// Copyright (c) 2015, 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 'digest.dart';

/// A sink used to get a digest value out of `Hash.startChunkedConversion`.
class DigestSink implements Sink<Digest> {
  /// The value added to the sink.
  ///
  /// A value must have been added using [add] before reading the `value`.
  Digest get value => _value!;

  Digest? _value;

  /// Adds [value] to the sink.
  ///
  /// Unlike most sinks, this may only be called once.
  @override
  void add(Digest value) {
    if (_value != null) throw StateError('add may only be called once.');
    _value = value;
  }

  @override
  void close() {
    if (_value == null) throw StateError('add must be called once.');
  }
}