// Copyright (c) 2012, 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.async;

/**
 * Utility function to attach a stack trace to an [error]  if it doesn't have
 * one already.
 */
_asyncError(Object error, StackTrace stackTrace) {
  if (stackTrace == null) return error;
  if (getAttachedStackTrace(error) != null) return error;
  _attachStackTrace(error, stackTrace);
  return error;
}

/** Runs user code and takes actions depending on success or failure. */
_runUserCode(userCode(),
             onSuccess(value),
             onError(error, StackTrace stackTrace)) {
  try {
    onSuccess(userCode());
  } catch (e, s) {
    onError(_asyncError(e, s), s);
  }
}

/** Helper function to cancel a subscription and wait for the potential future,
  before completing with an error. */
void _cancelAndError(StreamSubscription subscription,
                     _Future future,
                     error,
                     StackTrace stackTrace) {
  var cancelFuture = subscription.cancel();
  if (cancelFuture is Future) {
    cancelFuture.whenComplete(() => future._completeError(error, stackTrace));
  } else {
    future._completeError(error, stackTrace);
  }
}

/** Helper function to make an onError argument to [_runUserCode]. */
_cancelAndErrorClosure(StreamSubscription subscription, _Future future) =>
  ((error, StackTrace stackTrace) => _cancelAndError(
      subscription, future, error, stackTrace));

/** Helper function to cancel a subscription and wait for the potential future,
  before completing with a value. */
void _cancelAndValue(StreamSubscription subscription, _Future future, value) {
  var cancelFuture = subscription.cancel();
  if (cancelFuture is Future) {
    cancelFuture.whenComplete(() => future._complete(value));
  } else {
    future._complete(value);
  }
}


/**
 * A [Stream] that forwards subscriptions to another stream.
 *
 * This stream implements [Stream], but forwards all subscriptions
 * to an underlying stream, and wraps the returned subscription to
 * modify the events on the way.
 *
 * This class is intended for internal use only.
 */
abstract class _ForwardingStream<S, T> extends Stream<T> {
  final Stream<S> _source;

  _ForwardingStream(this._source);

  bool get isBroadcast => _source.isBroadcast;

  StreamSubscription<T> listen(void onData(T value),
                              { Function onError,
                                void onDone(),
                                bool cancelOnError }) {
    cancelOnError = identical(true, cancelOnError);
    StreamSubscription<T> result = _createSubscription(cancelOnError);
    result.onData(onData);
    result.onError(onError);
    result.onDone(onDone);
    return result;
  }

  StreamSubscription<T> _createSubscription(bool cancelOnError) {
    return new _ForwardingStreamSubscription<S, T>(this, cancelOnError);
  }

  // Override the following methods in subclasses to change the behavior.

  void _handleData(S data, _EventSink<T> sink) {
    var outputData = data;
    sink._add(outputData);
  }

  void _handleError(error, StackTrace stackTrace, _EventSink<T> sink) {
    sink._addError(error, stackTrace);
  }

  void _handleDone(_EventSink<T> sink) {
    sink._close();
  }
}

/**
 * Abstract superclass for subscriptions that forward to other subscriptions.
 */
class _ForwardingStreamSubscription<S, T>
    extends _BufferingStreamSubscription<T> {
  final _ForwardingStream<S, T> _stream;

  StreamSubscription<S> _subscription;

  _ForwardingStreamSubscription(this._stream, bool cancelOnError)
      : super(cancelOnError) {
    _subscription = _stream._source.listen(_handleData,
                                           onError: _handleError,
                                           onDone: _handleDone);
  }

  // _StreamSink interface.
  // Transformers sending more than one event have no way to know if the stream
  // is canceled or closed after the first, so we just ignore remaining events.

  void _add(T data) {
    if (_isClosed) return;
    super._add(data);
  }

  void _addError(Object error, StackTrace stackTrace) {
    if (_isClosed) return;
    super._addError(error, stackTrace);
  }

  // StreamSubscription callbacks.

  void _onPause() {
    if (_subscription == null) return;
    _subscription.pause();
  }

  void _onResume() {
    if (_subscription == null) return;
    _subscription.resume();
  }

  Future _onCancel() {
    if (_subscription != null) {
      StreamSubscription subscription = _subscription;
      _subscription = null;
      subscription.cancel();
    }
    return null;
  }

  // Methods used as listener on source subscription.

  void _handleData(S data) {
    _stream._handleData(data, this);
  }

  void _handleError(error, StackTrace stackTrace) {
    _stream._handleError(error, stackTrace, this);
  }

  void _handleDone() {
    _stream._handleDone(this);
  }
}

// -------------------------------------------------------------------
// Stream transformers used by the default Stream implementation.
// -------------------------------------------------------------------

typedef bool _Predicate<T>(T value);

class _WhereStream<T> extends _ForwardingStream<T, T> {
  final _Predicate<T> _test;

  _WhereStream(Stream<T> source, bool test(T value))
      : _test = test, super(source);

  void _handleData(T inputEvent, _EventSink<T> sink) {
    bool satisfies;
    try {
      satisfies = _test(inputEvent);
    } catch (e, s) {
      sink._addError(_asyncError(e, s), s);
      return;
    }
    if (satisfies) {
      sink._add(inputEvent);
    }
  }
}


typedef T _Transformation<S, T>(S value);

/**
 * A stream pipe that converts data events before passing them on.
 */
class _MapStream<S, T> extends _ForwardingStream<S, T> {
  final _Transformation _transform;

  _MapStream(Stream<S> source, T transform(S event))
      : this._transform = transform, super(source);

  void _handleData(S inputEvent, _EventSink<T> sink) {
    T outputEvent;
    try {
      outputEvent = _transform(inputEvent);
    } catch (e, s) {
      sink._addError(_asyncError(e, s), s);
      return;
    }
    sink._add(outputEvent);
  }
}

/**
 * A stream pipe that converts data events before passing them on.
 */
class _ExpandStream<S, T> extends _ForwardingStream<S, T> {
  final _Transformation<S, Iterable<T>> _expand;

  _ExpandStream(Stream<S> source, Iterable<T> expand(S event))
      : this._expand = expand, super(source);

  void _handleData(S inputEvent, _EventSink<T> sink) {
    try {
      for (T value in _expand(inputEvent)) {
        sink._add(value);
      }
    } catch (e, s) {
      // If either _expand or iterating the generated iterator throws,
      // we abort the iteration.
      sink._addError(_asyncError(e, s), s);
    }
  }
}


typedef bool _ErrorTest(error);

/**
 * A stream pipe that converts or disposes error events
 * before passing them on.
 */
class _HandleErrorStream<T> extends _ForwardingStream<T, T> {
  final Function _transform;
  final _ErrorTest _test;

  _HandleErrorStream(Stream<T> source,
                     Function onError,
                     bool test(error))
      : this._transform = onError, this._test = test, super(source);

  void _handleError(Object error, StackTrace stackTrace, _EventSink<T> sink) {
    bool matches = true;
    if (_test != null) {
      try {
        matches = _test(error);
      } catch (e, s) {
        sink._addError(_asyncError(e, s), s);
        return;
      }
    }
    if (matches) {
      try {
        _invokeErrorHandler(_transform, error, stackTrace);
      } catch (e, s) {
        if (identical(e, error)) {
          sink._addError(error, stackTrace);
        } else {
          sink._addError(_asyncError(e, s), s);
        }
        return;
      }
    } else {
      sink._addError(error, stackTrace);
    }
  }
}


class _TakeStream<T> extends _ForwardingStream<T, T> {
  int _remaining;

  _TakeStream(Stream<T> source, int count)
      : this._remaining = count, super(source) {
    // This test is done early to avoid handling an async error
    // in the _handleData method.
    if (count is! int) throw new ArgumentError(count);
  }

  void _handleData(T inputEvent, _EventSink<T> sink) {
    if (_remaining > 0) {
      sink._add(inputEvent);
      _remaining -= 1;
      if (_remaining == 0) {
        // Closing also unsubscribes all subscribers, which unsubscribes
        // this from source.
        sink._close();
      }
    }
  }
}


class _TakeWhileStream<T> extends _ForwardingStream<T, T> {
  final _Predicate<T> _test;

  _TakeWhileStream(Stream<T> source, bool test(T value))
      : this._test = test, super(source);

  void _handleData(T inputEvent, _EventSink<T> sink) {
    bool satisfies;
    try {
      satisfies = _test(inputEvent);
    } catch (e, s) {
      sink._addError(_asyncError(e, s), s);
      // The test didn't say true. Didn't say false either, but we stop anyway.
      sink._close();
      return;
    }
    if (satisfies) {
      sink._add(inputEvent);
    } else {
      sink._close();
    }
  }
}

class _SkipStream<T> extends _ForwardingStream<T, T> {
  int _remaining;

  _SkipStream(Stream<T> source, int count)
      : this._remaining = count, super(source) {
    // This test is done early to avoid handling an async error
    // in the _handleData method.
    if (count is! int || count < 0) throw new ArgumentError(count);
  }

  void _handleData(T inputEvent, _EventSink<T> sink) {
    if (_remaining > 0) {
      _remaining--;
      return;
    }
    sink._add(inputEvent);
  }
}

class _SkipWhileStream<T> extends _ForwardingStream<T, T> {
  final _Predicate<T> _test;
  bool _hasFailed = false;

  _SkipWhileStream(Stream<T> source, bool test(T value))
      : this._test = test, super(source);

  void _handleData(T inputEvent, _EventSink<T> sink) {
    if (_hasFailed) {
      sink._add(inputEvent);
      return;
    }
    bool satisfies;
    try {
      satisfies = _test(inputEvent);
    } catch (e, s) {
      sink._addError(_asyncError(e, s), s);
      // A failure to return a boolean is considered "not matching".
      _hasFailed = true;
      return;
    }
    if (!satisfies) {
      _hasFailed = true;
      sink._add(inputEvent);
    }
  }
}

typedef bool _Equality<T>(T a, T b);

class _DistinctStream<T> extends _ForwardingStream<T, T> {
  static var _SENTINEL = new Object();

  _Equality<T> _equals;
  var _previous = _SENTINEL;

  _DistinctStream(Stream<T> source, bool equals(T a, T b))
      : _equals = equals, super(source);

  void _handleData(T inputEvent, _EventSink<T> sink) {
    if (identical(_previous, _SENTINEL)) {
      _previous = inputEvent;
      return sink._add(inputEvent);
    } else {
      bool isEqual;
      try {
        if (_equals == null) {
          isEqual = (_previous == inputEvent);
        } else {
          isEqual = _equals(_previous, inputEvent);
        }
      } catch (e, s) {
        sink._addError(_asyncError(e, s), s);
        return null;
      }
      if (!isEqual) {
        sink._add(inputEvent);
        _previous = inputEvent;
      }
    }
  }
}