// ******************************************************************************
   //
   // 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.openmm;
  
  import ffx.crystal.Crystal;
  import ffx.numerics.switching.UnivariateSwitchingFunction;
  import ffx.potential.DualTopologyEnergy;
  import ffx.potential.ForceFieldEnergy;
  import ffx.potential.MolecularAssembly;
  import ffx.potential.Platform;
  import ffx.potential.bonded.Atom;
  import ffx.potential.parameters.ForceField;
  import ffx.potential.utils.EnergyException;
  
  import javax.annotation.Nullable;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_State_DataType.OpenMM_State_Energy;
  import static java.lang.Double.isFinite;
  import static java.lang.String.format;
  
  public class OpenMMDualTopologyEnergy extends DualTopologyEnergy implements OpenMMPotential {
  
    private static final Logger logger = Logger.getLogger(OpenMMDualTopologyEnergy.class.getName());
  
    /**
     * OpenMM Context.
     */
    private final OpenMMContext openMMContext;
    /**
     * OpenMMDualTopologySystem.
     */
    private final OpenMMDualTopologySystem openMMDualTopologySystem;
    /**
     * The atoms this OpenMMEnergy operates on.
     */
    private final Atom[] atoms;
    /**
     * MolecularAssembly for topology 1.
     */
    private final MolecularAssembly molecularAssembly1;
    /**
     * MolecularAssembly for topology 2.
     */
    private final MolecularAssembly molecularAssembly2;
  
    /**
     * Constructor for DualTopologyEnergy.
     *
     * @param topology1         a {@link MolecularAssembly} object.
     * @param topology2         a {@link MolecularAssembly} object.
     * @param switchFunction    a {@link UnivariateSwitchingFunction} object.
     * @param requestedPlatform a {@link Platform} object.
     */
    public OpenMMDualTopologyEnergy(MolecularAssembly topology1, MolecularAssembly topology2,
                                    UnivariateSwitchingFunction switchFunction, Platform requestedPlatform) {
      super(topology1, topology2, switchFunction);
  
      logger.info("\n Initializing an OpenMM Dual Topology System.");
  
      molecularAssembly1 = topology1;
      molecularAssembly2 = topology2;
  
     // Check that the two topologies do not use symmetry operators.
     Crystal crystal1 = molecularAssembly1.getCrystal();
     int symOps1 = crystal1.spaceGroup.getNumberOfSymOps();
     Crystal crystal2 = molecularAssembly2.getCrystal();
     int symOps2 = crystal2.spaceGroup.getNumberOfSymOps();
     if (symOps1 > 1 || symOps2 > 1) {
       logger.severe(" OpenMM does not support symmetry operators.");
     }
 
     // Load the OpenMM plugins
     ForceField forceField = topology1.getForceField();
     ffx.openmm.Platform openMMPlatform = OpenMMContext.loadPlatform(requestedPlatform, forceField);
 
     // Create the OpenMM System.
     openMMDualTopologySystem = new OpenMMDualTopologySystem(this);
     openMMDualTopologySystem.addForces();
 
     atoms = getDualTopologyAtoms(0);
 
     // Create the Context.
     openMMContext = new OpenMMContext(openMMPlatform, openMMDualTopologySystem, atoms);
   }
 
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double energy(double[] x) {
     return energy(x, false);
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public double energy(double[] x, boolean verbose) {
     // Make sure the context has been created.
     openMMContext.update();
 
     updateParameters(atoms);
 
     // Unscale and set the coordinates.
     unscaleCoordinates(x);
     setCoordinates(x);
 
     OpenMMState openMMState = openMMContext.getOpenMMState(OpenMM_State_Energy);
     double e = openMMState.potentialEnergy;
     openMMState.destroy();
 
     if (!isFinite(e)) {
       String message = format(" OpenMMDualTopologyEnergy was a non-finite %8g", e);
       logger.warning(message);
       throw new EnergyException(message);
     }
 
     if (verbose) {
       logger.log(Level.INFO, format("\n OpenMM Energy: %14.10g", e));
     }
 
     return e;
   }
 
   /**
    * Compute the energy using the pure Java code path.
    *
    * @param x Atomic coordinates.
    * @return The energy (kcal/mol)
    */
   public double energyFFX(double[] x) {
     return super.energy(x, false);
   }
 
   /**
    * Compute the energy using the pure Java code path.
    *
    * @param x       Input atomic coordinates
    * @param verbose Use verbose logging.
    * @return The energy (kcal/mol)
    */
   public double energyFFX(double[] x, boolean verbose) {
     return super.energy(x, verbose);
   }
 
 
   /**
    * Coordinates for active atoms in units of Angstroms.
    *
    * @param x Atomic coordinates active atoms.
    */
   @Override
   public void setCoordinates(double[] x) {
     // Load the coordinates for active atoms.
     super.setCoordinates(x);
 
     int n = atoms.length * 3;
     double[] xall = new double[n];
     int i = 0;
     for (Atom atom : atoms) {
       xall[i] = atom.getX();
       xall[i + 1] = atom.getY();
       xall[i + 2] = atom.getZ();
       i += 3;
     }
 
     // Load OpenMM coordinates for all atoms.
     openMMContext.setPositions(xall);
   }
 
   /**
    * Velocities for active atoms in units of Angstroms.
    *
    * @param v Velocities for active atoms.
    */
   @Override
   public void setVelocity(double[] v) {
     // Load the velocity for active atoms.
     super.setVelocity(v);
 
     int n = atoms.length * 3;
     double[] vall = new double[n];
     double[] v3 = new double[3];
     int i = 0;
     for (Atom atom : atoms) {
       atom.getVelocity(v3);
       // If the atom is not active, set its velocity to zero.
       if (!atom.isActive()) {
         v3[0] = 0.0;
         v3[1] = 0.0;
         v3[2] = 0.0;
         atom.setVelocity(v3);
       }
       vall[i] = v3[0];
       vall[i + 1] = v3[1];
       vall[i + 2] = v3[2];
       i += 3;
     }
 
     // Load OpenMM velocities for all atoms.
     openMMContext.setVelocities(vall);
   }
 
 
   /**
    * Get the MolecularAssembly.
    *
    * @param topology The topology index (0 for topology 1, 1 for topology 2).
    * @return a {@link MolecularAssembly} object for topology 1.
    */
   public MolecularAssembly getMolecularAssembly(int topology) {
     if (topology == 0) {
       return molecularAssembly1;
     } else if (topology == 1) {
       return molecularAssembly2;
     } else {
       throw new IllegalArgumentException(" Invalid topology index: " + topology);
     }
   }
 
   /**
    * Get the OpenMMEnergy for the specified topology.
    *
    * @param topology The topology index (0 for topology 1, 1 for topology 2).
    * @return The OpenMMEnergy for the specified topology.
    */
   public ForceFieldEnergy getForceFieldEnergy(int topology) {
     if (topology == 0) {
       return getForceFieldEnergy1();
     } else if (topology == 1) {
       return getForceFieldEnergy2();
     } else {
       throw new IllegalArgumentException(" Invalid topology index: " + topology);
     }
   }
 
   /**
    * Update parameters if the Use flags and/or Lambda value has changed.
    *
    * @param atoms Atoms in this list are considered.
    */
   @Override
   public void updateParameters(@Nullable Atom[] atoms) {
     if (atoms == null) {
       atoms = this.atoms;
     }
     if (openMMDualTopologySystem != null) {
       openMMDualTopologySystem.updateParameters(atoms);
     }
   }
 
   /**
    * Returns the Context instance.
    *
    * @return context
    */
   @Override
   public OpenMMContext getContext() {
     return openMMContext;
   }
 
   /**
    * Create an OpenMM Context.
    *
    * <p>Context.free() must be called to free OpenMM memory.
    *
    * @param integratorName Integrator to use.
    * @param timeStep       Time step.
    * @param temperature    Temperature (K).
    * @param forceCreation  Force a new Context to be created, even if the existing one matches the
    *                       request.
    */
   @Override
   public void updateContext(String integratorName, double timeStep, double temperature, boolean forceCreation) {
     openMMContext.update(integratorName, timeStep, temperature, forceCreation);
   }
 
   /**
    * Create an immutable OpenMM State.
    *
    * <p>State.free() must be called to free OpenMM memory.
    *
    * @param mask The State mask.
    * @return Returns the State.
    */
   @Override
   public OpenMMState getOpenMMState(int mask) {
     return openMMContext.getOpenMMState(mask);
   }
 
   /**
    * Get a reference to the System instance.
    *
    * @return a reference to the OpenMMSystem.
    */
   @Override
   public OpenMMSystem getSystem() {
     return openMMDualTopologySystem;
   }
 
   /**
    * Update active atoms.
    */
   @Override
   public boolean setActiveAtoms() {
     return openMMDualTopologySystem.updateAtomMass();
   }
 
 }