/*
 * Copyright 2010 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.oned;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.ChecksumException;
import com.google.zxing.DecodeHintType;
import com.google.zxing.FormatException;
import com.google.zxing.NotFoundException;
import com.google.zxing.Result;
import com.google.zxing.ResultPoint;
import com.google.zxing.common.BitArray;

import java.util.Map;

/**
 * <p>Decodes Code 93 barcodes.</p>
 *
 * @author Sean Owen
 * @see Code39Reader
 */
public final class Code93Reader extends OneDReader {

  // Note that 'abcd' are dummy characters in place of control characters.
  private static final String ALPHABET_STRING = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%abcd*";
  private static final char[] ALPHABET = ALPHABET_STRING.toCharArray();

  /**
   * These represent the encodings of characters, as patterns of wide and narrow bars.
   * The 9 least-significant bits of each int correspond to the pattern of wide and narrow.
   */
  private static final int[] CHARACTER_ENCODINGS = {
      0x114, 0x148, 0x144, 0x142, 0x128, 0x124, 0x122, 0x150, 0x112, 0x10A, // 0-9
      0x1A8, 0x1A4, 0x1A2, 0x194, 0x192, 0x18A, 0x168, 0x164, 0x162, 0x134, // A-J
      0x11A, 0x158, 0x14C, 0x146, 0x12C, 0x116, 0x1B4, 0x1B2, 0x1AC, 0x1A6, // K-T
      0x196, 0x19A, 0x16C, 0x166, 0x136, 0x13A, // U-Z
      0x12E, 0x1D4, 0x1D2, 0x1CA, 0x16E, 0x176, 0x1AE, // - - %
      0x126, 0x1DA, 0x1D6, 0x132, 0x15E, // Control chars? $-*
  };
  private static final int ASTERISK_ENCODING = CHARACTER_ENCODINGS[47];

  @Override
  public Result decodeRow(int rowNumber, BitArray row, Map<DecodeHintType,?> hints)
      throws NotFoundException, ChecksumException, FormatException {

    int[] start = findAsteriskPattern(row);
    // Read off white space    
    int nextStart = row.getNextSet(start[1]);
    int end = row.getSize();

    StringBuilder result = new StringBuilder(20);
    int[] counters = new int[6];
    char decodedChar;
    int lastStart;
    do {
      recordPattern(row, nextStart, counters);
      int pattern = toPattern(counters);
      if (pattern < 0) {
        throw NotFoundException.getNotFoundInstance();
      }
      decodedChar = patternToChar(pattern);
      result.append(decodedChar);
      lastStart = nextStart;
      for (int counter : counters) {
        nextStart += counter;
      }
      // Read off white space
      nextStart = row.getNextSet(nextStart);
    } while (decodedChar != '*');
    result.deleteCharAt(result.length() - 1); // remove asterisk

    // Should be at least one more black module
    if (nextStart == end || !row.get(nextStart)) {
      throw NotFoundException.getNotFoundInstance();
    }

    if (result.length() < 2) {
      // false positive -- need at least 2 checksum digits
      throw NotFoundException.getNotFoundInstance();
    }

    checkChecksums(result);
    // Remove checksum digits
    result.setLength(result.length() - 2);

    String resultString = decodeExtended(result);

    float left = (float) (start[1] + start[0]) / 2.0f;
    float right = (float) (nextStart + lastStart) / 2.0f;
    return new Result(
        resultString,
        null,
        new ResultPoint[]{
            new ResultPoint(left, (float) rowNumber),
            new ResultPoint(right, (float) rowNumber)},
        BarcodeFormat.CODE_93);

  }

  private static int[] findAsteriskPattern(BitArray row) throws NotFoundException {
    int width = row.getSize();
    int rowOffset = row.getNextSet(0);

    int counterPosition = 0;
    int[] counters = new int[6];
    int patternStart = rowOffset;
    boolean isWhite = false;
    int patternLength = counters.length;

    for (int i = rowOffset; i < width; i++) {
      if (row.get(i) ^ isWhite) {
        counters[counterPosition]++;
      } else {
        if (counterPosition == patternLength - 1) {
          if (toPattern(counters) == ASTERISK_ENCODING) {
            return new int[]{patternStart, i};
          }
          patternStart += counters[0] + counters[1];
          System.arraycopy(counters, 2, counters, 0, patternLength - 2);
          counters[patternLength - 2] = 0;
          counters[patternLength - 1] = 0;
          counterPosition--;
        } else {
          counterPosition++;
        }
        counters[counterPosition] = 1;
        isWhite = !isWhite;
      }
    }
    throw NotFoundException.getNotFoundInstance();
  }

  private static int toPattern(int[] counters) {
    int max = counters.length;
    int sum = 0;
    for (int counter : counters) {
      sum += counter;
    }
    int pattern = 0;
    for (int i = 0; i < max; i++) {
      int scaledShifted = (counters[i] << INTEGER_MATH_SHIFT) * 9 / sum;
      int scaledUnshifted = scaledShifted >> INTEGER_MATH_SHIFT;
      if ((scaledShifted & 0xFF) > 0x7F) {
        scaledUnshifted++;
      }
      if (scaledUnshifted < 1 || scaledUnshifted > 4) {
        return -1;
      }
      if ((i & 0x01) == 0) {
        for (int j = 0; j < scaledUnshifted; j++) {
          pattern = (pattern << 1) | 0x01;
        }
      } else {
        pattern <<= scaledUnshifted;
      }
    }
    return pattern;
  }

  private static char patternToChar(int pattern) throws NotFoundException {
    for (int i = 0; i < CHARACTER_ENCODINGS.length; i++) {
      if (CHARACTER_ENCODINGS[i] == pattern) {
        return ALPHABET[i];
      }
    }
    throw NotFoundException.getNotFoundInstance();
  }

  private static String decodeExtended(CharSequence encoded) throws FormatException {
    int length = encoded.length();
    StringBuilder decoded = new StringBuilder(length);
    for (int i = 0; i < length; i++) {
      char c = encoded.charAt(i);
      if (c >= 'a' && c <= 'd') {
        if (i >= length - 1) {
          throw FormatException.getFormatInstance();
        }
        char next = encoded.charAt(i + 1);
        char decodedChar = '\0';
        switch (c) {
          case 'd':
            // +A to +Z map to a to z
            if (next >= 'A' && next <= 'Z') {
              decodedChar = (char) (next + 32);
            } else {
              throw FormatException.getFormatInstance();
            }
            break;
          case 'a':
            // $A to $Z map to control codes SH to SB
            if (next >= 'A' && next <= 'Z') {
              decodedChar = (char) (next - 64);
            } else {
              throw FormatException.getFormatInstance();
            }
            break;
          case 'b':
            // %A to %E map to control codes ESC to US
            if (next >= 'A' && next <= 'E') {
              decodedChar = (char) (next - 38);
            } else if (next >= 'F' && next <= 'W') {
              decodedChar = (char) (next - 11);
            } else {
              throw FormatException.getFormatInstance();
            }
            break;
          case 'c':
            // /A to /O map to ! to , and /Z maps to :
            if (next >= 'A' && next <= 'O') {
              decodedChar = (char) (next - 32);
            } else if (next == 'Z') {
              decodedChar = ':';
            } else {
              throw FormatException.getFormatInstance();
            }
            break;
        }
        decoded.append(decodedChar);
        // bump up i again since we read two characters
        i++;
      } else {
        decoded.append(c);
      }
    }
    return decoded.toString();
  }

  private static void checkChecksums(CharSequence result) throws ChecksumException {
    int length = result.length();
    checkOneChecksum(result, length - 2, 20);
    checkOneChecksum(result, length - 1, 15);
  }

  private static void checkOneChecksum(CharSequence result, int checkPosition, int weightMax)
      throws ChecksumException {
    int weight = 1;
    int total = 0;
    for (int i = checkPosition - 1; i >= 0; i--) {
      total += weight * ALPHABET_STRING.indexOf(result.charAt(i));
      if (++weight > weightMax) {
        weight = 1;
      }
    }
    if (result.charAt(checkPosition) != ALPHABET[total % 47]) {
      throw ChecksumException.getChecksumInstance();
    }
  }

}
