invert method

Delta invert(Delta base)

Inverts this delta against base.

Returns new delta which negates effect of this delta when applied to base. This is an equivalent of "undo" operation on deltas.

Implementation

Delta invert(Delta base) {
  final inverted = new Delta();
  if (base.isEmpty) return inverted;

  int baseIndex = 0;
  for (final op in _operations) {
    if (op.isInsert) {
      inverted.delete(op.length!);
    } else if (op.isRetain && op.isPlain) {
      inverted.retain(op.length!, null);
      baseIndex += op.length!;
    } else if (op.isDelete || (op.isRetain && op.isNotPlain)) {
      final length = op.length!;
      final sliceDelta = base.slice(baseIndex, baseIndex + length);
      sliceDelta.toList().forEach((baseOp) {
        if (op.isDelete) {
          inverted.push(baseOp);
        } else if (op.isRetain && op.isNotPlain) {
          var invertAttr = invertAttributes(op.attributes, baseOp.attributes);
          inverted.retain(baseOp.length!, invertAttr.isEmpty ? null : invertAttr);
        }
      });
      baseIndex += length;
    } else {
      throw StateError("Unreachable");
    }
  }
  inverted.trim();
  return inverted;
}