sdk/lib/convert/converter.dart

// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.convert;

/**
 * A [Converter] converts data from one representation into another.
 *
 * It is recommended that implementations of `Converter` extend this class,
 * to inherit any further methods that may be added to the class.
 */
abstract class Converter<S, T> implements StreamTransformer<S, T> {
  const Converter();

  /**
   * Converts [input] and returns the result of the conversion.
   */
  T convert(S input);

  /**
   * Fuses `this` with [other].
   *
   * Encoding with the resulting converter is equivalent to converting with
   * `this` before converting with `other`.
   */
  Converter<S, TT> fuse<TT>(Converter<T, TT> other) {
    return new _FusedConverter<S, T, TT>(this, other);
  }

  /**
   * Starts a chunked conversion.
   *
   * The returned sink serves as input for the long-running conversion. The
   * given [sink] serves as output.
   */
  Sink/*<S>*/ startChunkedConversion(Sink/*<T>*/ sink) {
    throw new UnsupportedError(
        "This converter does not support chunked conversions: $this");
  }

  Stream<T> bind(Stream<S> stream) {
    return new Stream<T>.eventTransformed(
        stream, (EventSink sink) => new _ConverterStreamEventSink(this, sink));
  }
}

/**
 * Fuses two converters.
 *
 * For a non-chunked conversion converts the input in sequence.
 */
class _FusedConverter<S, M, T> extends Converter<S, T>
    implements ChunkedConverter<S, T, S, T> {
  final Converter<S, M> _first;
  final Converter<M, T> _second;

  _FusedConverter(this._first, this._second);

  T convert(S input) => _second.convert(_first.convert(input));

  Sink/*<S>*/ startChunkedConversion(Sink/*<T>*/ sink) {
    return _first.startChunkedConversion(_second.startChunkedConversion(sink));
  }
}