// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See LICENSE in the project root for license information.

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;

namespace HoloToolkit.Unity
{
	/// <summary>
	/// Encapsulates access to GPU timing methods.
	/// </summary>
	public static class GpuTiming
	{
		[DllImport("GpuTiming")]
		private static extern IntPtr GetRenderEventFunc();

		[DllImport("GpuTiming")]
		private static extern double GetLastFrameGPUTime(int eventId);

		private const int BaseBeginEventId = 1000;
		private const int BaseEndEventId = 2000;

		private static int nextAvailableEventId = 0;
		private static Stack<int> currentEventId = new Stack<int>();
		private static Dictionary<string, int> eventIds = new Dictionary<string, int>();
		/// <summary>
		/// Gets the latest available sample time for the given event. 
		/// </summary>
		/// <param name="eventId">Name of the event.</param>
		/// <returns>Time in milliseconds.</returns>
		public static double GetTime(string eventId)
		{
			int eventValue;
			if (eventIds.TryGetValue(eventId, out eventValue))
			{
				return GetLastFrameGPUTime(eventValue);
			}

			return -1;
		}
		/// <summary>
		/// Begins sampling GPU time. 
		/// </summary>
		/// <param name="eventId">Name of the event.</param>
		/// <returns>Returns true if a BeginSample with the same event name was last added.</returns>
		public static bool BeginSample(string eventId)
		{
			int eventValue;
			if (!eventIds.TryGetValue(eventId, out eventValue))
			{
				if (nextAvailableEventId == BaseEndEventId)
				{
					return false;
				}

				eventValue = nextAvailableEventId;
				eventIds.Add(eventId, nextAvailableEventId++);
			}

			if (currentEventId.Contains(eventValue))
			{
				Debug.LogWarning("BeginSample() is being called without a corresponding EndSample() call.");
				return false;
			}

			currentEventId.Push(eventValue);

			// Begin measuring GPU time
			int eventFunctionId = eventValue + BaseBeginEventId;
			GL.IssuePluginEvent(GetRenderEventFunc(), eventFunctionId);
			return true;
		}
		/// <summary>
		/// Ends the GPU sample currently in flight. 
		/// </summary>
		public static void EndSample()
		{
			if (currentEventId.Count > 0)
			{
				// End measuring GPU frame time
				int eventId = currentEventId.Pop() + BaseEndEventId;
				GL.IssuePluginEvent(GetRenderEventFunc(), eventId);
			}
		}
	}
}
