// 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.Threading;

namespace System.Reactive.Disposables
{
    /// <summary>
    /// Provides a set of static methods for creating <see cref="IDisposable"/> objects.
    /// </summary>
    public static partial class Disposable
    {
        /// <summary>
        /// Represents a disposable that does nothing on disposal.
        /// </summary>
        private sealed class EmptyDisposable : IDisposable
        {
            /// <summary>
            /// Singleton default disposable.
            /// </summary>
            public static readonly EmptyDisposable Instance = new();

            private EmptyDisposable()
            {
            }

            /// <summary>
            /// Does nothing.
            /// </summary>
            public void Dispose()
            {
                // no op
            }
        }

        /// <summary>
        /// Gets the disposable that does nothing when disposed.
        /// </summary>
        public static IDisposable Empty => EmptyDisposable.Instance;

        /// <summary>
        /// Creates a disposable object that invokes the specified action when disposed.
        /// </summary>
        /// <param name="dispose">Action to run during the first call to <see cref="IDisposable.Dispose"/>. The action is guaranteed to be run at most once.</param>
        /// <returns>The disposable object that runs the given action upon disposal.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="dispose"/> is <c>null</c>.</exception>
        public static IDisposable Create(Action dispose)
        {
            if (dispose == null)
            {
                throw new ArgumentNullException(nameof(dispose));
            }

            return new AnonymousDisposable(dispose);
        }

        /// <summary>
        /// Creates a disposable object that invokes the specified action when disposed.
        /// </summary>
        /// <param name="state">The state to be passed to the action.</param>
        /// <param name="dispose">Action to run during the first call to <see cref="IDisposable.Dispose"/>. The action is guaranteed to be run at most once.</param>
        /// <returns>The disposable object that runs the given action upon disposal.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="dispose"/> is <c>null</c>.</exception>
        public static IDisposable Create<TState>(TState state, Action<TState> dispose)
        {
            if (dispose == null)
            {
                throw new ArgumentNullException(nameof(dispose));
            }

            return new AnonymousDisposable<TState>(state, dispose);
        }
    }
}