decode method

Fugue<String> decode(Uint8List bytes)

Decode a buffer produced by encode.

Implementation

Fugue<String> decode(Uint8List bytes) {
  final r = _Reader(bytes);
  final version = r.u8();
  if (version != 1) {
    throw FormatException('Unsupported Fugue binary version: $version');
  }
  final replicaCount = r.varint();
  final dict = <String>[
    for (var i = 0; i < replicaCount; i++) utf8.decode(r.take(r.varint())),
  ];

  final blockCount = r.varint();
  final blocks = <(Dot, Dot, Side, List<String>, List<int>)>[];
  for (var i = 0; i < blockCount; i++) {
    final startReplica = dict[r.varint()];
    final startCounter = r.varint();
    final flags = r.u8();
    final side = (flags & 1) == 1 ? Side.right : Side.left;
    final origin = (flags & 0x80) != 0;
    final Dot parent;
    if (origin) {
      parent = Dot.origin;
    } else {
      final parentReplica = dict[r.varint()];
      final parentCounter = r.varint();
      parent = Dot(parentCounter, parentReplica);
    }
    final text = utf8.decode(r.take(r.varint()));
    final elementCount = r.varint();
    final values = <String>[
      for (final rune in text.runes) String.fromCharCode(rune),
    ];
    // The run is recovered by rune-splitting, which only round-trips when
    // every element was a single Unicode scalar (the codec's assumption).
    // A multi-rune element (e.g. an emoji grapheme cluster) would split
    // into several runes here, silently shifting every later element's dot.
    // Cross-check against the stored count to fail loudly instead.
    if (values.length != elementCount) {
      throw FormatException(
        'element count mismatch: block encoded $elementCount elements '
        'but decoded ${values.length} runes — values must be single '
        'Unicode scalars',
      );
    }
    final delCount = r.varint();
    final del = <int>[for (var j = 0; j < delCount * 2; j++) r.varint()];
    blocks.add((Dot(startCounter, startReplica), parent, side, values, del));
  }
  return Fugue.fromRawBlocks<String>(blocks);
}