/*
 * Copyright 2008 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.NotFoundException;
import com.google.zxing.common.BitArray;

/**
 * <p>Implements decoding of the EAN-13 format.</p>
 *
 * @author dswitkin@google.com (Daniel Switkin)
 * @author Sean Owen
 * @author alasdair@google.com (Alasdair Mackintosh)
 */
public final class EAN13Reader extends UPCEANReader {

  // For an EAN-13 barcode, the first digit is represented by the parities used
  // to encode the next six digits, according to the table below. For example,
  // if the barcode is 5 123456 789012 then the value of the first digit is
  // signified by using odd for '1', even for '2', even for '3', odd for '4',
  // odd for '5', and even for '6'. See http://en.wikipedia.org/wiki/EAN-13
  //
  //                Parity of next 6 digits
  //    Digit   0     1     2     3     4     5
  //       0    Odd   Odd   Odd   Odd   Odd   Odd
  //       1    Odd   Odd   Even  Odd   Even  Even
  //       2    Odd   Odd   Even  Even  Odd   Even
  //       3    Odd   Odd   Even  Even  Even  Odd
  //       4    Odd   Even  Odd   Odd   Even  Even
  //       5    Odd   Even  Even  Odd   Odd   Even
  //       6    Odd   Even  Even  Even  Odd   Odd
  //       7    Odd   Even  Odd   Even  Odd   Even
  //       8    Odd   Even  Odd   Even  Even  Odd
  //       9    Odd   Even  Even  Odd   Even  Odd
  //
  // Note that the encoding for '0' uses the same parity as a UPC barcode. Hence
  // a UPC barcode can be converted to an EAN-13 barcode by prepending a 0.
  //
  // The encoding is represented by the following array, which is a bit pattern
  // using Odd = 0 and Even = 1. For example, 5 is represented by:
  //
  //              Odd Even Even Odd Odd Even
  // in binary:
  //                0    1    1   0   0    1   == 0x19
  //
  static final int[] FIRST_DIGIT_ENCODINGS = {
      0x00, 0x0B, 0x0D, 0xE, 0x13, 0x19, 0x1C, 0x15, 0x16, 0x1A
  };

  private final int[] decodeMiddleCounters;

  public EAN13Reader() {
    decodeMiddleCounters = new int[4];
  }

  @Override
  protected int decodeMiddle(BitArray row,
                             int[] startRange,
                             StringBuilder resultString) throws NotFoundException {
    int[] counters = decodeMiddleCounters;
    counters[0] = 0;
    counters[1] = 0;
    counters[2] = 0;
    counters[3] = 0;
    int end = row.getSize();
    int rowOffset = startRange[1];

    int lgPatternFound = 0;

    for (int x = 0; x < 6 && rowOffset < end; x++) {
      int bestMatch = decodeDigit(row, counters, rowOffset, L_AND_G_PATTERNS);
      resultString.append((char) ('0' + bestMatch % 10));
      for (int counter : counters) {
        rowOffset += counter;
      }
      if (bestMatch >= 10) {
        lgPatternFound |= 1 << (5 - x);
      }
    }

    determineFirstDigit(resultString, lgPatternFound);

    int[] middleRange = findGuardPattern(row, rowOffset, true, MIDDLE_PATTERN);
    rowOffset = middleRange[1];

    for (int x = 0; x < 6 && rowOffset < end; x++) {
      int bestMatch = decodeDigit(row, counters, rowOffset, L_PATTERNS);
      resultString.append((char) ('0' + bestMatch));
      for (int counter : counters) {
        rowOffset += counter;
      }
    }

    return rowOffset;
  }

  @Override
  BarcodeFormat getBarcodeFormat() {
    return BarcodeFormat.EAN_13;
  }

  /**
   * Based on pattern of odd-even ('L' and 'G') patterns used to encoded the explicitly-encoded
   * digits in a barcode, determines the implicitly encoded first digit and adds it to the
   * result string.
   *
   * @param resultString string to insert decoded first digit into
   * @param lgPatternFound int whose bits indicates the pattern of odd/even L/G patterns used to
   *  encode digits
   * @throws NotFoundException if first digit cannot be determined
   */
  private static void determineFirstDigit(StringBuilder resultString, int lgPatternFound)
      throws NotFoundException {
    for (int d = 0; d < 10; d++) {
      if (lgPatternFound == FIRST_DIGIT_ENCODINGS[d]) {
        resultString.insert(0, (char) ('0' + d));
        return;
      }
    }
    throw NotFoundException.getNotFoundInstance();
  }

}
