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// Copyright (c) 2016, 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.
import 'dart:async';
import 'stream_sink_transformer/handler_transformer.dart';
import 'stream_sink_transformer/stream_transformer_wrapper.dart';
import 'stream_sink_transformer/typed.dart';
/// A [StreamSinkTransformer] transforms the events being passed to a sink.
/// This works on the same principle as a [StreamTransformer]. Each transformer
/// defines a [bind] method that takes in the original [StreamSink] and returns
/// the transformed version. However, where a [StreamTransformer] transforms
/// events after they leave the stream, this transforms them before they enter
/// the sink.
/// Transformers must be able to have `bind` called used multiple times.
abstract class StreamSinkTransformer<S, T> {
/// Creates a [StreamSinkTransformer] that transforms events and errors
/// using [transformer].
/// This is equivalent to piping all events from the outer sink through a
/// stream transformed by [transformer] and from there into the inner sink.
const factory StreamSinkTransformer.fromStreamTransformer(
StreamTransformer<S, T> transformer) = StreamTransformerWrapper<S, T>;
/// Creates a [StreamSinkTransformer] that delegates events to the given
/// handlers.
/// The handlers work exactly as they do for [StreamTransformer.fromHandlers].
/// They're called for each incoming event, and any actions on the sink
/// they're passed are forwarded to the inner sink. If a handler is omitted,
/// the event is passed through unaltered.
factory StreamSinkTransformer.fromHandlers(
{void Function(S, EventSink<T>) handleData,
void Function(Object, StackTrace, EventSink<T>) handleError,
void Function(EventSink<T>) handleDone}) {
return HandlerTransformer<S, T>(handleData, handleError, handleDone);
/// Transforms the events passed to [sink].
/// Creates a new sink. When events are passed to the returned sink, it will
/// transform them and pass the transformed versions to [sink].
StreamSink<S> bind(StreamSink<T> sink);
/// Creates a wrapper that coerces the type of [transformer].
/// This soundly converts a [StreamSinkTransformer] to a
/// `StreamSinkTransformer<S, T>`, regardless of its original generic type.
/// This means that calls to [StreamSink.add] on the returned sink may throw a
/// [CastError] if the argument type doesn't match the reified type of the
/// sink.
static StreamSinkTransformer<S, T> typed<S, T>(
StreamSinkTransformer transformer) =>
transformer is StreamSinkTransformer<S, T>
? transformer
: TypeSafeStreamSinkTransformer(transformer);