/*
 * Copyright 2007 ZXing authors
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.jwetherell.quick_response_code.qrcode.detector;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;

import com.google.zxing.DecodeHintType;
import com.google.zxing.NotFoundException;
import com.google.zxing.ResultPoint;
import com.google.zxing.ResultPointCallback;
import com.google.zxing.common.BitMatrix;

/**
 * <p>
 * This class attempts to find finder patterns in a QR Code. Finder patterns are
 * the square markers at three corners of a QR Code.
 * </p>
 * 
 * <p>
 * This class is thread-safe but not reentrant. Each thread must allocate its
 * own object.
 * 
 * @author Sean Owen
 */
public class FinderPatternFinder {

    private static final int CENTER_QUORUM = 2;
    protected static final int MIN_SKIP = 3; // 1 pixel/module times 3
                                             // modules/center
    protected static final int MAX_MODULES = 57; // support up to version 10 for
                                                 // mobile clients
    private static final int INTEGER_MATH_SHIFT = 8;

    private final BitMatrix image;
    private final List<FinderPattern> possibleCenters;
    private boolean hasSkipped;
    private final int[] crossCheckStateCount;
    private final ResultPointCallback resultPointCallback;

    /**
     * <p>
     * Creates a finder that will search the image for three finder patterns.
     * </p>
     * 
     * @param image
     *            image to search
     */
    public FinderPatternFinder(BitMatrix image) {
        this(image, null);
    }

    public FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback) {
        this.image = image;
        this.possibleCenters = new ArrayList<FinderPattern>();
        this.crossCheckStateCount = new int[5];
        this.resultPointCallback = resultPointCallback;
    }

    protected BitMatrix getImage() {
        return image;
    }

    protected List<FinderPattern> getPossibleCenters() {
        return possibleCenters;
    }

    FinderPatternInfo find(Map<DecodeHintType, ?> hints) throws NotFoundException {
        boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
        int maxI = image.getHeight();
        int maxJ = image.getWidth();
        // We are looking for black/white/black/white/black modules in
        // 1:1:3:1:1 ratio; this tracks the number of such modules seen so far

        // Let's assume that the maximum version QR Code we support takes up 1/4
        // the height of the
        // image, and then account for the center being 3 modules in size. This
        // gives the smallest
        // number of pixels the center could be, so skip this often. When trying
        // harder, look for
        // all
        // QR versions regardless of how dense they are.
        int iSkip = (3 * maxI) / (4 * MAX_MODULES);
        if (iSkip < MIN_SKIP || tryHarder) {
            iSkip = MIN_SKIP;
        }

        boolean done = false;
        int[] stateCount = new int[5];
        for (int i = iSkip - 1; i < maxI && !done; i += iSkip) {
            // Get a row of black/white values
            stateCount[0] = 0;
            stateCount[1] = 0;
            stateCount[2] = 0;
            stateCount[3] = 0;
            stateCount[4] = 0;
            int currentState = 0;
            for (int j = 0; j < maxJ; j++) {
                if (image.get(j, i)) {
                    // Black pixel
                    if ((currentState & 1) == 1) { // Counting white pixels
                        currentState++;
                    }
                    stateCount[currentState]++;
                } else { // White pixel
                    if ((currentState & 1) == 0) { // Counting black pixels
                        if (currentState == 4) { // A winner?
                            if (foundPatternCross(stateCount)) { // Yes
                                boolean confirmed = handlePossibleCenter(stateCount, i, j);
                                if (confirmed) {
                                    // Start examining every other line.
                                    // Checking each line turned
                                    // out to be too
                                    // expensive and didn't improve performance.
                                    iSkip = 2;
                                    if (hasSkipped) {
                                        done = haveMultiplyConfirmedCenters();
                                    } else {
                                        int rowSkip = findRowSkip();
                                        if (rowSkip > stateCount[2]) {
                                            // Skip rows between row of lower
                                            // confirmed center
                                            // and top of presumed third
                                            // confirmed center
                                            // but back up a bit to get a full
                                            // chance of detecting
                                            // it, entire width of center of
                                            // finder pattern

                                            // Skip by rowSkip, but back off by
                                            // stateCount[2] (size
                                            // of last center
                                            // of pattern we saw) to be
                                            // conservative, and also back
                                            // off by iSkip which
                                            // is about to be re-added
                                            i += rowSkip - stateCount[2] - iSkip;
                                            j = maxJ - 1;
                                        }
                                    }
                                } else {
                                    stateCount[0] = stateCount[2];
                                    stateCount[1] = stateCount[3];
                                    stateCount[2] = stateCount[4];
                                    stateCount[3] = 1;
                                    stateCount[4] = 0;
                                    currentState = 3;
                                    continue;
                                }
                                // Clear state to start looking again
                                currentState = 0;
                                stateCount[0] = 0;
                                stateCount[1] = 0;
                                stateCount[2] = 0;
                                stateCount[3] = 0;
                                stateCount[4] = 0;
                            } else { // No, shift counts back by two
                                stateCount[0] = stateCount[2];
                                stateCount[1] = stateCount[3];
                                stateCount[2] = stateCount[4];
                                stateCount[3] = 1;
                                stateCount[4] = 0;
                                currentState = 3;
                            }
                        } else {
                            stateCount[++currentState]++;
                        }
                    } else { // Counting white pixels
                        stateCount[currentState]++;
                    }
                }
            }
            if (foundPatternCross(stateCount)) {
                boolean confirmed = handlePossibleCenter(stateCount, i, maxJ);
                if (confirmed) {
                    iSkip = stateCount[0];
                    if (hasSkipped) {
                        // Found a third one
                        done = haveMultiplyConfirmedCenters();
                    }
                }
            }
        }

        FinderPattern[] patternInfo = selectBestPatterns();
        ResultPoint.orderBestPatterns(patternInfo);

        return new FinderPatternInfo(patternInfo);
    }

    /**
     * Given a count of black/white/black/white/black pixels just seen and an
     * end position, figures the location of the center of this run.
     */
    private static float centerFromEnd(int[] stateCount, int end) {
        return (end - stateCount[4] - stateCount[3]) - stateCount[2] / 2.0f;
    }

    /**
     * @param stateCount
     *            count of black/white/black/white/black pixels just read
     * @return true iff the proportions of the counts is close enough to the
     *         1/1/3/1/1 ratios used by finder patterns to be considered a match
     */
    protected static boolean foundPatternCross(int[] stateCount) {
        int totalModuleSize = 0;
        for (int i = 0; i < 5; i++) {
            int count = stateCount[i];
            if (count == 0) {
                return false;
            }
            totalModuleSize += count;
        }
        if (totalModuleSize < 7) {
            return false;
        }
        int moduleSize = (totalModuleSize << INTEGER_MATH_SHIFT) / 7;
        int maxVariance = moduleSize / 2;
        // Allow less than 50% variance from 1-1-3-1-1 proportions
        return Math.abs(moduleSize - (stateCount[0] << INTEGER_MATH_SHIFT)) < maxVariance
                && Math.abs(moduleSize - (stateCount[1] << INTEGER_MATH_SHIFT)) < maxVariance
                && Math.abs(3 * moduleSize - (stateCount[2] << INTEGER_MATH_SHIFT)) < 3 * maxVariance
                && Math.abs(moduleSize - (stateCount[3] << INTEGER_MATH_SHIFT)) < maxVariance
                && Math.abs(moduleSize - (stateCount[4] << INTEGER_MATH_SHIFT)) < maxVariance;
    }

    private int[] getCrossCheckStateCount() {
        crossCheckStateCount[0] = 0;
        crossCheckStateCount[1] = 0;
        crossCheckStateCount[2] = 0;
        crossCheckStateCount[3] = 0;
        crossCheckStateCount[4] = 0;
        return crossCheckStateCount;
    }

    /**
     * <p>
     * After a horizontal scan finds a potential finder pattern, this method
     * "cross-checks" by scanning down vertically through the center of the
     * possible finder pattern to see if the same proportion is detected.
     * </p>
     * 
     * @param startI
     *            row where a finder pattern was detected
     * @param centerJ
     *            center of the section that appears to cross a finder pattern
     * @param maxCount
     *            maximum reasonable number of modules that should be observed
     *            in any reading state, based on the results of the horizontal
     *            scan
     * @return vertical center of finder pattern, or {@link Float#NaN} if not
     *         found
     */
    private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal) {
        BitMatrix image = this.image;

        int maxI = image.getHeight();
        int[] stateCount = getCrossCheckStateCount();

        // Start counting up from center
        int i = startI;
        while (i >= 0 && image.get(centerJ, i)) {
            stateCount[2]++;
            i--;
        }
        if (i < 0) {
            return Float.NaN;
        }
        while (i >= 0 && !image.get(centerJ, i) && stateCount[1] <= maxCount) {
            stateCount[1]++;
            i--;
        }
        // If already too many modules in this state or ran off the edge:
        if (i < 0 || stateCount[1] > maxCount) {
            return Float.NaN;
        }
        while (i >= 0 && image.get(centerJ, i) && stateCount[0] <= maxCount) {
            stateCount[0]++;
            i--;
        }
        if (stateCount[0] > maxCount) {
            return Float.NaN;
        }

        // Now also count down from center
        i = startI + 1;
        while (i < maxI && image.get(centerJ, i)) {
            stateCount[2]++;
            i++;
        }
        if (i == maxI) {
            return Float.NaN;
        }
        while (i < maxI && !image.get(centerJ, i) && stateCount[3] < maxCount) {
            stateCount[3]++;
            i++;
        }
        if (i == maxI || stateCount[3] >= maxCount) {
            return Float.NaN;
        }
        while (i < maxI && image.get(centerJ, i) && stateCount[4] < maxCount) {
            stateCount[4]++;
            i++;
        }
        if (stateCount[4] >= maxCount) {
            return Float.NaN;
        }

        // If we found a finder-pattern-like section, but its size is more than
        // 40% different than
        // the original, assume it's a false positive
        int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
        if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal) {
            return Float.NaN;
        }

        return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : Float.NaN;
    }

    /**
     * <p>
     * Like {@link #crossCheckVertical(int, int, int, int)}, and in fact is
     * basically identical, except it reads horizontally instead of vertically.
     * This is used to cross-cross check a vertical cross check and locate the
     * real center of the alignment pattern.
     * </p>
     */
    private float crossCheckHorizontal(int startJ, int centerI, int maxCount, int originalStateCountTotal) {
        BitMatrix image = this.image;

        int maxJ = image.getWidth();
        int[] stateCount = getCrossCheckStateCount();

        int j = startJ;
        while (j >= 0 && image.get(j, centerI)) {
            stateCount[2]++;
            j--;
        }
        if (j < 0) {
            return Float.NaN;
        }
        while (j >= 0 && !image.get(j, centerI) && stateCount[1] <= maxCount) {
            stateCount[1]++;
            j--;
        }
        if (j < 0 || stateCount[1] > maxCount) {
            return Float.NaN;
        }
        while (j >= 0 && image.get(j, centerI) && stateCount[0] <= maxCount) {
            stateCount[0]++;
            j--;
        }
        if (stateCount[0] > maxCount) {
            return Float.NaN;
        }

        j = startJ + 1;
        while (j < maxJ && image.get(j, centerI)) {
            stateCount[2]++;
            j++;
        }
        if (j == maxJ) {
            return Float.NaN;
        }
        while (j < maxJ && !image.get(j, centerI) && stateCount[3] < maxCount) {
            stateCount[3]++;
            j++;
        }
        if (j == maxJ || stateCount[3] >= maxCount) {
            return Float.NaN;
        }
        while (j < maxJ && image.get(j, centerI) && stateCount[4] < maxCount) {
            stateCount[4]++;
            j++;
        }
        if (stateCount[4] >= maxCount) {
            return Float.NaN;
        }

        // If we found a finder-pattern-like section, but its size is
        // significantly different than
        // the original, assume it's a false positive
        int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
        if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) {
            return Float.NaN;
        }

        return foundPatternCross(stateCount) ? centerFromEnd(stateCount, j) : Float.NaN;
    }

    /**
     * <p>
     * This is called when a horizontal scan finds a possible alignment pattern.
     * It will cross check with a vertical scan, and if successful, will, ah,
     * cross-cross-check with another horizontal scan. This is needed primarily
     * to locate the real horizontal center of the pattern in cases of extreme
     * skew.
     * </p>
     * 
     * <p>
     * If that succeeds the finder pattern location is added to a list that
     * tracks the number of times each location has been nearly-matched as a
     * finder pattern. Each additional find is more evidence that the location
     * is in fact a finder pattern center
     * 
     * @param stateCount
     *            reading state module counts from horizontal scan
     * @param i
     *            row where finder pattern may be found
     * @param j
     *            end of possible finder pattern in row
     * @return true if a finder pattern candidate was found this time
     */
    protected boolean handlePossibleCenter(int[] stateCount, int i, int j) {
        int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
        float centerJ = centerFromEnd(stateCount, j);
        float centerI = crossCheckVertical(i, (int) centerJ, stateCount[2], stateCountTotal);
        if (!Float.isNaN(centerI)) {
            // Re-cross check
            centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
            if (!Float.isNaN(centerJ)) {
                float estimatedModuleSize = stateCountTotal / 7.0f;
                boolean found = false;
                for (int index = 0; index < possibleCenters.size(); index++) {
                    FinderPattern center = possibleCenters.get(index);
                    // Look for about the same center and module size:
                    if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
                        possibleCenters.set(index, center.combineEstimate(centerI, centerJ, estimatedModuleSize));
                        found = true;
                        break;
                    }
                }
                if (!found) {
                    FinderPattern point = new FinderPattern(centerJ, centerI, estimatedModuleSize);
                    possibleCenters.add(point);
                    if (resultPointCallback != null) {
                        resultPointCallback.foundPossibleResultPoint(point);
                    }
                }
                return true;
            }
        }
        return false;
    }

    /**
     * @return number of rows we could safely skip during scanning, based on the
     *         first two finder patterns that have been located. In some cases
     *         their position will allow us to infer that the third pattern must
     *         lie below a certain point farther down in the image.
     */
    private int findRowSkip() {
        int max = possibleCenters.size();
        if (max <= 1) {
            return 0;
        }
        FinderPattern firstConfirmedCenter = null;
        for (FinderPattern center : possibleCenters) {
            if (center.getCount() >= CENTER_QUORUM) {
                if (firstConfirmedCenter == null) {
                    firstConfirmedCenter = center;
                } else {
                    // We have two confirmed centers
                    // How far down can we skip before resuming looking for the
                    // next
                    // pattern? In the worst case, only the difference between
                    // the
                    // difference in the x / y coordinates of the two centers.
                    // This is the case where you find top left last.
                    hasSkipped = true;
                    return (int) (Math.abs(firstConfirmedCenter.getX() - center.getX()) - Math.abs(firstConfirmedCenter.getY() - center.getY())) / 2;
                }
            }
        }
        return 0;
    }

    /**
     * @return true iff we have found at least 3 finder patterns that have been
     *         detected at least {@link #CENTER_QUORUM} times each, and, the
     *         estimated module size of the candidates is "pretty similar"
     */
    private boolean haveMultiplyConfirmedCenters() {
        int confirmedCount = 0;
        float totalModuleSize = 0.0f;
        int max = possibleCenters.size();
        for (FinderPattern pattern : possibleCenters) {
            if (pattern.getCount() >= CENTER_QUORUM) {
                confirmedCount++;
                totalModuleSize += pattern.getEstimatedModuleSize();
            }
        }
        if (confirmedCount < 3) {
            return false;
        }
        // OK, we have at least 3 confirmed centers, but, it's possible that one
        // is a
        // "false positive"
        // and that we need to keep looking. We detect this by asking if the
        // estimated module sizes
        // vary too much. We arbitrarily say that when the total deviation from
        // average exceeds
        // 5% of the total module size estimates, it's too much.
        float average = totalModuleSize / max;
        float totalDeviation = 0.0f;
        for (FinderPattern pattern : possibleCenters) {
            totalDeviation += Math.abs(pattern.getEstimatedModuleSize() - average);
        }
        return totalDeviation <= 0.05f * totalModuleSize;
    }

    /**
     * @return the 3 best {@link FinderPattern}s from our list of candidates.
     *         The "best" are those that have been detected at least
     *         {@link #CENTER_QUORUM} times, and whose module size differs from
     *         the average among those patterns the least
     * @throws NotFoundException
     *             if 3 such finder patterns do not exist
     */
    private FinderPattern[] selectBestPatterns() throws NotFoundException {

        int startSize = possibleCenters.size();
        if (startSize < 3) {
            // Couldn't find enough finder patterns
            throw NotFoundException.getNotFoundInstance();
        }

        // Filter outlier possibilities whose module size is too different
        if (startSize > 3) {
            // But we can only afford to do so if we have at least 4
            // possibilities to choose from
            float totalModuleSize = 0.0f;
            float square = 0.0f;
            for (FinderPattern center : possibleCenters) {
                float size = center.getEstimatedModuleSize();
                totalModuleSize += size;
                square += size * size;
            }
            float average = totalModuleSize / startSize;
            float stdDev = (float) Math.sqrt(square / startSize - average * average);

            Collections.sort(possibleCenters, new FurthestFromAverageComparator(average));

            float limit = Math.max(0.2f * average, stdDev);

            for (int i = 0; i < possibleCenters.size() && possibleCenters.size() > 3; i++) {
                FinderPattern pattern = possibleCenters.get(i);
                if (Math.abs(pattern.getEstimatedModuleSize() - average) > limit) {
                    possibleCenters.remove(i);
                    i--;
                }
            }
        }

        if (possibleCenters.size() > 3) {
            // Throw away all but those first size candidate points we found.

            float totalModuleSize = 0.0f;
            for (FinderPattern possibleCenter : possibleCenters) {
                totalModuleSize += possibleCenter.getEstimatedModuleSize();
            }

            float average = totalModuleSize / possibleCenters.size();

            Collections.sort(possibleCenters, new CenterComparator(average));

            possibleCenters.subList(3, possibleCenters.size()).clear();
        }

        return new FinderPattern[] { possibleCenters.get(0), possibleCenters.get(1), possibleCenters.get(2) };
    }

    /**
     * <p>
     * Orders by furthest from average
     * </p>
     */
    private static class FurthestFromAverageComparator implements Comparator<FinderPattern>, Serializable {

        private static final long serialVersionUID = -952816274045567736L;

        private final float average;

        private FurthestFromAverageComparator(float f) {
            average = f;
        }

        @Override
        public int compare(FinderPattern center1, FinderPattern center2) {
            float dA = Math.abs(center2.getEstimatedModuleSize() - average);
            float dB = Math.abs(center1.getEstimatedModuleSize() - average);
            return dA < dB ? -1 : dA == dB ? 0 : 1;
        }
    }

    /**
     * <p>
     * Orders by {@link FinderPattern#getCount()}, descending.
     * </p>
     */
    private static class CenterComparator implements Comparator<FinderPattern>, Serializable {

        private static final long serialVersionUID = 3071314294685511174L;

        private final float average;

        private CenterComparator(float f) {
            average = f;
        }

        @Override
        public int compare(FinderPattern center1, FinderPattern center2) {
            if (center2.getCount() == center1.getCount()) {
                float dA = Math.abs(center2.getEstimatedModuleSize() - average);
                float dB = Math.abs(center1.getEstimatedModuleSize() - average);
                return dA < dB ? 1 : dA == dB ? 0 : -1;
            }
            return center2.getCount() - center1.getCount();
        }
    }
}
