import 'dart:async';
import 'dart:collection';
import 'dart:ui';

/// A simple Mutex implementation using a [Completer].
class Mutex {
  final _completerQueue = Queue<Completer<void>>();

  /// Runs the given [run] function-block in a thread-safe/blocked zone. A convenient `unlock()`
  /// is provided, which can be called anywhere to signal re-entry.
  FutureOr<T> lockAndRun<T>({
    required FutureOr<T> Function(VoidCallback unlock) run,
  }) async {
    final completer = Completer<void>();
    _completerQueue.add(completer);
    if (_completerQueue.first != completer) {
      await _completerQueue.removeFirst().future;
    }
    final value = await run(completer.complete);
    return value;
  }

  /// Allows listening to the completion status of the last worker process to be released.
  Future<void> get lastOperationCompletionAwaiter =>
      _completerQueue.isNotEmpty ? _completerQueue.last.future : Future.value();
}