text: /*
   * 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.google.zxing.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 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<>();
      this.crossCheckStateCount = new int[5];
      this.resultPointCallback = resultPointCallback;
    }
  
    protected final BitMatrix getImage() {
      return image;
    }
  
    protected final List<FinderPattern> getPossibleCenters() {
      return possibleCenters;
    }
  
    final FinderPatternInfo find(Map<DecodeHintType,?> hints) throws NotFoundException {
      boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
      boolean pureBarcode = hints != null && hints.containsKey(DecodeHintType.PURE_BARCODE);
      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, pureBarcode);
                  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, pureBarcode);
          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 (float) (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;
      }
      float moduleSize = totalModuleSize / 7.0f;
      float maxVariance = moduleSize / 2.0f;
      // Allow less than 50% variance from 1-1-3-1-1 proportions
      return
          Math.abs(moduleSize - stateCount[0]) < maxVariance &&
          Math.abs(moduleSize - stateCount[1]) < maxVariance &&
          Math.abs(3.0f * moduleSize - stateCount[2]) < 3 * maxVariance &&
          Math.abs(moduleSize - stateCount[3]) < maxVariance &&
          Math.abs(moduleSize - stateCount[4]) < maxVariance;
    }
  
    private int[] getCrossCheckStateCount() {
      crossCheckStateCount[0] = 0;
      crossCheckStateCount[1] = 0;
      crossCheckStateCount[2] = 0;
      crossCheckStateCount[3] = 0;
      crossCheckStateCount[4] = 0;
      return crossCheckStateCount;
    }
  
    /**
     * After a vertical and horizontal scan finds a potential finder pattern, this method
     * "cross-cross-cross-checks" by scanning down diagonally through the center of the possible
     * finder pattern to see if the same proportion is detected.
     * 
     * @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
     * @param originalStateCountTotal The original state count total.
     * @return true if proportions are withing expected limits
     */
    private boolean crossCheckDiagonal(int startI, int centerJ, int maxCount, int originalStateCountTotal) {
      int[] stateCount = getCrossCheckStateCount();
  
      // Start counting up, left from center finding black center mass
      int i = 0;
      while (startI >= i && centerJ >= i && image.get(centerJ - i, startI - i)) {
        stateCount[2]++;
        i++;
      }
  
      if (startI < i || centerJ < i) {
        return false;
      }
  
      // Continue up, left finding white space
      while (startI >= i && centerJ >= i && !image.get(centerJ - i, startI - i) &&
             stateCount[1] <= maxCount) {
        stateCount[1]++;
        i++;
      }
  
      // If already too many modules in this state or ran off the edge:
      if (startI < i || centerJ < i || stateCount[1] > maxCount) {
        return false;
      }
  
      // Continue up, left finding black border
      while (startI >= i && centerJ >= i && image.get(centerJ - i, startI - i) &&
             stateCount[0] <= maxCount) {
        stateCount[0]++;
        i++;
      }
      if (stateCount[0] > maxCount) {
         return false;
      }
  
      int maxI = image.getHeight();
      int maxJ = image.getWidth();
  
      // Now also count down, right from center
      i = 1;
      while (startI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, startI + i)) {
        stateCount[2]++;
        i++;
      }
  
      // Ran off the edge?
      if (startI + i >= maxI || centerJ + i >= maxJ) {
         return false;
      }
  
      while (startI + i < maxI && centerJ + i < maxJ && !image.get(centerJ + i, startI + i) &&
             stateCount[3] < maxCount) {
        stateCount[3]++;
        i++;
      }
  
      if (startI + i >= maxI || centerJ + i >= maxJ || stateCount[3] >= maxCount) {
        return false;
      }
  
      while (startI + i < maxI && centerJ + i < maxJ && image.get(centerJ + i, startI + i) &&
             stateCount[4] < maxCount) {
        stateCount[4]++;
        i++;
      }
  
      if (stateCount[4] >= maxCount) {
        return false;
     }
  
      // If we found a finder-pattern-like section, but its size is more than 100% different than
      // the original, assume it's a false positive
      int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
      return
          Math.abs(stateCountTotal - originalStateCountTotal) < 2 * originalStateCountTotal &&
          foundPatternCross(stateCount);
    }
  
    /**
     * <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.
     * And then we cross-cross-cross check with another diagonal scan.</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
     * @param pureBarcode true if in "pure barcode" mode
     * @return true if a finder pattern candidate was found this time
     */
    protected final boolean handlePossibleCenter(int[] stateCount, int i, int j, boolean pureBarcode) {
      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) &&
            (!pureBarcode || crossCheckDiagonal((int) centerI, (int) centerJ, stateCount[2], stateCountTotal))) {
          float estimatedModuleSize = (float) 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;
      }
      ResultPoint 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 / (float) 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 / (float) 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 / (float) 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 final class FurthestFromAverageComparator implements Comparator<FinderPattern>, Serializable {
      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 final class CenterComparator implements Comparator<FinderPattern>, Serializable {
      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;
        } else {
          return center2.getCount() - center1.getCount();
        }
      }
    }
  
  }
  