/// TaskManager.cs
///
/// This is a convenient coroutine API for Unity.
///
/// Example usage:
///   IEnumerator MyAwesomeTask()
///   {
///       while(true) {
///           // ...
///           yield return null;
////      }
///   }
///
///   IEnumerator TaskKiller(float delay, Task t)
///   {
///       yield return new WaitForSeconds(delay);
///       t.Stop();
///   }
///
///   // From anywhere
///   Task my_task = new Task(MyAwesomeTask());
///   new Task(TaskKiller(5, my_task));
///
/// The code above will schedule MyAwesomeTask() and keep it running
/// concurrently until either it terminates on its own, or 5 seconds elapses
/// and triggers the TaskKiller Task that was created.
///
/// Note that to facilitate this API's behavior, a "TaskManager" GameObject is
/// created lazily on first use of the Task API and placed in the scene root
/// with the internal TaskManager component attached. All coroutine dispatch
/// for Tasks is done through this component.

using UnityEngine;
using System.Collections;

/// A Task object represents a coroutine.  Tasks can be started, paused, and stopped.
/// It is an error to attempt to start a task that has been stopped or which has
/// naturally terminated.
public class Task
{
	/// Returns true if and only if the coroutine is running.  Paused tasks
	/// are considered to be running.
	public bool Running {
		get {
			return task.Running;
		}
	}
	
	/// Returns true if and only if the coroutine is currently paused.
	public bool Paused {
		get {
			return task.Paused;
		}
	}
	
	/// Delegate for termination subscribers.  manual is true if and only if
	/// the coroutine was stopped with an explicit call to Stop().
	public delegate void FinishedHandler(bool manual);
	
	/// Termination event.  Triggered when the coroutine completes execution.
	public event FinishedHandler Finished;

	/// Creates a new Task object for the given coroutine.
	///
	/// If autoStart is true (default) the task is automatically started
	/// upon construction.
	public Task(IEnumerator c, bool autoStart = true)
	{
		task = TaskManager.CreateTask(c);
		task.Finished += TaskFinished;
		if(autoStart)
			Start();
	}
	
	/// Begins execution of the coroutine
	public void Start()
	{
		task.Start();
	}

	/// Discontinues execution of the coroutine at its next yield.
	public void Stop()
	{
		task.Stop();
	}
	
	public void Pause()
	{
		task.Pause();
	}
	
	public void Unpause()
	{
		task.Unpause();
	}
	
	void TaskFinished(bool manual)
	{
		FinishedHandler handler = Finished;
		if(handler != null)
			handler(manual);
	}
	
	TaskManager.TaskState task;
}

class TaskManager : MonoBehaviour
{
	public class TaskState
	{
		public bool Running {
			get {
				return running;
			}
		}

		public bool Paused  {
			get {
				return paused;
			}
		}

		public delegate void FinishedHandler(bool manual);
		public event FinishedHandler Finished;

		IEnumerator coroutine;
		bool running;
		bool paused;
		bool stopped;
		
		public TaskState(IEnumerator c)
		{
			coroutine = c;
		}
		
		public void Pause()
		{
			paused = true;
		}
		
		public void Unpause()
		{
			paused = false;
		}
		
		public void Start()
		{
			running = true;
			singleton.StartCoroutine(CallWrapper());
		}
		
		public void Stop()
		{
			stopped = true;
			running = false;
		}
		
		IEnumerator CallWrapper()
		{
			yield return null;
			IEnumerator e = coroutine;
			while(running) {
				if(paused)
					yield return null;
				else {
					if(e != null && e.MoveNext()) {
						yield return e.Current;
					}
					else {
						running = false;
					}
				}
			}
			
			FinishedHandler handler = Finished;
			if(handler != null)
				handler(stopped);
		}
	}

	static TaskManager singleton;

	public static TaskState CreateTask(IEnumerator coroutine)
	{
		if(singleton == null) {
			GameObject go = new GameObject("TaskManager");
			singleton = go.AddComponent<TaskManager>();
		}
		return new TaskState(coroutine);
	}
}