namespace Caliburn.Micro.Core {
    using System;
    using System.Threading.Tasks;

    /// <summary>
    /// A couroutine that encapsulates an <see cref="System.Threading.Tasks.Task"/>.
    /// </summary>
    public class TaskResult : IResult {
        readonly Task innerTask;

        /// <summary>
        /// Initializes a new instance of the <see cref="TaskResult"/> class.
        /// </summary>
        /// <param name="task">The task.</param>
        public TaskResult(Task task) {
            innerTask = task;
        }

        /// <summary>
        /// Executes the result using the specified context.
        /// </summary>
        /// <param name="context">The context.</param>
        public void Execute(CoroutineExecutionContext context) {
            if (innerTask.IsCompleted)
                OnCompleted(innerTask);
            else
                innerTask.ContinueWith(OnCompleted,
                    System.Threading.SynchronizationContext.Current != null
                        ? TaskScheduler.FromCurrentSynchronizationContext()
                        : TaskScheduler.Current);
        }

        /// <summary>
        /// Called when the asynchronous task has completed.
        /// </summary>
        /// <param name="task">The completed task.</param>
        protected virtual void OnCompleted(Task task) {
            Completed(this, new ResultCompletionEventArgs {WasCancelled = task.IsCanceled, Error = task.Exception});
        }

        /// <summary>
        /// Occurs when execution has completed.
        /// </summary>
        public event EventHandler<ResultCompletionEventArgs> Completed = delegate { };
    }

    /// <summary>
    /// A couroutine that encapsulates an <see cref="System.Threading.Tasks.Task&lt;TResult&gt;"/>.
    /// </summary>
    /// <typeparam name="TResult">The type of the result.</typeparam>
    public class TaskResult<TResult> : TaskResult, IResult<TResult> {
        /// <summary>
        /// Initializes a new instance of the <see cref="TaskResult{TResult}"/> class.
        /// </summary>
        /// <param name="task">The task.</param>
        public TaskResult(Task<TResult> task)
            : base(task) {
        }

        /// <summary>
        /// Gets the result of the asynchronous operation.
        /// </summary>
        public TResult Result { get; private set; }

        /// <summary>
        /// Called when the asynchronous task has completed.
        /// </summary>
        /// <param name="task">The completed task.</param>
        protected override void OnCompleted(Task task) {
            if (!task.IsFaulted && !task.IsCanceled)
                Result = ((Task<TResult>) task).Result;

            base.OnCompleted(task);
        }
    }
}