using UnityEngine;
using System.Collections;
using UnityEngine.Rendering;
using System.Collections.Generic;
using System;

namespace UnityEngine.ScriptableRenderLoop
{
	[System.Serializable]
	public struct ShadowSettings
	{
		public bool 	enabled;
		public int 		shadowAtlasWidth;
		public int 		shadowAtlasHeight;

		public float   	maxShadowDistance;
		public int 		directionalLightCascadeCount;
		public Vector3 	directionalLightCascades;


		public static ShadowSettings Default
		{
			get
			{
				ShadowSettings settings;
				settings.enabled = true;
				settings.shadowAtlasHeight = settings.shadowAtlasWidth = 4096;
				settings.directionalLightCascadeCount = 1;
				settings.directionalLightCascades = new Vector3 (0.05F, 0.2F, 0.3F);
				settings.directionalLightCascadeCount = 4;
				settings.maxShadowDistance = 1000.0F;
				return settings;
			}
		}
	}

	public struct InputShadowLightData
	{
		public int  		lightIndex;
		public int 			shadowResolution;
	}

	public struct ShadowLight
	{
		public int shadowSliceIndex;
		public int shadowSliceCount;
	}

	public struct ShadowSliceData
	{
		public Matrix4x4 	shadowTransform;
		public int 			atlasX;
		public int 			atlasY;
		public int 			shadowResolution;
	}

	public struct ShadowOutput
	{
		public ShadowSliceData[] 	shadowSlices;
		public ShadowLight[]     	shadowLights;
		public Vector4[] 			directionalShadowSplitSphereSqr;

		public int GetShadowSliceCountLightIndex(int lightIndex)
		{
			return shadowLights[lightIndex].shadowSliceCount;
		}

		public int GetShadowSliceIndex(int lightIndex, int sliceIndex)
		{
			if (sliceIndex >= shadowLights[lightIndex].shadowSliceCount)
				throw new System.IndexOutOfRangeException ();
			
			return shadowLights[lightIndex].shadowSliceIndex + sliceIndex;
		}
	}
		
	public struct ShadowRenderPass : IDisposable
	{
		ShadowSettings 				m_Settings;

		[NonSerialized]
		bool 						m_bFailedToPackLastTime;
		int 						m_ShadowTexName;
		const int 					kDepthBuffer = 24;


		public ShadowRenderPass(ShadowSettings settings)
		{
			m_Settings = settings;
			m_bFailedToPackLastTime = false;
			m_ShadowTexName = Shader.PropertyToID("g_tShadowBuffer");
		}

		public void Dispose()
		{
			
		}

		struct AtlasEntry
		{
			public AtlasEntry(int splitIndex, int lightIndex)
			{
				this.splitIndex = splitIndex;
				this.lightIndex = lightIndex;
			}

			public int splitIndex;
			public int lightIndex;
		}

		int CalculateNumShadowSplits(int index, ActiveLight[] lights)
		{
			LightType lightType = lights [index].lightType;
			if (lightType == LightType.Spot)
				return 1;

			if (lightType == LightType.Directional)
				return m_Settings.directionalLightCascadeCount;

			return 6;
		}

		static public void ClearPackedShadows(ActiveLight[] lights, out ShadowOutput packedShadows)
		{
			packedShadows.directionalShadowSplitSphereSqr = null;
			packedShadows.shadowSlices = null;
			packedShadows.shadowLights = new ShadowLight[lights.Length];
		}

		//---------------------------------------------------------------------------------------------------------------------------------------------------
		bool AutoPackLightsIntoShadowTexture(List<InputShadowLightData> shadowLights, ActiveLight[] lights, out ShadowOutput packedShadows)
		{
			List<int> shadowIndices = new List<int>();

			//@TODO: Disallow multiple directional lights

			for (int i = 0; i < shadowLights.Count; i++)
			{
				shadowIndices.Add (shadowLights[i].lightIndex);
			}

			// World's stupidest sheet packer:
			//    1. Sort all lights from largest to smallest
			//    2. In a left->right, top->bottom pattern, fill quads until you reach the edge of the texture
			//    3. Move position to x=0, y=bottomOfFirstTextureInThisRow
			//    4. Goto 2.
			// Yes, this will produce holes as the quads shrink, but it's good enough for now. I'll work on this more later to fill the gaps.

			// Sort all lights from largest to smallest
			shadowIndices.Sort(
				delegate( int l1, int l2 )
				{
					int nCompare = 0;
					// Sort shadow-casting lights by shadow resolution
					nCompare = shadowLights[l1].shadowResolution.CompareTo(shadowLights[l2].shadowResolution); // Sort by shadow size

					if ( nCompare == 0 ) // Same, so sort by range to stabilize sort results
						nCompare = lights[l1].range.CompareTo( lights[l2].range ); // Sort by shadow size

					if ( nCompare == 0 ) // Still same, so sort by instance ID to stabilize sort results
						nCompare = lights[l1].light.GetInstanceID().CompareTo( lights[l2].light.GetInstanceID() );

					return nCompare;
				}
			);
				
			// Start filling lights into texture
			List<AtlasEntry> requestedPages = new List<AtlasEntry>();
			packedShadows.shadowLights = new ShadowLight[lights.Length];
			for (int i = 0; i != shadowIndices.Count;i++)
			{
				int numShadowSplits = CalculateNumShadowSplits(shadowIndices[i], lights);

				packedShadows.shadowLights[shadowIndices [i]].shadowSliceCount = numShadowSplits;
				packedShadows.shadowLights[shadowIndices [i]].shadowSliceIndex = requestedPages.Count;

				for (int s = 0; s < numShadowSplits; s++)
					requestedPages.Add (new AtlasEntry (requestedPages.Count, shadowIndices[i]));
			}

			int nCurrentX = 0;
			int nCurrentY = -1;
			int nNextY = 0;

			packedShadows.shadowSlices = new ShadowSliceData[requestedPages.Count];
			packedShadows.directionalShadowSplitSphereSqr = new Vector4[4];

			foreach (AtlasEntry entry in requestedPages)
			{
				int shadowResolution = shadowLights[entry.lightIndex].shadowResolution;

				// Check if first texture is too wide
				if ( nCurrentY == -1 )
				{
					if ( ( shadowResolution > m_Settings.shadowAtlasWidth ) || ( shadowResolution > m_Settings.shadowAtlasHeight ) )
					{
						Debug.LogError( "ERROR! Shadow packer ran out of space in the " + m_Settings.shadowAtlasWidth + "x" + m_Settings.shadowAtlasHeight + " texture!\n\n" );
						m_bFailedToPackLastTime = true;
						ClearPackedShadows (lights, out packedShadows);
						return false;
					}
				}

				// Goto next scanline
				if ( ( nCurrentY == -1 ) || ( ( nCurrentX + shadowResolution ) > m_Settings.shadowAtlasWidth ) )
				{
					nCurrentX = 0;
					nCurrentY = nNextY;
					nNextY += shadowResolution;
				}

				// Check if we've run out of space
				if ( ( nCurrentY + shadowResolution ) > m_Settings.shadowAtlasHeight )
				{
					Debug.LogError( "ERROR! Shadow packer ran out of space in the " + m_Settings.shadowAtlasWidth + "x" + m_Settings.shadowAtlasHeight + " texture!\n\n" );
					m_bFailedToPackLastTime = true;
					ClearPackedShadows (lights, out packedShadows);
					return false;
				}

				// Save location to light
				packedShadows.shadowSlices[entry.splitIndex].atlasX = nCurrentX;
				packedShadows.shadowSlices[entry.splitIndex].atlasY = nCurrentY;
				packedShadows.shadowSlices[entry.splitIndex].shadowResolution = shadowResolution;

				// Move ahead
				nCurrentX += shadowResolution;

				//Debug.Log( "Sheet packer: " + vl.m_cachedLight.name + " ( " + vl.m_shadowX + ", " + vl.m_shadowY + " ) " + vl.m_shadowResolution + "\n\n" );
			}

			if ( m_bFailedToPackLastTime )
			{
				m_bFailedToPackLastTime = false;
				Debug.Log( "SUCCESS! Shadow packer can now fit all lights into the " + m_Settings.shadowAtlasWidth + "x" + m_Settings.shadowAtlasHeight + " texture!\n\n" );
			}

			return requestedPages.Count != 0;
		}

		static List<InputShadowLightData> GetInputShadowLightData(CullResults cullResults)
		{
			var shadowCasters = new List<InputShadowLightData> ();
			ActiveLight[] lights = cullResults.culledLights;
			int directionalLightCount = 0;
			for (int i = 0; i < lights.Length; i++)
			{
				//@TODO: ignore baked. move this logic to c++...
				if (lights[i].light.shadows != LightShadows.None)
				{

					// Only a single directional shadow casting light is supported
					if (lights [i].lightType == LightType.Directional)
					{
						directionalLightCount++;
						if (directionalLightCount != 1)
							continue;
					}

					AdditionalLightData additionalLight = lights [i].light.GetComponent<AdditionalLightData> ();

					InputShadowLightData light;
					light.lightIndex = i;
					light.shadowResolution = AdditionalLightData.GetShadowResolution(additionalLight);

					shadowCasters.Add (light);
				}
			}
			return shadowCasters;
		}

		public void UpdateCullingParameters(ref CullingParameters parameters)
		{
			parameters.shadowDistance = Mathf.Min (m_Settings.maxShadowDistance, parameters.shadowDistance);
		}

		public void Render(RenderLoop loop, CullResults cullResults, out ShadowOutput packedShadows)
		{
			if (!m_Settings.enabled)
			{
				ClearPackedShadows(cullResults.culledLights, out packedShadows);
			}

			// Pack all shadow quads into the texture
			if ( !AutoPackLightsIntoShadowTexture(GetInputShadowLightData(cullResults), cullResults.culledLights, out packedShadows) )
			{
				// No shadowing lights found, so skip all rendering
				return;
			}

			RenderPackedShadows (loop, cullResults, ref packedShadows);
		}

		//---------------------------------------------------------------------------------------------------------------------------------------------------
		// Render shadows
		//---------------------------------------------------------------------------------------------------------------------------------------------------
		void RenderPackedShadows(RenderLoop loop, CullResults cullResults, ref ShadowOutput packedShadows)
		{
			var setRenderTargetCommandBuffer = new CommandBuffer ();

			setRenderTargetCommandBuffer.GetTemporaryRT (m_ShadowTexName, m_Settings.shadowAtlasWidth, m_Settings.shadowAtlasHeight, kDepthBuffer, FilterMode.Bilinear, RenderTextureFormat.Shadowmap, RenderTextureReadWrite.Linear);
			setRenderTargetCommandBuffer.SetRenderTarget (new RenderTargetIdentifier (m_ShadowTexName));

			setRenderTargetCommandBuffer.ClearRenderTarget (true, true, Color.green);
			loop.ExecuteCommandBuffer (setRenderTargetCommandBuffer);
			setRenderTargetCommandBuffer.Dispose ();

			ActiveLight[] activeLights = cullResults.culledLights;
			var shadowSlices = packedShadows.shadowSlices;

			// Render each light's shadow buffer into a subrect of the shared depth texture
			for ( int lightIndex = 0; lightIndex < packedShadows.shadowLights.Length; lightIndex++ )
			{
				int shadowSliceCount = packedShadows.shadowLights[lightIndex].shadowSliceCount;
				if (shadowSliceCount == 0)
					continue;
				
				Profiler.BeginSample ("Shadows.GetShadowCasterBounds");
				Bounds bounds;
				if (!cullResults.GetShadowCasterBounds (lightIndex, out bounds))
				{
					Profiler.EndSample ();
					return;
				}
				Profiler.EndSample ();

				Profiler.BeginSample ("Shadows.DrawShadows");

				Matrix4x4 proj;
				Matrix4x4 view;

				LightType lightType = activeLights[lightIndex].lightType;
				Vector3 lightDirection = activeLights[lightIndex].light.transform.forward;
				var shadowNearClip = activeLights[lightIndex].light.shadowNearPlane;

				int shadowSliceIndex = packedShadows.GetShadowSliceIndex (lightIndex, 0);
					
				if (lightType == LightType.Spot)
				{
					DrawShadowsSettings settings = new DrawShadowsSettings(cullResults, lightIndex);
					bool needRendering = cullResults.ComputeSpotShadowsMatricesAndCullingPrimitives(lightIndex, out view, out proj, out settings.splitData);
					SetupShadowSplitMatrices(ref packedShadows.shadowSlices[shadowSliceIndex], proj, view);
					if (needRendering)
						RenderShadowSplit(ref shadowSlices[shadowSliceIndex], lightDirection, proj, view, ref loop, settings);
				}
				else if (lightType == LightType.Directional)
				{
					Vector3 splitRatio = m_Settings.directionalLightCascades;

					for (int s = 0; s < 4; ++s)
						packedShadows.directionalShadowSplitSphereSqr[s] = new Vector4 (0, 0, 0, float.NegativeInfinity);

					for (int s = 0; s < shadowSliceCount; ++s, shadowSliceIndex++)
					{
						var settings = new DrawShadowsSettings(cullResults, lightIndex);
						var shadowResolution = shadowSlices [shadowSliceIndex].shadowResolution;
						bool needRendering = cullResults.ComputeDirectionalShadowMatricesAndCullingPrimitives(lightIndex, s, shadowSliceCount, splitRatio, shadowResolution, shadowNearClip, out view, out proj, out settings.splitData);

						packedShadows.directionalShadowSplitSphereSqr[s] = settings.splitData.cullingSphere;
						packedShadows.directionalShadowSplitSphereSqr[s].w *= packedShadows.directionalShadowSplitSphereSqr[s].w;

						SetupShadowSplitMatrices(ref shadowSlices[shadowSliceIndex], proj, view);
						if (needRendering)
							RenderShadowSplit(ref shadowSlices[shadowSliceIndex], lightDirection, proj, view, ref loop, settings);
					}
				}
				else if (lightType == LightType.Point)
				{
					for(int s = 0; s < shadowSliceCount; ++s, shadowSliceIndex++)
					{
						DrawShadowsSettings settings = new DrawShadowsSettings(cullResults, lightIndex);
						bool needRendering = cullResults.ComputePointShadowsMatricesAndCullingPrimitives(lightIndex, (CubemapFace)s, 2.0f, out view, out proj, out settings.splitData);

						SetupShadowSplitMatrices(ref shadowSlices[shadowSliceIndex], proj, view);
						if (needRendering)
							RenderShadowSplit(ref shadowSlices[shadowSliceIndex], lightDirection, proj, view, ref loop, settings);
					}
				}
				Profiler.EndSample ();
			}
		}


		private void SetupShadowSplitMatrices(ref ShadowSliceData lightData, Matrix4x4 proj, Matrix4x4 view)
		{
			Matrix4x4 matScaleBias = Matrix4x4.identity;
			matScaleBias.m00 = 0.5f;
			matScaleBias.m11 = 0.5f;
			matScaleBias.m22 = 0.5f;
			matScaleBias.m03 = 0.5f;
			matScaleBias.m13 = 0.5f;
			matScaleBias.m23 = 0.5f;

			Matrix4x4 matTile = Matrix4x4.identity;
			matTile.m00 = (float)lightData.shadowResolution / (float)m_Settings.shadowAtlasWidth;
			matTile.m11 = (float)lightData.shadowResolution / (float)m_Settings.shadowAtlasHeight;
			matTile.m03 = (float)lightData.atlasX / (float)m_Settings.shadowAtlasWidth;
			matTile.m13 = (float)lightData.atlasY / (float)m_Settings.shadowAtlasHeight;
			lightData.shadowTransform = matTile * matScaleBias * proj * view;
		}

		//---------------------------------------------------------------------------------------------------------------------------------------------------	
		private void RenderShadowSplit(ref ShadowSliceData slice, Vector3 lightDirection, Matrix4x4 proj, Matrix4x4 view, ref RenderLoop loop, DrawShadowsSettings settings)
		{
			var commandBuffer = new CommandBuffer();
			commandBuffer.name = "ShadowSetup";

			// Set viewport / matrices etc
			commandBuffer.SetViewport(new Rect(slice.atlasX, slice.atlasY, slice.shadowResolution, slice.shadowResolution));
			//commandBuffer.ClearRenderTarget (true, true, Color.green);
			commandBuffer.SetGlobalVector("g_vLightDirWs", new Vector4(lightDirection.x, lightDirection.y, lightDirection.z));
			commandBuffer.SetProjectionAndViewMatrices(proj, view);
			//	commandBuffer.SetGlobalDepthBias (1.0F, 1.0F);
			loop.ExecuteCommandBuffer(commandBuffer);
			commandBuffer.Dispose();

			// Render
			loop.DrawShadows(ref settings);
		}
	}
}