// 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.

namespace System.Threading.Tasks
{
    /// <summary>Provides a set of static methods for working with specific kinds of <see cref="Task"/> instances.</summary>
    public static class TaskExtensions
    {
        /// <summary>Creates a proxy <see cref="Task"/> that represents the asynchronous operation of a <see cref="Task{Task}"/>.</summary>
        /// <param name="task">The <see cref="Task{Task}"/> to unwrap.</param>
        /// <returns>A <see cref="Task"/> that represents the asynchronous operation of the provided <see cref="Task{Task}"/>.</returns>
        public static Task Unwrap(this Task<Task> task)
        {
            if (task == null)
            {
                throw new ArgumentNullException(nameof(task));
            }

            // If the task hasn't completed or was faulted/canceled, wrap it in an unwrap promise. Otherwise,
            // it completed successfully.  Return its inner task to avoid unnecessary wrapping, or if the inner
            // task is null, return a canceled task to match the same semantics as CreateUnwrapPromise.
            return
                !task.IsCompletedSuccessfully ? Task.CreateUnwrapPromise<VoidTaskResult>(task, lookForOce: false) :
                task.Result ??
                Task.FromCanceled(new CancellationToken(true));
        }

        /// <summary>Creates a proxy <see cref="Task{TResult}"/> that represents the asynchronous operation of a <see cref="Task{Task{TResult}}"/>.</summary>
        /// <param name="task">The <see cref="Task{Task{TResult}}"/> to unwrap.</param>
        /// <returns>A <see cref="Task{TResult}"/> that represents the asynchronous operation of the provided <see cref="Task{Task{TResult}}"/>.</returns>
        public static Task<TResult> Unwrap<TResult>(this Task<Task<TResult>> task)
        {
            if (task == null)
            {
                throw new ArgumentNullException(nameof(task));
            }

            // If the task hasn't completed or was faulted/canceled, wrap it in an unwrap promise. Otherwise,
            // it completed successfully.  Return its inner task to avoid unnecessary wrapping, or if the inner
            // task is null, return a canceled task to match the same semantics as CreateUnwrapPromise.
            return
                !task.IsCompletedSuccessfully ? Task.CreateUnwrapPromise<TResult>(task, lookForOce: false) :
                task.Result ??
                Task.FromCanceled<TResult>(new CancellationToken(true));
        }
    }
}
