using System;
using UnityEngine;
using System.Threading.Tasks;
using System.Collections;
using System.Collections.Generic;

namespace UnityAsync
{
	/// <summary>
	/// Encapsulates a <see cref="System.Threading.Tasks.Task"/>, allowing it to be yielded in an IEnumerator coroutine.
	/// </summary>
	public class TaskYieldInstruction : CustomYieldInstruction
	{
		readonly Task task;

		public TaskYieldInstruction(Task task) => this.task = task;

		public override bool keepWaiting => !task.IsCompleted;
	}

	/// <summary>
	/// Encapsulates a <see cref="System.Threading.Tasks.Task{TResult}"/>, allowing it to be yielded in an IEnumerator coroutine.
	/// </summary>
	public class TaskYieldInstruction<TResult> : IEnumerator<TResult>
	{
		readonly Task<TResult> task;

		public TaskYieldInstruction(Task<TResult> task) => this.task = task;

		object IEnumerator.Current => Current;
		
		/// <summary>
		/// Returns the encapsulated <see cref="System.Threading.Tasks.Task{TResult}"/>'s result if it has completed, otherwise the
		/// default TResult value.
		/// </summary>
		public TResult Current => task.IsCompleted ? task.Result : default;

		public void Dispose() => task.Dispose();
		public bool MoveNext() => !task.IsCompleted;
		public void Reset() => throw new NotSupportedException();
	}
}