set.
    * <p>
    * Any rotamers that were set previously are deleted.
    *
    * @return An array of Rotamer.
    */
   public Rotamer[] setRotamers(){
     Rotamer[] originalRotamers = Rotamer.defaultRotamerFactory(this, titrationUtils);
     int nOrig = originalRotamers.length;
     rotamers = new Rotamer[nOrig];
     arraycopy(originalRotamers, 0, rotamers, 0, nOrig);
     return rotamers;
   }
 
   /**
    * Getter for the field <code>segID</code>.
    *
    * @return a {@link java.lang.String} object.
    */
   public String getSegID() {
     return segID;
   }
 
   /**
    * Returns a list of side chain atoms; for our purposes, nucleic acid side chain atoms are the
    * sugar and the phosphate.
    *
    * @return List of side chain (or nucleic backbone) atoms.
    */
   public List<Atom> getSideChainAtoms() {
     List<Atom> atoms = getAtomList();
     List<Atom> ret;
     switch (residueType) {
       case NA -> {
         ret = new ArrayList<>();
         for (Atom atom : atoms) {
           String name = atom.getName().toUpperCase();
           /*
            * Very conveniently for our purposes, the entire sugar is
            * denoted with ' at the end. Note that we add the side chain
            * atoms for NAs, instead of removing the backbone.
            */
           if (name.contains("'") || name.equals("P") || name.startsWith("OP")) {
             ret.add(atom);
           }
         }
         return ret;
       }
       case AA -> {
         ret = new ArrayList<>(atoms);
         for (Atom atom : atoms) {
           String name = atom.getName().toUpperCase();
           if (name.equals("N") || name.equals("H") || name.equals("H1") || name.equals("H2")
               || name.equals("H3") || name.equals("CA") || name.startsWith("HA") || name.equals("C")
               || name.equals("O") || name.equals("OXT") || name.equals("OT2")) {
             ret.remove(atom);
           }
         }
         return ret;
       }
       default -> {
         return null;
       }
     }
   }
 
   /**
    * Returns a list of atoms liable to change during dead-end elimination repacking. For ordinary
    * amino acids: side chain atoms. For ordinary nucleic acids: sugar/phosphate backbone atoms.
    * MultiResidue over-rides this to return all atoms (as backbone atom types are non-constant).
    *
    * @return Atoms changeable during DEE.
    */
   public List<Atom> getVariableAtoms() {
     return getSideChainAtoms();
   }
 
   /** {@inheritDoc} */
   @Override
   public int hashCode() {
     return Objects.hash(segID, getResidueNumber(), residueType, getName());
   }
 
   /**
    * Initializes this (presumably nucleic acid) Residue's C1s, O4s, C4s, O3sNorth, and O3sSouth
    * default coordinates based on default PDB atom locations; to preserve rotamer independence, this
    * must be called before any NA rotamers are applied.
    */
   public void initializeDefaultAtomicCoordinates() {
     if (residueType != ResidueType.NA) {
       return;
     }
     boolean isDeoxy;
     try {
       isDeoxy = switch (NucleicAcid3.valueOf(this.getName())) {
         case DAD, DCY, DGU, DTY -> true;
         default -> false;
       };
       C1sCoords = new double[3];
       ((Atom) getAtomNode("C1'")).getXYZ(C1sCoords);
       O4sCoords = new double[3];
       ((Atom) getAtomNode("O4'")).getXYZ(O4sCoords);
       C4sCoords = new double[3];
       ((Atom) getAtomNode("C4'")).getXYZ(C4sCoords);
 
       /*
        With the place flag set false, applySugarPucker returns
        hypothetical O3' coordinates based on default atom positions and
        the supplied sugar pucker.
       */
       O3sNorthCoords = RotamerLibrary.applySugarPucker(this,
           RotamerLibrary.NucleicSugarPucker.C3_ENDO, isDeoxy, false);
       O3sSouthCoords = RotamerLibrary.applySugarPucker(this,
           RotamerLibrary.NucleicSugarPucker.C2_ENDO, isDeoxy, false);
     } catch (Exception e) {
       logger.log(Level.WARNING, toString(), e);
     }
   }
 
   /**
    * {@inheritDoc}
    *
    * <p>Prints "Residue Number: x" to stdout.
    */
   @Override
   public void print() {
     logger.info(" " + this);
     for (Atom a : getAtomNode().getAtomList()) {
       a.print();
     }
   }
 
   /**
    * revertState.
    *
    * @param state a {@link ffx.potential.bonded.ResidueState} object.
    */
   public void revertState(ResidueState state) {
     List<Atom> atomList = getAtomList();
     for (Atom atom : atomList) {
       atom.moveTo(state.getAtomCoords(atom));
     }
   }
 
   /** {@inheritDoc} */
   @Override
   public void setColor(RendererCache.ColorModel newColorModel, Color3f color, Material mat) {
     // If Color by Residue, pass this Residue's Color
     if (newColorModel == RendererCache.ColorModel.RESIDUE) {
       switch (residueType) {
         case AA -> color = AA3Color.get(aa);
         case NA -> color = NA3Color.get(na);
         default -> color = null;
       }
       if (color == null) {
         return;
       }
       mat = RendererCache.materialFactory(color);
     } else if (newColorModel == RendererCache.ColorModel.STRUCTURE) {
       color = SSTypeColor.get(SSType.NONE);
       mat = RendererCache.materialFactory(color);
     }
     super.setColor(newColorModel, color, mat);
   }
 
   /**
    * setNumber
    *
    * @param n The residue number.
    */
   public void setNumber(int n) {
     resNumber = n;
     for (Atom atom : getAtomList()) {
       atom.setResidueNumber(n);
     }
   }
 
   /**
    * Returns the coordinates of all atoms in this Residue as a 2D array.
    *
    * @return the coordinates of all atoms in this Residue as a 2D array.
    */
   public double[][] storeCoordinateArray() {
     List<Atom> atomList = getAtomList();
     int nAtoms = atomList.size();
     double[][] coords = new double[nAtoms][3];
     int i = 0;
     for (Atom atom : atomList) {
       atom.getXYZ(coords[i++]);
     }
     return coords;
   }
 
   /**
    * storeState.
    *
    * @return a {@link ffx.potential.bonded.ResidueState} object.
    */
   public ResidueState storeState() {
     return new ResidueState(this, this);
   }
 
   /**
    * Formats this residue with some optional inclusions.
    *
    * <p>[residue type]-[chain ID]ResNumber-Name.
    *
    * @param addResType Include the residue type
    * @param addChainID Include the chain ID.
    * @return A descriptive string.
    */
   public String toFormattedString(boolean addResType, boolean addChainID) {
     StringBuilder sb = new StringBuilder();
     if (addResType) {
       sb.append(residueType.toString()).append("-");
     }
     if (addChainID) {
       sb.append(chainID);
     }
     sb.append(this);
     return sb.toString();
   }
 
   /**
    * A descriptive string based on a given rotamer.
    *
    * <p>[chain ID]ResNumber-RotamerName.
    *
    * @param rotamer The rotamer to use.
    * @return A descriptive string.
    */
   public String toString(Rotamer rotamer) {
     return "" + chainID + resNumber + "-" + rotamer.getName();
   }
 
   /** {@inheritDoc} */
   @Override
   public String toString() {
     if (shortString == null) {
       shortString = resNumber + "-" + getName();
     }
     return shortString;
   }
 
   /**
    * Add an array of rotamers to this Residue's cached array of rotamers.
    *
    * @param rotamers The rotamers to add.
    */
   void addRotamers(Rotamer[] rotamers) {
     for (Rotamer rotamer : rotamers) {
       addRotamer(rotamer);
     }
   }
 
   /**
    * Add a rotamer to this Residue's cached array of rotamers.
    *
    * @param rotamer The rotamer to add.
    */
   void addRotamer(Rotamer rotamer) {
     if (rotamers != null) {
       Rotamer[] libRotamers = rotamers;
       int nRots = libRotamers.length;
       rotamers = new Rotamer[nRots + 1];
       arraycopy(libRotamers, 0, rotamers, 0, nRots);
       rotamers[rotamers.length - 1] = rotamer;
     } else {
       rotamers = new Rotamer[1];
       rotamers[0] = rotamer;
     }
   }
 
   /**
    * deleteAtom
    *
    * @param atomToDelete a {@link ffx.potential.bonded.Atom} object.
    */
   void deleteAtom(Atom atomToDelete) {
     MSNode atoms = getAtomNode();
     if (atoms.contains(atomToDelete) != null) {
       logger.info(" The following atom is being deleted from the model:\n" + atomToDelete);
       atoms.remove(atomToDelete);
     }
   }
 
   /**
    * Returns the position of this (presumably nucleic acid) Residue's default O3' coordinates given a
    * North pucker.
    *
    * @return a new double[] with default XYZ coordinates for O3' in a North pucker.
    */
   double[] getO3sNorth() {
     double[] ret = new double[3];
     arraycopy(O3sNorthCoords, 0, ret, 0, ret.length);
     return ret;
   }
 
   /**
    * Returns the position of this (presumably nucleic acid) Residue's default O3' coordinates given a
    * South pucker.
    *
    * @return a new double[] with default XYZ coordinates for O3' in a South pucker.
    */
   double[] getO3sSouth() {
     double[] ret = new double[3];
     arraycopy(O3sSouthCoords, 0, ret, 0, ret.length);
     return ret;
   }
 
   /**
    * Returns the position of this (presumably nucleic acid) Residue's original C1' coordinates.
    *
    * @return a new double[] with original XYZ coordinates for C1'.
    */
   double[] getC1sCoords() {
     double[] ret = new double[3];
     arraycopy(C1sCoords, 0, ret, 0, ret.length);
     return ret;
   }
 
   /**
    * Returns the position of this (presumably nucleic acid) Residue's original O4' coordinates.
    *
    * @return a new double[] with original XYZ coordinates for O4'.
    */
   double[] getO4sCoords() {
     double[] ret = new double[3];
     arraycopy(O4sCoords, 0, ret, 0, ret.length);
     return ret;
   }
 
   /**
    * Returns the position of this (presumably nucleic acid) Residue's original C4' coordinates.
    *
    * @return a new double[] with original XYZ coordinates for C4'.
    */
   double[] getC4sCoords() {
     double[] ret = new double[3];
     arraycopy(C4sCoords, 0, ret, 0, ret.length);
     return ret;
   }
 
   /**
    * Uses a name to add an Atom to a List<Atom> if the Atom exists for this residue.
    *
    * @param atList List to add to.
    * @param name Atom to add.
    * @return If atom exists.
    */
   private boolean tryAddAtom(List<Atom> atList, String name) {
     try {
       Atom at = (Atom) getAtomNode(name);
       if (at != null) {
         atList.add(at);
         return true;
       } else {
         return false;
       }
     } catch (Exception ex) {
       return false;
     }
   }
 
   private void assignResidueType() {
     String name = getName().toUpperCase();
     switch (residueType) {
       case AA -> {
         aa = null;
         try {
           if (name.length() >= 2) {
             aa = AminoAcid3.valueOf(name);
           } else if (name.length() == 1) {
             AminoAcid1 aa1 = AminoAcid1.valueOf(name);
             aa = AA1toAA3.get(aa1);
           }
         } catch (Exception e) {
           logger.fine(String.format("Exception assigning AA3 for residue: %s", name));
           aa = AminoAcid3.UNK;
         }
       }
       case NA -> {
         na = null;
         try {
           if (name.length() >= 2) {
             na = NucleicAcid3.parse(name);
           } else if (name.length() == 1) {
             NucleicAcid1 na1 = NucleicAcid1.valueOf(name);
             na = NA1toNA3.get(na1);
           }
         } catch (Exception e) {
           na = NucleicAcid3.UNK;
         }
       }
     }
   }
 
   public enum SSType {
     NONE, HELIX, SHEET, TURN
   }
 
   /**
    * Residue type [NA, AA, UNK].
    */
   public enum ResidueType {
     NA, AA, UNK
   }
 }