// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT License.
// See the LICENSE file in the project root for more information. 

using System.Reactive.Concurrency;
using System.Threading;

namespace System.Reactive.Disposables
{
    /// <summary>
    /// Represents a disposable resource whose disposal invocation will be posted to the specified <seealso cref="SynchronizationContext"/>.
    /// </summary>
    public sealed class ContextDisposable : ICancelable
    {
        private volatile IDisposable _disposable;

        /// <summary>
        /// Initializes a new instance of the <see cref="ContextDisposable"/> class that uses the specified <see cref="SynchronizationContext"/> on which to dispose the specified disposable resource.
        /// </summary>
        /// <param name="context">Context to perform disposal on.</param>
        /// <param name="disposable">Disposable whose Dispose operation to run on the given synchronization context.</param>
        /// <exception cref="ArgumentNullException"><paramref name="context"/> or <paramref name="disposable"/> is null.</exception>
        public ContextDisposable(SynchronizationContext context, IDisposable disposable)
        {
            Context = context ?? throw new ArgumentNullException(nameof(context));
            _disposable = disposable ?? throw new ArgumentNullException(nameof(disposable));
        }

        /// <summary>
        /// Gets the provided <see cref="SynchronizationContext"/>.
        /// </summary>
        public SynchronizationContext Context { get; }

        /// <summary>
        /// Gets a value that indicates whether the object is disposed.
        /// </summary>
        public bool IsDisposed => _disposable == BooleanDisposable.True;

        /// <summary>
        /// Disposes the underlying disposable on the provided <see cref="SynchronizationContext"/>.
        /// </summary>
        public void Dispose()
        {
            var old = Interlocked.Exchange(ref _disposable, BooleanDisposable.True);

            if (old != BooleanDisposable.True)
            {
                Context.PostWithStartComplete(static d => d.Dispose(), old);
            }
        }
    }
}