/*
 * 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.util.ArrayList;
import java.util.List;

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

/**
 * <p>
 * This class attempts to find alignment patterns in a QR Code. Alignment
 * patterns look like finder patterns but are smaller and appear at regular
 * intervals throughout the image.
 * </p>
 * 
 * <p>
 * At the moment this only looks for the bottom-right alignment pattern.
 * </p>
 * 
 * <p>
 * This is mostly a simplified copy of {@link FinderPatternFinder}. It is
 * copied, pasted and stripped down here for maximum performance but does
 * unfortunately duplicate some code.
 * </p>
 * 
 * <p>
 * This class is thread-safe but not reentrant. Each thread must allocate its
 * own object.
 * </p>
 * 
 * @author Sean Owen
 */
final class AlignmentPatternFinder {

    private final BitMatrix image;
    private final List<AlignmentPattern> possibleCenters;
    private final int startX;
    private final int startY;
    private final int width;
    private final int height;
    private final float moduleSize;
    private final int[] crossCheckStateCount;
    private final ResultPointCallback resultPointCallback;

    /**
     * <p>
     * Creates a finder that will look in a portion of the whole image.
     * </p>
     * 
     * @param image
     *            image to search
     * @param startX
     *            left column from which to start searching
     * @param startY
     *            top row from which to start searching
     * @param width
     *            width of region to search
     * @param height
     *            height of region to search
     * @param moduleSize
     *            estimated module size so far
     */
    AlignmentPatternFinder(BitMatrix image, int startX, int startY, int width, int height, float moduleSize, ResultPointCallback resultPointCallback) {
        this.image = image;
        this.possibleCenters = new ArrayList<AlignmentPattern>(5);
        this.startX = startX;
        this.startY = startY;
        this.width = width;
        this.height = height;
        this.moduleSize = moduleSize;
        this.crossCheckStateCount = new int[3];
        this.resultPointCallback = resultPointCallback;
    }

    /**
     * <p>
     * This method attempts to find the bottom-right alignment pattern in the
     * image. It is a bit messy since it's pretty performance-critical and so is
     * written to be fast foremost.
     * </p>
     * 
     * @return {@link AlignmentPattern} if found
     * @throws NotFoundException
     *             if not found
     */
    AlignmentPattern find() throws NotFoundException {
        int startX = this.startX;
        int height = this.height;
        int maxJ = startX + width;
        int middleI = startY + (height >> 1);
        // We are looking for black/white/black modules in 1:1:1 ratio;
        // this tracks the number of black/white/black modules seen so far
        int[] stateCount = new int[3];
        for (int iGen = 0; iGen < height; iGen++) {
            // Search from middle outwards
            int i = middleI + ((iGen & 0x01) == 0 ? (iGen + 1) >> 1 : -((iGen + 1) >> 1));
            stateCount[0] = 0;
            stateCount[1] = 0;
            stateCount[2] = 0;
            int j = startX;
            // Burn off leading white pixels before anything else; if we start
            // in the middle of
            // a white run, it doesn't make sense to count its length, since we
            // don't know if the
            // white run continued to the left of the start point
            while (j < maxJ && !image.get(j, i)) {
                j++;
            }
            int currentState = 0;
            while (j < maxJ) {
                if (image.get(j, i)) {
                    // Black pixel
                    if (currentState == 1) { // Counting black pixels
                        stateCount[currentState]++;
                    } else { // Counting white pixels
                        if (currentState == 2) { // A winner?
                            if (foundPatternCross(stateCount)) { // Yes
                                AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, j);
                                if (confirmed != null) {
                                    return confirmed;
                                }
                            }
                            stateCount[0] = stateCount[2];
                            stateCount[1] = 1;
                            stateCount[2] = 0;
                            currentState = 1;
                        } else {
                            stateCount[++currentState]++;
                        }
                    }
                } else { // White pixel
                    if (currentState == 1) { // Counting black pixels
                        currentState++;
                    }
                    stateCount[currentState]++;
                }
                j++;
            }
            if (foundPatternCross(stateCount)) {
                AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, maxJ);
                if (confirmed != null) {
                    return confirmed;
                }
            }

        }

        // Hmm, nothing we saw was observed and confirmed twice. If we had
        // any guess at all, return it.
        if (!possibleCenters.isEmpty()) {
            return possibleCenters.get(0);
        }

        throw NotFoundException.getNotFoundInstance();
    }

    /**
     * Given a count of black/white/black pixels just seen and an end position,
     * figures the location of the center of this black/white/black run.
     */
    private static float centerFromEnd(int[] stateCount, int end) {
        return (end - stateCount[2]) - stateCount[1] / 2.0f;
    }

    /**
     * @param stateCount
     *            count of black/white/black pixels just read
     * @return true iff the proportions of the counts is close enough to the
     *         1/1/1 ratios used by alignment patterns to be considered a match
     */
    private boolean foundPatternCross(int[] stateCount) {
        float moduleSize = this.moduleSize;
        float maxVariance = moduleSize / 2.0f;
        for (int i = 0; i < 3; i++) {
            if (Math.abs(moduleSize - stateCount[i]) >= maxVariance) {
                return false;
            }
        }
        return true;
    }

    /**
     * <p>
     * After a horizontal scan finds a potential alignment pattern, this method
     * "cross-checks" by scanning down vertically through the center of the
     * possible alignment pattern to see if the same proportion is detected.
     * </p>
     * 
     * @param startI
     *            row where an alignment pattern was detected
     * @param centerJ
     *            center of the section that appears to cross an alignment
     *            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 alignment 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 = crossCheckStateCount;
        stateCount[0] = 0;
        stateCount[1] = 0;
        stateCount[2] = 0;

        // Start counting up from center
        int i = startI;
        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[1] <= maxCount) {
            stateCount[1]++;
            i++;
        }
        if (i == maxI || stateCount[1] > maxCount) {
            return Float.NaN;
        }
        while (i < maxI && !image.get(centerJ, i) && stateCount[2] <= maxCount) {
            stateCount[2]++;
            i++;
        }
        if (stateCount[2] > maxCount) {
            return Float.NaN;
        }

        int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
        if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal) {
            return Float.NaN;
        }

        return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : 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 see if
     * this pattern had been found on a previous horizontal scan. If so, we
     * consider it confirmed and conclude we have found the alignment pattern.
     * </p>
     * 
     * @param stateCount
     *            reading state module counts from horizontal scan
     * @param i
     *            row where alignment pattern may be found
     * @param j
     *            end of possible alignment pattern in row
     * @return {@link AlignmentPattern} if we have found the same pattern twice,
     *         or null if not
     */
    private AlignmentPattern handlePossibleCenter(int[] stateCount, int i, int j) {
        int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
        float centerJ = centerFromEnd(stateCount, j);
        float centerI = crossCheckVertical(i, (int) centerJ, 2 * stateCount[1], stateCountTotal);
        if (!Float.isNaN(centerI)) {
            float estimatedModuleSize = (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;
            for (AlignmentPattern center : possibleCenters) {
                // Look for about the same center and module size:
                if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
                    return center.combineEstimate(centerI, centerJ, estimatedModuleSize);
                }
            }
            // Hadn't found this before; save it
            AlignmentPattern point = new AlignmentPattern(centerJ, centerI, estimatedModuleSize);
            possibleCenters.add(point);
            if (resultPointCallback != null) {
                resultPointCallback.foundPossibleResultPoint(point);
            }
        }
        return null;
    }

}
