// Author: Eric Haines (Eric5h5)
// SOURCE: http://wiki.unity3d.com/index.php/TextureScale

namespace Mapbox.Examples.Voxels
{
    using System.Threading;
    using UnityEngine;

	public class TextureScale
	{
		public class ThreadData
		{
			public int start;
			public int end;
			public ThreadData(int s, int e)
			{
				start = s;
				end = e;
			}
		}

		private static Color[] texColors;
		private static Color[] newColors;
		private static int w;
		private static float ratioX;
		private static float ratioY;
		private static int w2;
		private static int finishCount;
		private static Mutex mutex;

		public static void Point(Texture2D tex, int newWidth, int newHeight)
		{
			ThreadedScale(tex, newWidth, newHeight, false);
		}

		public static void Bilinear(Texture2D tex, int newWidth, int newHeight)
		{
			ThreadedScale(tex, newWidth, newHeight, true);
		}

		private static void ThreadedScale(Texture2D tex, int newWidth, int newHeight, bool useBilinear)
		{
			texColors = tex.GetPixels();
			newColors = new Color[newWidth * newHeight];
			if (useBilinear)
			{
				ratioX = 1.0f / ((float)newWidth / (tex.width - 1));
				ratioY = 1.0f / ((float)newHeight / (tex.height - 1));
			}
			else {
				ratioX = ((float)tex.width) / newWidth;
				ratioY = ((float)tex.height) / newHeight;
			}
			w = tex.width;
			w2 = newWidth;
#if WINDOWS_UWP
			var cores = 1;
#else
			var cores = Mathf.Min(SystemInfo.processorCount, newHeight);
#endif
			var slice = newHeight / cores;

			finishCount = 0;
			if (mutex == null)
			{
				mutex = new Mutex(false);
			}

#if WINDOWS_UWP
				ThreadData threadData = new ThreadData(0, newHeight);
				if (useBilinear)
				{
					BilinearScale(threadData);
				}
				else
				{
					PointScale(threadData);
				}
#else
			if (cores > 1)
			{
				int i = 0;
				ThreadData threadData;
				for (i = 0; i < cores - 1; i++)
				{
					threadData = new ThreadData(slice * i, slice * (i + 1));
					ParameterizedThreadStart ts = useBilinear ? new ParameterizedThreadStart(BilinearScale) : new ParameterizedThreadStart(PointScale);
					Thread thread = new Thread(ts);
					thread.Start(threadData);
				}
				threadData = new ThreadData(slice * i, newHeight);
				if (useBilinear)
				{
					BilinearScale(threadData);
				}
				else
				{
					PointScale(threadData);
				}
				while (finishCount < cores)
				{
					Thread.Sleep(1);
				}
			}
			else
			{
				ThreadData threadData = new ThreadData(0, newHeight);
				if (useBilinear)
				{
					BilinearScale(threadData);
				}
				else
				{
					PointScale(threadData);
				}
			}
#endif

			tex.Resize(newWidth, newHeight);
			tex.SetPixels(newColors);
			tex.Apply();

			texColors = null;
			newColors = null;
		}

		public static void BilinearScale(System.Object obj)
		{
			ThreadData threadData = (ThreadData)obj;
			for (var y = threadData.start; y < threadData.end; y++)
			{
				int yFloor = (int)Mathf.Floor(y * ratioY);
				var y1 = yFloor * w;
				var y2 = (yFloor + 1) * w;
				var yw = y * w2;

				for (var x = 0; x < w2; x++)
				{
					int xFloor = (int)Mathf.Floor(x * ratioX);
					var xLerp = x * ratioX - xFloor;
					newColors[yw + x] = ColorLerpUnclamped(ColorLerpUnclamped(texColors[y1 + xFloor], texColors[y1 + xFloor + 1], xLerp),
														   ColorLerpUnclamped(texColors[y2 + xFloor], texColors[y2 + xFloor + 1], xLerp),
														   y * ratioY - yFloor);
				}
			}

			mutex.WaitOne();
			finishCount++;
			mutex.ReleaseMutex();
		}

		public static void PointScale(System.Object obj)
		{
			ThreadData threadData = (ThreadData)obj;
			for (var y = threadData.start; y < threadData.end; y++)
			{
				var thisY = (int)(ratioY * y) * w;
				var yw = y * w2;
				for (var x = 0; x < w2; x++)
				{
					newColors[yw + x] = texColors[(int)(thisY + ratioX * x)];
				}
			}

			mutex.WaitOne();
			finishCount++;
			mutex.ReleaseMutex();
		}

		private static Color ColorLerpUnclamped(Color c1, Color c2, float value)
		{
			return new Color(c1.r + (c2.r - c1.r) * value,
						  c1.g + (c2.g - c1.g) * value,
						  c1.b + (c2.b - c1.b) * value,
						  c1.a + (c2.a - c1.a) * value);
		}
	}
}