/*
 *                    BioJava development code
 *
 * This code may be freely distributed and modified under the
 * terms of the GNU Lesser General Public Licence.  This should
 * be distributed with the code.  If you do not have a copy,
 * see:
 *
 *      http://www.gnu.org/copyleft/lesser.html
 *
 * Copyright for this code is held jointly by the individual
 * authors.  These should be listed in @author doc comments.
 *
 * For more information on the BioJava project and its aims,
 * or to join the biojava-l mailing list, visit the home page
 * at:
 *
 *      http://www.biojava.org/
 *
 */
package org.biojava.nbio.structure.symmetry.internal;

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

import org.biojava.nbio.structure.Atom;
import org.biojava.nbio.structure.StructureException;
import org.biojava.nbio.structure.align.multiple.Block;
import org.biojava.nbio.structure.align.multiple.MultipleAlignment;
import org.biojava.nbio.structure.align.multiple.MultipleAlignmentEnsemble;
import org.biojava.nbio.structure.align.multiple.util.MultipleAlignmentScorer;
import org.biojava.nbio.structure.align.multiple.util.MultipleAlignmentTools;
import org.biojava.nbio.structure.jama.Matrix;
import org.biojava.nbio.structure.symmetry.utils.SymmetryTools;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Optimizes a symmetry alignment by a Monte Carlo score optimization of the
 * repeat multiple alignment. The superposition of the repeats is not free
 * (felxible), because it is constrained on the symmetry axes found in the
 * structure. This is the main difference to the {@link org.biojava.nbio.structure.align.multiple.mc.MultipleMcMain} algorithm in
 * biojava. Another major difference is that the free Pool is shared for all
 * repeats, so that no residue can appear to more than one repeat at a time.
 * <p>
 * This algorithm does not use a unfiform distribution for selecting moves,
 * farther residues have more probability to be shrinked or gapped. This
 * modification of the algorithm improves convergence and running time.
 * <p>
 * Use call method to parallelize optimizations, or use optimize method instead.
 * Because gaps are allowed in the repeats, a {@link MultipleAlignment} format
 * is returned.
 *
 * @author Aleix Lafita
 * @since 4.1.1
 *
 */
public class SymmOptimizer {

        private static final Logger logger = LoggerFactory
                        .getLogger(SymmOptimizer.class);

        private Random rnd;

        // Optimization parameters
        private int Rmin = 2; // min aligned repeats per column
        private int Lmin; // min repeat length
        private int maxIter; // max iterations
        private double C = 20; // probability of accept bad moves constant

        // Score function parameters
        private static final double Gopen = 20.0; // Penalty for opening gap
        private static final double Gextend = 10.0; // Penalty for extending gaps
        private double dCutoff;

        // Alignment Information
        private MultipleAlignment msa;
        private SymmetryAxes axes;
        private Atom[] atoms;
        private int order;
        private int length; // total alignment columns (block size)
        private int repeatCore; // core length (without gaps)

        // Aligned Residues and Score
        private List<List<Integer>> block; // residues aligned
        private List<Integer> freePool; // residues not aligned
        private double mcScore; // alignment score to optimize

        // Variables that store the history of the optimization - slower if on
        private static final boolean history = false;
        private static final int saveStep = 100;
        private static final String pathToHistory = "results/symm-opt/";
        private List<Long> timeHistory;
        private List<Integer> lengthHistory;
        private List<Double> rmsdHistory;
        private List<Double> tmScoreHistory;
        private List<Double> mcScoreHistory;

        /**
         * Constructor with a seed MultipleAlignment storing a refined symmetry
         * alignment of the repeats. To perform the optimization use the call or
         * optimize methods after instantiation.
         *
         * @param symmResult
         *            CeSymmResult with all the information
         */
        public SymmOptimizer(CeSymmResult symmResult) {

                this.axes = symmResult.getAxes();
                this.rnd = new Random(symmResult.getParams().getRndSeed());
                this.Lmin = symmResult.getParams().getMinCoreLength();
                this.dCutoff = symmResult.getParams().getDistanceCutoff();

                MultipleAlignmentEnsemble e = symmResult.getMultipleAlignment()
                                .getEnsemble().clone();
                this.msa = e.getMultipleAlignment(0);

                this.atoms = msa.getAtomArrays().get(0);
                this.order = msa.size();
                this.repeatCore = msa.getCoreLength();

                // 50% of the structures aligned (minimum) or all (no gaps)
                if (symmResult.getParams().isGaps())
                        Rmin = Math.max(order / 2, 2);
                else
                        Rmin = order;

                maxIter = symmResult.getParams().getOptimizationSteps();
                if (maxIter < 1)
                        maxIter = 100 * atoms.length;
        }

        private void initialize() throws StructureException, RefinerFailedException {

                if (order == 1)
                        throw new RefinerFailedException(
                                        "Non-symmetric seed alignment: order = 1");
                if (repeatCore < 1)
                        throw new RefinerFailedException(
                                        "Seed alignment too short: repeat core length < 1");

                // Initialize the history variables
                timeHistory = new ArrayList<>();
                lengthHistory = new ArrayList<>();
                rmsdHistory = new ArrayList<>();
                mcScoreHistory = new ArrayList<>();
                tmScoreHistory = new ArrayList<>();

                C = 20 * order;

                // Initialize alignment variables
                block = msa.getBlock(0).getAlignRes();
                freePool = new ArrayList<>();
                length = block.get(0).size();

                // Store the residues aligned in the block
                List<Integer> aligned = new ArrayList<>();
                for (int su = 0; su < order; su++)
                        aligned.addAll(block.get(su));

                // Add any residue not aligned to the free pool
                for (int i = 0; i < atoms.length; i++) {
                        if (!aligned.contains(i))
                                freePool.add(i);
                }
                checkGaps();

                // Set the MC score of the initial state (seed alignment)
                updateMultipleAlignment();
                mcScore = MultipleAlignmentScorer.getMCScore(msa, Gopen, Gextend,
                                dCutoff);
        }

        /**
         * Optimization method based in a Monte-Carlo approach. Starting from the
         * refined alignment uses 4 types of moves:
         * <p>
         * <ul>
         * <li>1- Shift Row: if there are enough freePool residues available.
         * <li>2- Expand Block: add another alignment column.
         * <li>3- Shrink Block: move a block column to the freePool.
         * <li>4- Insert gap: insert a gap in a position of the alignment.
         * </ul>
         * @throws StructureException
         * @throws RefinerFailedException
         *             if the alignment is not symmetric or too short.
         */
        public MultipleAlignment optimize() throws StructureException,
                        RefinerFailedException {

                initialize();

                // Save the optimal alignment
                List<List<Integer>> optBlock = new ArrayList<>();
                List<Integer> optFreePool = new ArrayList<>();
                optFreePool.addAll(freePool);
                for (int k = 0; k < order; k++) {
                        List<Integer> b = new ArrayList<>();
                        b.addAll(block.get(k));
                        optBlock.add(b);
                }
                double optScore = mcScore;

                int conv = 0; // Number of steps without an alignment improvement
                int i = 1;
                int stepsToConverge = Math.max(maxIter / 50, 1000);
                long initialTime = System.nanoTime()/1000000;

                while (i < maxIter && conv < stepsToConverge) {

                        // Save the state of the system
                        List<List<Integer>> lastBlock = new ArrayList<>();
                        List<Integer> lastFreePool = new ArrayList<>();
                        lastFreePool.addAll(freePool);
                        for (int k = 0; k < order; k++) {
                                List<Integer> b = new ArrayList<>();
                                b.addAll(block.get(k));
                                lastBlock.add(b);
                        }
                        double lastScore = mcScore;
                        int lastRepeatCore = repeatCore;

                        boolean moved = false;

                        while (!moved) {
                                // Randomly select one of the steps to modify the alignment.
                                // Because of biased moves, the probabilities are not the same
                                double move = rnd.nextDouble();
                                if (move < 0.4) {
                                        moved = shiftRow();
                                        logger.debug("did shift");
                                } else if (move < 0.7) {
                                        moved = expandBlock();
                                        logger.debug("did expand");
                                } else if (move < 0.85) {
                                        moved = shrinkBlock();
                                        logger.debug("did shrink");
                                } else {
                                        moved = insertGap();
                                        logger.debug("did insert gap");
                                }
                        }

                        // Get the properties of the new alignment
                        updateMultipleAlignment();
                        mcScore = MultipleAlignmentScorer.getMCScore(msa, Gopen, Gextend,
                                        dCutoff);

                        // Calculate change in the optimization Score
                        double AS = mcScore - lastScore;
                        double prob = 1.0;

                        if (AS < 0) {

                                // Probability of accepting bad move
                                prob = probabilityFunction(AS, i, maxIter);
                                double p = rnd.nextDouble();

                                // Reject the move
                                if (p > prob) {
                                        block = lastBlock;
                                        freePool = lastFreePool;
                                        length = block.get(0).size();
                                        repeatCore = lastRepeatCore;
                                        mcScore = lastScore;
                                        conv++; // no change in score if rejected

                                } else
                                        conv = 0; // if accepted

                        } else
                                conv = 0; // if positive change

                        logger.debug(i + ": --prob: " + prob + ", --score: " + AS
                                        + ", --conv: " + conv);

                        // Store as the optimal alignment if better
                        if (mcScore > optScore) {
                                optBlock = new ArrayList<>();
                                optFreePool = new ArrayList<>();
                                optFreePool.addAll(freePool);
                                for (int k = 0; k < order; k++) {
                                        List<Integer> b = new ArrayList<>();
                                        b.addAll(block.get(k));
                                        optBlock.add(b);
                                }
                                optScore = mcScore;
                        }

                        if (history) {
                                if (i % saveStep == 1) {
                                        // Get the correct superposition again
                                        updateMultipleAlignment();

                                        timeHistory.add(System.nanoTime()/1000000 - initialTime);
                                        lengthHistory.add(length);
                                        rmsdHistory.add(msa.getScore(MultipleAlignmentScorer.RMSD));
                                        tmScoreHistory.add(msa
                                                        .getScore(MultipleAlignmentScorer.AVGTM_SCORE));
                                        mcScoreHistory.add(mcScore);
                                }
                        }

                        i++;
                }

                // Use the optimal alignment of the trajectory
                block = optBlock;
                freePool = optFreePool;
                mcScore = optScore;

                // Superimpose and calculate final scores
                updateMultipleAlignment();
                msa.putScore(MultipleAlignmentScorer.MC_SCORE, mcScore);

                // Save the history to the results folder of the symmetry project
                if (history) {
                        try {
                                saveHistory(pathToHistory);
                        } catch (Exception e) {
                                logger.warn("Could not save history file: " + e.getMessage());
                        }
                }

                return msa;
        }

        /**
         * This method translates the internal data structures to a
         * MultipleAlignment of the repeats in order to use the methods to score
         * MultipleAlignments.
         *
         * @throws StructureException
         * @throws RefinerFailedException
         */
        private void updateMultipleAlignment() throws StructureException,
                        RefinerFailedException {

                msa.clear();

                // Override the alignment with the new information
                Block b = msa.getBlock(0);
                b.setAlignRes(block);
                repeatCore = b.getCoreLength();
                if (repeatCore < 1)
                        throw new RefinerFailedException(
                                        "Optimization converged to length 0");

                SymmetryTools.updateSymmetryTransformation(axes, msa);
        }

        /**
         * Method that loops through all the alignment columns and checks that there
         * are no more gaps than the maximum allowed: Rmin.
         * <p>
         * There must be at least Rmin residues different than null in every
         * alignment column. In case there is a column with more gaps than allowed
         * it will be shrinked (moved to freePool).
         *
         * @return true if any columns has been shrinked and false otherwise
         */
        private boolean checkGaps() {

                List<Integer> shrinkColumns = new ArrayList<>();
                // Loop for each column
                for (int res = 0; res < length; res++) {
                        int gapCount = 0;
                        // Loop for each repeat and count the gaps
                        for (int su = 0; su < order; su++) {
                                if (block.get(su).get(res) == null)
                                        gapCount++;
                        }
                        if ((order - gapCount) < Rmin) {
                                // Add the column to the shrink list
                                shrinkColumns.add(res);
                        }
                }

                // Shrink the columns that have more gaps than allowed
                for (int col = shrinkColumns.size() - 1; col >= 0; col--) {
                        for (int su = 0; su < order; su++) {
                                Integer residue = block.get(su).get(shrinkColumns.get(col));
                                block.get(su).remove((int) shrinkColumns.get(col));
                                if (residue != null)
                                        freePool.add(residue);
                                Collections.sort(freePool);
                        }
                        length--;
                }

                if (shrinkColumns.size() != 0)
                        return true;
                else
                        return false;
        }

        /**
         * Insert a gap in one of the repeats into selected position (by higher
         * distances) in the alignment. Calculates the average residue distance to
         * make the choice. A gap is a null in the block.
         *
         * @throws StructureException
         * @throws RefinerFailedException
         */
        private boolean insertGap() throws StructureException,
                        RefinerFailedException {

                // Let gaps only if the repeat is larger than the minimum length
                if (repeatCore <= Lmin)
                        return false;

                // Select residue by maximum distance
                updateMultipleAlignment();
                Matrix residueDistances = MultipleAlignmentTools
                                .getAverageResidueDistances(msa);

                double maxDist = Double.MIN_VALUE;
                int su = 0;
                int res = 0;
                for (int col = 0; col < length; col++) {
                        for (int s = 0; s < order; s++) {
                                if (residueDistances.get(s, col) != -1) {
                                        if (residueDistances.get(s, col) > maxDist) {
                                                // geometric distribution
                                                if (rnd.nextDouble() > 0.5) {
                                                        su = s;
                                                        res = col;
                                                        maxDist = residueDistances.get(s, col);
                                                }
                                        }
                                }
                        }
                }

                // Insert the gap at the position
                Integer residueL = block.get(su).get(res);
                if (residueL != null) {
                        freePool.add(residueL);
                        Collections.sort(freePool);
                } else
                        return false; // If there was a gap already in the position.

                block.get(su).set(res, null);
                checkGaps();
                return true;
        }

        /**
         * Move all the block residues of one repeat one position to the left or
         * right and move the corresponding boundary residues from the freePool to
         * the block, and viceversa.
         * <p>
         * The boundaries are determined by any irregularity (either a gap or a
         * discontinuity in the alignment.
         */
        private boolean shiftRow() {

                int su = rnd.nextInt(order); // Select the repeat
                int rl = rnd.nextInt(2); // Select between moving right (0) or left (1)
                int res = rnd.nextInt(length); // Residue as a pivot

                // When the pivot residue is null try to add a residue from the freePool
                if (block.get(su).get(res) == null) {

                        int right = res;
                        int left = res;
                        // Find the boundary to the right abd left
                        while (block.get(su).get(right) == null && right < length - 1) {
                                right++;
                        }
                        while (block.get(su).get(left) == null && left > 0) {
                                left--;
                        }

                        // If they both are null the whole block is null
                        if (block.get(su).get(left) == null
                                        && block.get(su).get(right) == null) {
                                return false;
                        } else if (block.get(su).get(left) == null) {
                                // Choose the sequentially previous residue of the known one
                                Integer residue = block.get(su).get(right) - 1;
                                if (freePool.contains(residue)) {
                                        block.get(su).set(res, residue);
                                        freePool.remove(residue);
                                } else
                                        return false;
                        } else if (block.get(su).get(right) == null) {
                                // Choose the sequentially next residue of the known one
                                Integer residue = block.get(su).get(left) + 1;
                                if (freePool.contains(residue)) {
                                        block.get(su).set(res, residue);
                                        freePool.remove(residue);
                                } else
                                        return false;
                        } else {
                                // If boundaries are consecutive swap null and position (R or L)
                                if (block.get(su).get(right) == block.get(su).get(left) + 1) {
                                        switch (rl) {
                                        case 0: // to the right
                                                block.get(su).set(right - 1, block.get(su).get(right));
                                                block.get(su).set(right, null);
                                                break;
                                        case 1: // to the left
                                                block.get(su).set(left + 1, block.get(su).get(left));
                                                block.get(su).set(left, null);
                                                break;
                                        }
                                } else {
                                        // Choose randomly a residue in between left and right to
                                        // add
                                        Integer residue = rnd.nextInt(block.get(su).get(right)
                                                        - block.get(su).get(left) - 1)
                                                        + block.get(su).get(left) + 1;

                                        if (freePool.contains(residue)) {
                                                block.get(su).set(res, residue);
                                                freePool.remove(residue);
                                        }
                                }
                        }
                        return true;
                }

                // When the residue is different than null
                switch (rl) {
                case 0: // Move to the right

                        int leftBoundary = res - 1;
                        int leftPrevRes = res;
                        while (true) {
                                if (leftBoundary < 0)
                                        break;
                                else {
                                        if (block.get(su).get(leftBoundary) == null) {
                                                break; // gap
                                        } else if (block.get(su).get(leftPrevRes) > block.get(su)
                                                        .get(leftBoundary) + 1) {
                                                break; // discontinuity
                                        }
                                }
                                leftPrevRes = leftBoundary;
                                leftBoundary--;
                        }
                        leftBoundary++;

                        int rightBoundary = res + 1;
                        int rightPrevRes = res;
                        while (true) {
                                if (rightBoundary == length)
                                        break;
                                else {
                                        if (block.get(su).get(rightBoundary) == null) {
                                                break; // gap
                                        } else if (block.get(su).get(rightPrevRes) + 1 < block.get(
                                                        su).get(rightBoundary)) {
                                                break; // discontinuity
                                        }
                                }
                                rightPrevRes = rightBoundary;
                                rightBoundary++;
                        }
                        rightBoundary--;

                        // Residues at the boundary
                        Integer residueR0 = block.get(su).get(rightBoundary);
                        Integer residueL0 = block.get(su).get(leftBoundary);

                        // Remove residue at the right of the block and add to the freePool
                        block.get(su).remove(rightBoundary);
                        if (residueR0 != null) {
                                freePool.add(residueR0);
                                Collections.sort(freePool);
                        }

                        // Add the residue at the left of the block
                        residueL0 -= 1; // cannot be null, throw exception if it is
                        if (freePool.contains(residueL0)) {
                                block.get(su).add(leftBoundary, residueL0);
                                freePool.remove(residueL0);
                        } else {
                                block.get(su).add(leftBoundary, null);
                        }
                        break;

                case 1: // Move to the left

                        int leftBoundary1 = res - 1;
                        int leftPrevRes1 = res;
                        while (true) {
                                if (leftBoundary1 < 0)
                                        break;
                                else {
                                        if (block.get(su).get(leftBoundary1) == null) {
                                                break; // gap
                                        } else if (block.get(su).get(leftPrevRes1) > block.get(su)
                                                        .get(leftBoundary1) + 1) {
                                                break; // discontinuity
                                        }
                                }
                                leftPrevRes1 = leftBoundary1;
                                leftBoundary1--;
                        }
                        leftBoundary1++;

                        int rightBoundary1 = res + 1;
                        int rightPrevRes1 = res;
                        while (true) {
                                if (rightBoundary1 == length)
                                        break;
                                else {
                                        if (block.get(su).get(rightBoundary1) == null) {
                                                break; // gap
                                        } else if (block.get(su).get(rightPrevRes1) + 1 < block
                                                        .get(su).get(rightBoundary1)) {
                                                break; // discontinuity
                                        }
                                }
                                rightPrevRes1 = rightBoundary1;
                                rightBoundary1++;
                        }
                        rightBoundary1--;

                        // Residues at the boundary
                        Integer residueR1 = block.get(su).get(rightBoundary1);
                        Integer residueL1 = block.get(su).get(leftBoundary1);

                        // Add the residue at the right of the block
                        residueR1 += 1; // cannot be null
                        if (freePool.contains(residueR1)) {
                                if (rightBoundary1 == length - 1)
                                        block.get(su).add(residueR1);
                                else
                                        block.get(su).add(rightBoundary1 + 1, residueR1);
                                freePool.remove(residueR1);
                        } else {
                                block.get(su).add(rightBoundary1 + 1, null);
                        }

                        // Remove the residue at the left of the block
                        block.get(su).remove(leftBoundary1);
                        freePool.add(residueL1);
                        Collections.sort(freePool);
                        break;
                }
                checkGaps();
                return true;
        }

        /**
         * It extends the alignment one position to the right or to the left of a
         * randomly selected position by moving the consecutive residues of each
         * repeat (if present) from the freePool to the block.
         * <p>
         * If there are not enough residues in the freePool it introduces gaps.
         */
        private boolean expandBlock() {

                boolean moved = false;

                int rl = rnd.nextInt(2); // Select between right (0) or left (1)
                int res = rnd.nextInt(length); // Residue as a pivot

                switch (rl) {
                case 0:

                        int rightBoundary = res;
                        int[] previousPos = new int[order];
                        for (int su = 0; su < order; su++)
                                previousPos[su] = -1;

                        // Search a position to the right that has at minimum Rmin
                        while (length - 1 > rightBoundary) {
                                int noncontinuous = 0;
                                for (int su = 0; su < order; su++) {
                                        if (block.get(su).get(rightBoundary) == null) {
                                                continue;
                                        } else if (previousPos[su] == -1) {
                                                previousPos[su] = block.get(su).get(rightBoundary);
                                        } else if (block.get(su).get(rightBoundary) > previousPos[su] + 1) {
                                                noncontinuous++;
                                        }
                                }
                                if (noncontinuous < Rmin)
                                        rightBoundary++;
                                else
                                        break;
                        }
                        if (rightBoundary > 0)
                                rightBoundary--;

                        // Expand the block with the residues at the repeat boundaries
                        for (int su = 0; su < order; su++) {
                                Integer residueR = block.get(su).get(rightBoundary);
                                if (residueR == null) {
                                        if (rightBoundary == length - 1)
                                                block.get(su).add(null);
                                        else
                                                block.get(su).add(rightBoundary + 1, null);
                                } else if (freePool.contains(residueR + 1)) {
                                        Integer residueAdd = residueR + 1;
                                        if (rightBoundary == length - 1) {
                                                block.get(su).add(residueAdd);
                                        } else
                                                block.get(su).add(rightBoundary + 1, residueAdd);
                                        freePool.remove(residueAdd);
                                } else {
                                        if (rightBoundary == length - 1)
                                                block.get(su).add(null);
                                        else
                                                block.get(su).add(rightBoundary + 1, null);
                                }
                        }
                        length++;
                        moved = true;
                        break;

                case 1:

                        int leftBoundary = res;
                        int[] nextPos = new int[order];
                        for (int su = 0; su < order; su++)
                                nextPos[su] = -1;

                        // Search a position to the right that has at minimum Rmin
                        while (leftBoundary > 0) {
                                int noncontinuous = 0;
                                for (int su = 0; su < order; su++) {
                                        if (block.get(su).get(leftBoundary) == null) {
                                                continue;
                                        } else if (nextPos[su] == -1) {
                                                nextPos[su] = block.get(su).get(leftBoundary);
                                        } else if (block.get(su).get(leftBoundary) < nextPos[su] - 1) {
                                                noncontinuous++;
                                        }
                                }
                                if (noncontinuous < Rmin)
                                        leftBoundary--;
                                else
                                        break;
                        }

                        // Expand the block with the residues at the repeat boundaries
                        for (int su = 0; su < order; su++) {
                                Integer residueL = block.get(su).get(leftBoundary);
                                if (residueL == null) {
                                        block.get(su).add(leftBoundary, null);
                                } else if (freePool.contains(residueL - 1)) {
                                        Integer residueAdd = residueL - 1;
                                        block.get(su).add(leftBoundary, residueAdd);
                                        freePool.remove(residueAdd);
                                } else {
                                        block.get(su).add(leftBoundary, null);
                                }
                        }
                        length++;
                        moved = true;
                        break;
                }
                if (moved)
                        return !checkGaps();
                return moved;
        }

        /**
         * Deletes an alignment column at a randomly selected position.
         *
         * @throws StructureException
         * @throws RefinerFailedException
         */
        private boolean shrinkBlock() throws StructureException,
                        RefinerFailedException {

                // Let shrink moves only if the repeat is larger enough
                if (repeatCore <= Lmin)
                        return false;

                // Select column by maximum distance
                updateMultipleAlignment();
                Matrix residueDistances = MultipleAlignmentTools
                                .getAverageResidueDistances(msa);

                double maxDist = Double.MIN_VALUE;
                double[] colDistances = new double[length];
                int res = 0;
                for (int col = 0; col < length; col++) {
                        int normalize = 0;
                        for (int s = 0; s < order; s++) {
                                if (residueDistances.get(s, col) != -1) {
                                        colDistances[col] += residueDistances.get(s, col);
                                        normalize++;
                                }
                        }
                        colDistances[col] /= normalize;
                        if (colDistances[col] > maxDist) {
                                // geometric distribution
                                if (rnd.nextDouble() > 0.5) {
                                        maxDist = colDistances[col];
                                        res = col;
                                }
                        }
                }

                for (int su = 0; su < order; su++) {
                        Integer residue = block.get(su).get(res);
                        block.get(su).remove(res);
                        if (residue != null)
                                freePool.add(residue);
                        Collections.sort(freePool);
                }
                length--;
                checkGaps();
                return true;
        }

        /**
         * Calculates the probability of accepting a bad move given the iteration
         * step and the score change.
         * <p>
         * Function: p=(C-AS)/(C*sqrt(step)) Added a normalization factor so that
         * the probability approaches 0 when the maxIter is reached.
         */
        private double probabilityFunction(double AS, int m, int maxIter) {

                double prob = (C + AS) / (C * Math.sqrt(m));
                double norm = (1 - (m * 1.0) / maxIter); // Normalization factor
                return Math.min(Math.max(prob * norm, 0.0), 1.0);
        }

        /**
         * Save the evolution of the optimization process as a csv file.
         */
        private void saveHistory(String folder) throws IOException {

                String name = msa.getStructureIdentifier(0).getIdentifier();
                FileWriter writer = new FileWriter(folder + name
                                + "-symm_opt.csv");
                writer.append("Step,Time,RepeatLength,RMSD,TMscore,MCscore\n");

                for (int i = 0; i < lengthHistory.size(); i++) {
                        writer.append(i * saveStep + ",");
                        writer.append(timeHistory.get(i) + ",");
                        writer.append(lengthHistory.get(i) + ",");
                        writer.append(rmsdHistory.get(i) + ",");
                        writer.append(tmScoreHistory.get(i) + ",");
                        writer.append(mcScoreHistory.get(i) + "\n");
                }

                writer.flush();
                writer.close();
        }

}