using Delta.Engine.Dynamic;

using Delta.Utilities;



namespace Delta.Engine.Game

{

	/// <summary>

	/// Game Time is used for having a pausable and resetable time source,

	/// which is useful for games that can pause.<para />

	/// Dependant systems are Effects, Physics.

	/// </summary>

	public class GameTime : DynamicModule

	{

		#region CheckEvery (Static)

		/// <summary>

		/// Check every time (e.g. one second, half a second, every 10 seconds)

		/// if the time has passed and return true once in that time frame and

		/// false otherwise. Used for spawning stuff, e.g. every 0.5 seconds and

		/// is very useful to write framerate independent code.

		/// Note: If using a small value here like 1.0f/100.0f and we have less

		/// fps (e.g. 60), then this will return true every time, but obviously

		/// we cannot return true 100 times if this method is only called 60 times.

		/// </summary>

		/// <param name="timeStep">Time step in seconds</param>

		/// <returns>

		/// True if the timeStep is reached, false if we have too many frames and

		/// need to wait until timeStep is reached next.

		/// </returns>

		public static bool CheckEvery(float timeStep)

		{

			// Make sure the timeStep value is valid!

			if (timeStep <= 0)

			{

				Log.Warning("Invalid time step=" + timeStep);

				return true;

			}

			// Calculate with millisecond values calculated in the timer.

			return (int)(Milliseconds / (1000 * timeStep)) >

						 (int)(LastMilliseconds / (1000 * timeStep));

		}



		/// <summary>

		/// Check every time (e.g. one second, half a second, every 10 seconds)

		/// if the time has passed and return true once in that time frame and

		/// false otherwise. Used for spawning stuff, e.g. every 0.5 seconds and

		/// is very useful to write framerate independent code.

		/// Note: If using a small value here like 1.0f/100.0f and we have less

		/// fps (e.g. 60), then this will return true every time, but obviously

		/// we cannot return true 100 times if this method is only called 60 times.

		/// </summary>

		/// <param name="timeStep">Time step in seconds</param>

		/// <param name="startTimeMs">

		/// Only start checking when this time is reached and then every time step

		/// after (in milliseconds).

		/// </param>

		/// <returns>

		/// True if the timeStep is reached, false if we have too many frames and

		/// need to wait until timeStep is reached next.

		/// </returns>

		public static bool CheckEvery(float timeStep, long startTimeMs)

		{

			// Make sure the timeStep value is valid!

			if (startTimeMs < 0 ||

					timeStep <= 0)

			{

				Log.Warning("Invalid timeStep='" + timeStep +

				            "' or startTimeMs='" + startTimeMs + "'");

				return true;

			}

			// Calculate with millisecond values calculated in the timer.

			long relativeStartMs = Milliseconds - startTimeMs;

			if (relativeStartMs < 0)

			{

				// Not started yet

				return false;

			} // if



			long relativeLastMs = LastMilliseconds - startTimeMs;

			return (int)(relativeStartMs / (1000 * timeStep)) >

						 (int)(relativeLastMs / (1000 * timeStep));

		}

		#endregion



		#region GetDeltaToNow (Static)

		/// <summary>

		/// Get delta to now in seconds as a floating point value.

		/// </summary>

		/// <param name="startTimeInMs">The start time in ms.</param>

		/// <returns>Float Delta to Now</returns>

		public static float GetDeltaToNow(long startTimeInMs)

		{

			return (Milliseconds - startTimeInMs) / 1000.0f;

		}

		#endregion



		#region IsRunning (Static)

		/// <summary>

		/// Flag if the game time is updating or not.

		/// </summary>

		public static bool IsRunning

		{

			get

			{

				return Instance.isRunning;

			}

		}

		#endregion



		#region Milliseconds (Static)

		/// <summary>

		/// The elapsed game time in milliseconds.

		/// </summary>

		public static long Milliseconds

		{

			get

			{

				return Instance.milliseconds;

			}

		}

		#endregion



		#region LastMilliseconds (Static)

		/// <summary>

		/// The elapsed game time in milliseconds from the last frame. This allows

		/// us to do some checks from frame to frame to see if a timeout or

		/// cooldown has been reached. See CheckEvery for a use case.

		/// </summary>

		public static long LastMilliseconds

		{

			get

			{

				return Instance.lastMilliseconds;

			}

		}

		#endregion



		#region Delta (Static)

		/// <summary>

		/// Returns the current delta time. It represents the difference between

		/// the last tick and the current tick in seconds (usually small values).

		/// Used for many calculations and updates to make sure the time goes

		/// on constantly no matter how many frames we have per second.

		/// </summary>

		public static float Delta

		{

			get

			{

				return Instance.delta;

			}

		}

		#endregion



		#region TotalTime (Static)

		/// <summary>

		/// The total time since the game time was started.

		/// </summary>

		public static float TotalTime

		{

			get

			{

				return Instance.totalTime;

			}

		}

		#endregion



		#region Paused (event)

		/// <summary>

		/// Event which will occur everytime the game time is paused.

		/// </summary>

		public static event RunDelegate Paused;

		#endregion



		#region Resumed (event)

		/// <summary>

		/// Event which will occur everytime the game time is resumed again.

		/// </summary>

		public static event RunDelegate Resumed;

		#endregion



		#region Private



		#region cachedInstance (Private)

		private static GameTime cachedInstance;

		#endregion



		#region Instance (Private)

		private static GameTime Instance

		{

			get

			{

				if (cachedInstance == null)

				{

					cachedInstance = Factory.Create<GameTime>();

				}



				return cachedInstance;

			}

		}

		#endregion



		#region timeMsOffset (Private)

		private long timeMsOffset;

		#endregion



		#region pauseStartOffset (Private)

		private long pauseStartOffset;

		#endregion



		#region isRunning (Private)

		private bool isRunning;

		#endregion



		#region totalTime (Private)

		/// <summary>

		/// The total time since the game time was started.

		/// </summary>

		private float totalTime;

		#endregion



		#region delta (Private)

		/// <summary>

		/// Returns the current delta time.

		/// </summary>

		private float delta;

		#endregion



		#region milliseconds (Private)

		/// <summary>

		/// Milliseconds the game time has been running.

		/// </summary>

		private long milliseconds;

		#endregion



		#region lastMilliseconds

		/// <summary>

		/// Milliseconds from last frame, allows us to do frame by frame checks.

		/// </summary>

		private long lastMilliseconds;

		#endregion



		#region wasRunningBeforeAppPause

		/// <summary>

		/// Flag if the game time was running before it was paused by the

		/// system information event. If we don't save this state we might

		/// start the game time again accidentally in OnAppResume.

		/// </summary>

		private bool wasRunningBeforeAppPause;

		#endregion



		#endregion



		#region Constructors

		/// <summary>

		/// Create a new game time instance, which is started by default, but can

		/// be stopped or restarted by the game if a new level starts.

		/// </summary>

		internal GameTime()

			: base("GameTime", typeof(Time))

		{

			wasRunningBeforeAppPause = false;

			isRunning = true;

			timeMsOffset += Time.Milliseconds - pauseStartOffset;



			Application.Information.OnAppPause += OnAppPause;

			Application.Information.OnAppResume += OnAppResume;

		}



		/// <summary>

		/// Remove OnAppPause and OnAppResume event handlers added in constructor.

		/// </summary>

		~GameTime()

		{

			Application.Information.OnAppPause -= OnAppPause;

			Application.Information.OnAppResume -= OnAppResume;

		}

		#endregion



		#region OnAppPause

		private void OnAppPause()

		{

			wasRunningBeforeAppPause = isRunning;

			Pause();

		}

		#endregion



		#region OnAppResume

		private void OnAppResume()

		{

			if (wasRunningBeforeAppPause)

			{

				Start();

				wasRunningBeforeAppPause = false;

			}

		}

		#endregion



		#region Start (Static)

		/// <summary>

		/// Start or resume the game time updating.

		/// </summary>

		public static void Start()

		{

			if (IsRunning == false)

			{

				Instance.isRunning = true;

				Instance.timeMsOffset += Time.Milliseconds - Instance.pauseStartOffset;



				// Still notfiy the listeners (if required)

				if (Resumed != null &&

					// but only if the time si resumed from a previous pause

					TotalTime > 0.0f)

				{

					Resumed();

				} // if

			}

		}

		#endregion



		#region Pause (Static)

		/// <summary>

		/// Pause the game time updating.

		/// </summary>

		public static void Pause()

		{

			if (IsRunning)

			{

				Instance.isRunning = false;

				Instance.pauseStartOffset = Time.Milliseconds;



				// Still notfiy the listeners (if required)

				if (Paused != null)

				{

					Paused();

				} // if

			}

		}

		#endregion



		#region Reset (Static)

		/// <summary>

		/// Reset the game time.

		/// </summary>

		public static void Reset()

		{

			Instance.totalTime = 0.0f;

		}

		#endregion



		#region Run (Public)

		/// <summary>

		/// Update the game time.

		/// </summary>

		public override void Run()

		{

			if (IsRunning == false)

			{

				delta = 0.0f;

				return;

			}



			lastMilliseconds = milliseconds;

			milliseconds = Time.Milliseconds - timeMsOffset;



			delta = Time.Delta;

			totalTime += Delta;

		}

		#endregion

	}

}