convert method

@override Iterable<bool> convert(String data)

Actual barcode computation method, returns a stream of bool which represents the presence or absence of a bar

Implementation

@override
Iterable<bool> convert(String data) sync* {
  if (data.length <= 8) {
    // Try to convert UPC-E to UPC-A
    data = upceToUpca(data);
  }

  data = checkLength(data, maxLength);
  final first = data.codeUnitAt(0);
  final last = data.codeUnitAt(11);

  try {
    data = upcaToUpce(data);
  } on BarcodeException {
    if (fallback) {
      yield* const BarcodeUpcA().convert(data);
      return;
    }
    rethrow;
  }

  // Start
  yield* add(BarcodeMaps.eanStartEnd, 3);

  final parityRow = BarcodeMaps.upce[last];
  final parity = first == 0x30 ? parityRow : parityRow! ^ 0x3f;

  var index = 0;
  for (var code in data.codeUnits) {
    final codes = BarcodeMaps.ean[code];

    if (codes == null) {
      throw BarcodeException(
          'Unable to encode "${String.fromCharCode(code)}" to $name Barcode');
    }

    yield* add(codes[(parity! >> index) & 1 == 0 ? 1 : 0], 7);
    index++;
  }

  // Stop
  yield* add(BarcodeMaps.eanEndUpcE, 6);
}