// ******************************************************************************
   //
   // 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.xray.parallel;
  
  import edu.rit.pj.IntegerSchedule;
  import edu.rit.util.Range;
  
  import static java.lang.System.arraycopy;
  import static java.util.Arrays.fill;
  
  /**
   * GradientSchedule class.
   *
   * @author Armin Avdic
   * @since 1.0
   */
  public class GradientSchedule extends IntegerSchedule {
  
    private final int[] lowerBounds;
    private final int nAtoms;
    private int nThreads;
    private boolean[] threadDone;
    private Range[] ranges;
    private int[] weights;
  
    /**
     * Constructor for GradientSchedule.
     *
     * @param nThreads a int.
     * @param nAtoms   a int.
     */
    public GradientSchedule(int nThreads, int nAtoms) {
      this.nThreads = nThreads;
      threadDone = new boolean[nThreads];
      ranges = new Range[nThreads];
      lowerBounds = new int[nThreads + 1];
      this.nAtoms = nAtoms;
    }
  
    /**
     * Getter for the field <code>lowerBounds</code>.
     *
     * @return a copy of the lower bounds array.
     */
    public int[] getLowerBounds() {
      int[] boundsToReturn = new int[nThreads];
      arraycopy(lowerBounds, 1, boundsToReturn, 0, nThreads);
      return boundsToReturn;
    }
  
    /**
     * getThreadWeights.
     *
     * @return a copy of the thread weights array.
     */
    public int[] getThreadWeights() {
      int[] weightsToReturn = new int[nThreads];
      arraycopy(weights, 0, weightsToReturn, 0, nThreads);
      return weightsToReturn;
    }
  
    /**
     * {@inheritDoc}
     */
   @Override
   public boolean isFixedSchedule() {
     return true;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public Range next(int threadID) {
     if (!threadDone[threadID]) {
       threadDone[threadID] = true;
       return ranges[threadID];
     }
     return null;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public void start(int nThreads, Range chunkRange) {
     this.nThreads = nThreads;
 
     if (nThreads != threadDone.length) {
       threadDone = new boolean[nThreads];
     }
     fill(threadDone, false);
 
     if (nThreads != ranges.length) {
       ranges = new Range[nThreads];
     }
     fill(lowerBounds, 0);
     defineRanges();
   }
 
   /**
    * updateWeights.
    *
    * @param weights an array of weights.
    */
   public void updateWeights(int[] weights) {
     this.weights = weights;
   }
 
   private int totalWeight() {
     int totalWeight = 0;
     for (int i = 0; i < nAtoms; i++) {
       totalWeight += weights[i];
     }
     return totalWeight;
   }
 
   private void defineRanges() {
     double totalWeight = totalWeight();
 
     /*
      Infrequent edge case where the total weight is less than or equal to
      the number of threads.
     */
     if (totalWeight <= nThreads) {
       Range temp = new Range(0, nAtoms - 1);
       ranges = temp.subranges(nThreads);
       return;
     }
 
     /*
      Handle the case where we only have a single thread, which will
      receive all the atoms.
     */
     if (nThreads == 1) {
       ranges[0] = new Range(0, nAtoms - 1);
       return;
     }
 
     double targetWeight = (totalWeight / nThreads);
     int lastAtom = nAtoms - 1;
 
     int currentAtom = 0;
     lowerBounds[0] = 0;
     int currentThread = 0;
     while (currentThread < nThreads) {
       int threadWeight = 0;
       while (threadWeight < targetWeight && currentAtom < lastAtom) {
         threadWeight += weights[currentAtom];
         currentAtom++;
       }
       currentThread++;
       if (currentAtom < lastAtom) {
         lowerBounds[currentThread] = currentAtom;
       } else {
         lowerBounds[currentThread] = lastAtom;
         break;
       }
     }
 
     int lastThread = currentThread;
 
     // Loop over all threads that will receive work except the final one.
     for (currentThread = 0; currentThread < lastThread - 1; currentThread++) {
       ranges[currentThread] =
           new Range(lowerBounds[currentThread], lowerBounds[currentThread + 1] - 1);
     }
 
     // Final range for the last thread that will receive work.
     ranges[lastThread - 1] = new Range(lowerBounds[lastThread - 1], lastAtom);
 
     // Left-over threads with null ranges.
     for (int it = lastThread; it < nThreads; it++) {
       ranges[it] = null;
     }
   }
 }