// ******************************************************************************
   //
   // 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.
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  // 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
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  // permission to link this library with independent modules to produce an
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  package ffx.algorithms.optimize;
  
  import static java.lang.String.format;
  import static java.util.Arrays.fill;
  
  import ffx.algorithms.AlgorithmListener;
  import ffx.algorithms.Terminatable;
  import ffx.algorithms.dynamics.MolecularDynamics;
  import ffx.algorithms.dynamics.MDEngine;
  import ffx.numerics.Potential;
  import ffx.numerics.optimization.LBFGS;
  import ffx.numerics.optimization.LineSearch;
  import ffx.numerics.optimization.OptimizationListener;
  import ffx.potential.ForceFieldEnergy;
  import ffx.potential.Platform;
  import ffx.potential.openmm.OpenMMEnergy;
  import ffx.potential.MolecularAssembly;
  
  import java.util.EnumSet;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  import org.apache.commons.configuration2.CompositeConfiguration;
  
  /**
   * Minimize the potential energy of a system to an RMS gradient per atom convergence criteria.
   *
   * @author Michael J. Schnieders
   * @since 1.0
   */
  public class Minimize implements OptimizationListener, Terminatable {
  
    private static final Logger logger = Logger.getLogger(Minimize.class.getName());
  
    /**
     * The MolecularAssembly being operated on.
     */
    protected final MolecularAssembly molecularAssembly;
    /**
     * The potential energy to optimize.
     */
    protected final Potential potential;
    /**
     * The AlgorithmListener to update the UI.
     */
    protected final AlgorithmListener algorithmListener;
    /**
     * Number of variables.
     */
    protected final int n;
    /**
     * Current value of each variable.
     */
    protected final double[] x;
    /**
     * The gradient.
     */
    protected final double[] grad;
    /**
     * Scaling applied to each variable.
     */
    protected final double[] scaling;
   /**
    * A flag to indicate the algorithm is done.
    */
   protected boolean done = false;
   /**
    * A flag to indicate the algorithm should be terminated.
    */
   protected boolean terminate = false;
   /**
    * Minimization time in nanoseconds.
    */
   protected long time;
   /**
    * The final potential energy.
    */
   protected double energy;
   /**
    * The return status of the optimization.
    */
   protected int status;
   /**
    * The number of optimization steps taken.
    */
   protected int nSteps;
   /**
    * The final RMS gradient.
    */
   double rmsGradient;
 
   /**
    * The default number of correction vectors used by the limited-memory L-BFGS optimization
    * routine.
    * <p>
    * Values of less than 3 are not recommended and large values will result in excessive computing
    * time. The range from <code>3 &lt;= mSave &lt;= 7</code> is recommended.
    */
   public static final int DEFAULT_LBFGS_VECTORS = 7;
 
   /**
    * Constructor for Minimize.
    *
    * @param molecularAssembly a {@link ffx.potential.MolecularAssembly} object.
    * @param potential         a {@link ffx.numerics.Potential} object.
    * @param algorithmListener a {@link ffx.algorithms.AlgorithmListener} object.
    */
   public Minimize(MolecularAssembly molecularAssembly, Potential potential,
                   AlgorithmListener algorithmListener) {
     this.molecularAssembly = molecularAssembly;
     this.algorithmListener = algorithmListener;
     this.potential = potential;
     n = potential.getNumberOfVariables();
     x = new double[n];
     grad = new double[n];
     scaling = new double[n];
     fill(scaling, 12.0);
   }
 
   /**
    * Constructor for Minimize.
    *
    * @param molecularAssembly a {@link ffx.potential.MolecularAssembly} object.
    * @param algorithmListener a {@link ffx.algorithms.AlgorithmListener} object.
    */
   public Minimize(MolecularAssembly molecularAssembly, AlgorithmListener algorithmListener) {
     this.molecularAssembly = molecularAssembly;
     this.algorithmListener = algorithmListener;
     if (molecularAssembly.getPotentialEnergy() == null) {
       molecularAssembly.setPotential(ForceFieldEnergy.energyFactory(molecularAssembly));
     }
     potential = molecularAssembly.getPotentialEnergy();
     n = potential.getNumberOfVariables();
     x = new double[n];
     grad = new double[n];
     scaling = new double[n];
     fill(scaling, 12.0);
   }
 
   public static MinimizationEngine defaultEngine(MolecularAssembly molecularAssembly,
                                                  Potential potentialEnergy) {
     CompositeConfiguration properties = molecularAssembly.getProperties();
     String minimizeEngine = properties.getString("minimize-engine", null);
     if (minimizeEngine != null) {
       if (minimizeEngine.equalsIgnoreCase("OMM")) {
         return MinimizationEngine.OPENMM;
       } else {
         return MinimizationEngine.FFX;
       }
     } else {
       if (potentialEnergy instanceof OpenMMEnergy) {
         return MinimizationEngine.OPENMM;
       } else {
         return MinimizationEngine.FFX;
       }
     }
   }
 
   /**
    * dynamicsFactory.
    *
    * @param assembly        a {@link ffx.potential.MolecularAssembly} object.
    * @param potentialEnergy a {@link ffx.numerics.Potential} object.
    * @param listener        a {@link ffx.algorithms.AlgorithmListener} object.
    * @param engine          a {@link MDEngine} object.
    * @return a {@link MolecularDynamics} object.
    */
   public static Minimize minimizeFactory(MolecularAssembly assembly, Potential potentialEnergy,
                                          AlgorithmListener listener, MinimizationEngine engine) {
     return switch (engine) {
       case OPENMM -> new MinimizeOpenMM(assembly, (OpenMMEnergy) potentialEnergy, listener);
       default -> new Minimize(assembly, potentialEnergy, listener);
     };
   }
 
   /**
    * Getter for the field <code>energy</code>.
    *
    * @return a double.
    */
   public double getEnergy() {
     return energy;
   }
 
   /**
    * getRMSGradient.
    *
    * @return a double.
    */
   public double getRMSGradient() {
     return rmsGradient;
   }
 
   /**
    * Getter for the field <code>status</code>.
    *
    * @return The status of the optimization.
    */
   public int getStatus() {
     return status;
   }
 
   /**
    * Getter for the number of iterations completed this minimization.
    *
    * @return The number of iterations
    */
   public int getIterations() {
     return nSteps;
   }
 
   /**
    * minimize
    *
    * @return a {@link ffx.numerics.Potential} object.
    */
   public Potential minimize() {
     return minimize(DEFAULT_LBFGS_VECTORS, 1.0, Integer.MAX_VALUE);
   }
 
   /**
    * minimize
    *
    * @param eps The convergence criteria.
    * @return a {@link ffx.numerics.Potential} object.
    */
   public Potential minimize(double eps) {
     return minimize(DEFAULT_LBFGS_VECTORS, eps, Integer.MAX_VALUE);
   }
 
   /**
    * minimize
    *
    * @param eps           The convergence criteria.
    * @param maxIterations The maximum number of iterations.
    * @return a {@link ffx.numerics.Potential} object.
    */
   public Potential minimize(double eps, int maxIterations) {
     return minimize(DEFAULT_LBFGS_VECTORS, eps, maxIterations);
   }
 
   /**
    * minimize
    *
    * @param m             The number of previous steps used to estimate the Hessian.
    * @param eps           The convergence criteria.
    * @param maxIterations The maximum number of iterations.
    * @return a {@link ffx.numerics.Potential} object.
    */
   public Potential minimize(int m, double eps, int maxIterations) {
     time = System.nanoTime();
     potential.getCoordinates(x);
     potential.setScaling(scaling);
 
     // Scale coordinates.
     for (int i = 0; i < n; i++) {
       x[i] *= scaling[i];
     }
 
     done = false;
     energy = potential.energyAndGradient(x, grad);
 
     if (logger.isLoggable(Level.FINE)) {
       logger.fine(format(" Minimize initial energy: %16.8f", energy));
     }
 
     status = LBFGS.minimize(n, m, x, energy, grad, eps, maxIterations, potential, this);
     done = true;
 
     switch (status) {
       case 0 -> logger.info(format("\n Optimization achieved convergence criteria: %8.5f", rmsGradient));
       case 1 -> logger.info(format("\n Optimization terminated at step %d.", nSteps));
       default -> logger.warning("\n Optimization failed.");
     }
 
     potential.setScaling(null);
     return potential;
   }
 
   /**
    * {@inheritDoc}
    *
    * <p>Implement the OptimizationListener interface.
    *
    * @since 1.0
    */
   @Override
   public boolean optimizationUpdate(int iteration, int nBFGS, int functionEvaluations,
                                     double rmsGradient, double rmsCoordinateChange, double energy, double energyChange,
                                     double angle, LineSearch.LineSearchResult lineSearchResult) {
     long currentTime = System.nanoTime();
     Double seconds = (currentTime - time) * 1.0e-9;
     time = currentTime;
     this.rmsGradient = rmsGradient;
     this.nSteps = iteration;
     this.energy = energy;
 
     if (iteration == 0) {
       if (nBFGS > 0) {
         logger.info("\n Limited Memory BFGS Quasi-Newton Optimization: \n");
       } else {
         logger.info("\n Steepest Decent Optimization: \n");
       }
       logger.info(" Cycle       Energy      G RMS    Delta E   Delta X    Angle  Evals     Time\n");
     }
     if (lineSearchResult == null) {
       logger.info(format("%6d%13.4f%11.4f", iteration, energy, rmsGradient));
     } else {
       if (lineSearchResult == LineSearch.LineSearchResult.Success) {
         logger.info(
             format("%6d%13.4f%11.4f%11.4f%10.4f%9.2f%7d %8.3f", iteration, energy, rmsGradient,
                 energyChange, rmsCoordinateChange, angle, functionEvaluations, seconds));
       } else {
         logger.info(format("%6d%13.4f%11.4f%11.4f%10.4f%9.2f%7d %8s", iteration, energy, rmsGradient,
             energyChange, rmsCoordinateChange, angle, functionEvaluations, lineSearchResult));
       }
     }
     // Update the listener and check for a termination request.
     if (algorithmListener != null) {
       algorithmListener.algorithmUpdate(molecularAssembly);
     }
 
     if (terminate) {
       logger.info(" The optimization received a termination request.");
       // Tell the L-BFGS optimizer to terminate.
       return false;
     }
     return true;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void terminate() {
     terminate = true;
     while (!done) {
       synchronized (this) {
         try {
           wait(1);
         } catch (Exception e) {
           logger.log(Level.WARNING, "Exception terminating minimization.\n", e);
         }
       }
     }
   }
 
   /**
    * Enumerates available molecular minimization engines; presently limited to the FFX reference
    * engine and the OpenMM engine.
    *
    * <p>Distinct from the force field energy Platform, as the FFX engine can use OpenMM energies,
    * but not vice-versa.
    */
   public enum MinimizationEngine {
     FFX(true, true), OPENMM(false, true);
 
     // Set of supported Platforms. The EnumSet paradigm is very efficient, as it
     // is internally stored as a bit field.
     private final EnumSet<Platform> platforms = EnumSet.noneOf(Platform.class);
 
     /**
      * Constructs a DynamicsEngine using the two presently known types of Platform.
      *
      * @param ffx    Add support for the FFX reference energy platform.
      * @param openMM Add support for the OpenMM energy platforms.
      */
     MinimizationEngine(boolean ffx, boolean openMM) {
       if (ffx) {
         platforms.add(Platform.FFX);
       }
       if (openMM) {
         platforms.add(Platform.OMM);
         platforms.add(Platform.OMM_REF);
         platforms.add(Platform.OMM_CUDA);
         platforms.add(Platform.OMM_OPENCL);
         platforms.add(Platform.OMM_CPU);
       }
     }
 
     /**
      * Gets the set of Platforms supported by this DynamicsEngine
      *
      * @return An EnumSet
      */
     public EnumSet<Platform> getSupportedPlatforms() {
       return EnumSet.copyOf(platforms);
     }
 
     /**
      * Checks if this energy Platform is supported by this DynamicsEngine
      *
      * @param platform The requested platform.
      * @return If supported
      */
     public boolean supportsPlatform(Platform platform) {
       return platforms.contains(platform);
     }
   }
 }