getDataBlocks static method

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

When Data Matrix Codes use multiple data blocks, they actually interleave the bytes of each of them. 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 Data Matrix Code @param version version of the Data Matrix Code @return DataBlocks containing original bytes, "de-interleaved" from representation in the Data Matrix Code

Implementation

static List<DataBlock> getDataBlocks(
  Uint8List rawCodewords,
  Version version,
) {
  // Figure out the number and size of data blocks used by this version
  final ecBlocks = version.ecBlocks;

  // 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>[];
  //int numResultBlocks = 0;
  for (ECB ecBlock in ecBlockArray) {
    for (int i = 0; i < ecBlock.count; i++) {
      final numDataCodewords = ecBlock.dataCodewords;
      final numBlockCodewords = ecBlocks.ecCodewords + 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 less byte. Figure out where these start.
  // TODO(bbrown): There is only one case where there is a difference for Data Matrix for size 144
  final longerBlocksTotalCodewords = result[0]._codewords.length;
  //int shorterBlocksTotalCodewords = longerBlocksTotalCodewords - 1;

  final longerBlocksNumDataCodewords =
      longerBlocksTotalCodewords - ecBlocks.ecCodewords;
  final shorterBlocksNumDataCodewords = longerBlocksNumDataCodewords - 1;
  // The last elements of result may be 1 element shorter for 144 matrix
  // first fill out as many elements as all of them have minus 1
  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
  final specialVersion = version.versionNumber == 24;
  final numLongerBlocks = specialVersion ? 8 : numResultBlocks;
  for (int j = 0; j < numLongerBlocks; j++) {
    result[j]._codewords[longerBlocksNumDataCodewords - 1] =
        rawCodewords[rawCodewordsOffset++];
  }

  // Now add in error correction blocks
  final max = result[0]._codewords.length;
  for (int i = longerBlocksNumDataCodewords; i < max; i++) {
    for (int j = 0; j < numResultBlocks; j++) {
      final jOffset = specialVersion ? (j + 8) % numResultBlocks : j;
      final iOffset = specialVersion && jOffset > 7 ? i - 1 : i;
      result[jOffset]._codewords[iOffset] =
          rawCodewords[rawCodewordsOffset++];
    }
  }

  if (rawCodewordsOffset != rawCodewords.length) {
    throw ArgumentError();
  }

  return result;
}