using System;

namespace Utility
{
	/// <summary>
	/// An object that invokes an action after an amount of time has elapsed and
	/// optionally continues repeating until told to stop.
	/// </summary>
	public sealed class Timer
	{
		private static readonly Pool<Timer> timers = new Pool<Timer>(10, t => t.valid)
 		{
 			// Initialize is invoked whenever we get an instance through New()
 			Initialize = t => 
			{
				t.valid = true;
				t.time = 0f;
			},

 			// Deinitialize is invoked whenever an object is reclaimed during CleanUp()
 			Deinitialize = t =>
			{
				t.tick = null;
				t.Tag = null;
			}
 		};

		private bool valid;
		private float time;
		private float tickLength;
		private bool repeats;
		private Action<Timer> tick;

		/// <summary>
		/// Gets or sets some extra data to the timer.
		/// </summary>
		public object Tag { get; set; }

		/// <summary>
		/// Gets whether or not this timer repeats.
		/// </summary>
		public bool Repeats { get { return repeats; } }

		/// <summary>
		/// Gets the length of time (in seconds) between ticks of the timer.
		/// </summary>
		public float TickLength { get { return tickLength; } }

		/// <summary>
		/// Creates a new Timer.
		/// </summary>
		/// <param name="tickLength">The amount of time between the timer's ticks.</param>
		/// <param name="repeats">Whether or not the timer repeats.</param>
		/// <param name="tick">An action to perform when the timer ticks.</param>
		/// <returns>The new Timer object or null if the timer pool is full.</returns>
		public static Timer Create(float tickLength, bool repeats, Action<Timer> tick)
		{
			if (tickLength <= 0f)
				throw new ArgumentException("tickLength must be greater than zero.");
			if (tick == null)
				throw new ArgumentNullException("tick");

			// get a new timer from the pool
			Timer t = timers.New();
			t.tickLength = tickLength;
			t.repeats = repeats;
			t.tick = tick;

			return t;
		}

		/// <summary>
		/// Stops the timer.
		/// </summary>
		public void Stop()
		{
			valid = false;
		}

		/// <summary>
		/// Updates all the Timers.
		/// </summary>
		/// <param name="dt">The elapsed time (in seconds) to advance the timers. Generally you want to pass in (float)gameTime.ElapsedGameTime.TotalSeconds from your main Game class.</param>
		public static void Update(float dt)
		{
			for (int i = 0; i < timers.ValidCount; i++)
			{
				Timer t = timers[i];

				// if a timer is stopped manually, it may not
				// be valid at this point so we skip it.
				if (!t.valid)
					continue;

				// update the timer's time
				t.time += dt;

				// if the timer passed its tick length...
				if (t.time >= t.tickLength)
				{
					// perform the action
					t.tick(t);

					// subtract the tick length in case we need to repeat
					t.time -= t.tickLength;

					// if the timer doesn't repeat, it is no longer valid
					if (!t.repeats)
						t.valid = false;
				}
			}

			// clean up any invalid timers
			timers.CleanUp();
		}
	}
}