getDataBlocks static method

List<DataBlock> getDataBlocks(Uint8List rawCodewords, Version version, ErrorCorrectionLevel ecLevel)

When QR Codes use multiple data blocks, they are actually interleaved. That is, the first byte of data block 1 to n is written, then the second bytes, and so on. This method will separate the data into original blocks.

@param rawCodewords bytes as read directly from the QR Code @param version version of the QR Code @param ecLevel error-correction level of the QR Code @return DataBlocks containing original bytes, "de-interleaved" from representation in the QR Code

Implementation

static List<DataBlock> getDataBlocks(
  Uint8List rawCodewords,
  Version version,
  ErrorCorrectionLevel ecLevel,
) {
  if (rawCodewords.length != version.totalCodewords) {
    throw ArgumentError();
  }

  // Figure out the number and size of data blocks used by this version and
  // error correction level
  final ecBlocks = version.getECBlocksForLevel(ecLevel);

  // First count the total number of data blocks
  //int totalBlocks = 0;
  final ecBlockArray = ecBlocks.ecBlocks;
  //for (ECB ecBlock in ecBlockArray) {
  //  totalBlocks += ecBlock.getCount();
  //}

  // Now establish DataBlocks of the appropriate size and number of data codewords
  final result = <DataBlock>[];
  for (ECB ecBlock in ecBlockArray) {
    for (int i = 0; i < ecBlock.count; i++) {
      final numDataCodewords = ecBlock.dataCodewords;
      final numBlockCodewords =
          ecBlocks.ecCodewordsPerBlock + numDataCodewords;
      result.add(DataBlock._(numDataCodewords, Uint8List(numBlockCodewords)));
    }
  }
  final numResultBlocks = result.length;

  // All blocks have the same amount of data, except that the last n
  // (where n may be 0) have 1 more byte. Figure out where these start.
  final shorterBlocksTotalCodewords = result[0]._codewords.length;
  int longerBlocksStartAt = result.length - 1;
  while (longerBlocksStartAt >= 0) {
    final numCodewords = result[longerBlocksStartAt]._codewords.length;
    if (numCodewords == shorterBlocksTotalCodewords) {
      break;
    }
    longerBlocksStartAt--;
  }
  longerBlocksStartAt++;

  final shorterBlocksNumDataCodewords =
      shorterBlocksTotalCodewords - ecBlocks.ecCodewordsPerBlock;
  // The last elements of result may be 1 element longer;
  // first fill out as many elements as all of them have
  int rawCodewordsOffset = 0;
  for (int i = 0; i < shorterBlocksNumDataCodewords; i++) {
    for (int j = 0; j < numResultBlocks; j++) {
      result[j]._codewords[i] = rawCodewords[rawCodewordsOffset++];
    }
  }
  // Fill out the last data block in the longer ones
  for (int j = longerBlocksStartAt; j < numResultBlocks; j++) {
    result[j]._codewords[shorterBlocksNumDataCodewords] =
        rawCodewords[rawCodewordsOffset++];
  }
  // Now add in error correction blocks
  final max = result[0]._codewords.length;
  for (int i = shorterBlocksNumDataCodewords; i < max; i++) {
    for (int j = 0; j < numResultBlocks; j++) {
      final iOffset = j < longerBlocksStartAt ? i : i + 1;
      result[j]._codewords[iOffset] = rawCodewords[rawCodewordsOffset++];
    }
  }
  return result;
}