/* This file is part of the Spring engine (GPL v2 or later), see LICENSE.html */

#ifndef _TERRAIN_NODE_H_
#define _TERRAIN_NODE_H_

#include "TerrainVertexBuffer.h"
#include "Map/SM3/Vector3.h"
#include <vector>

class Frustum;
struct Sm3VisibilityNode;

namespace terrain
{
	struct int2 {
		int2(int x, int y) : x(x), y(y) {}
		int2() : x(0), y(0) {}
		int x;
		int y;
	};

	class Camera;
	struct Heightmap;
	struct QuadMap;
	struct IndexTable;
	class QuadRenderData;
	class QuadNormals;
	struct RenderSetupCollection;
	struct IShaderSetup;
	class TerrainTexture;

//-----------------------------------------------------------------------
// Terrain Quadtree Node
//-----------------------------------------------------------------------

	static const int QUAD_W = 16;
	static const int VERTC = QUAD_W + 1;
	static const int MAX_INDICES  = (QUAD_W + 1) * (QUAD_W + 1) * 2 * 3;
	static const int NUM_VERTICES = (QUAD_W + 1) * (QUAD_W + 1);

	const float SquareSize = 8.0f;
	const float VBufMinDetail = 0.25f; ///< at lod < 0.25f, the vertex buffer is deleted

	const float AREA_TEST_RANGE = 0.05f;

	class TQuad
	{
	public:
		TQuad();
		~TQuad();
		bool isLeaf() const { return childs[0] == NULL; }
		// sqStart=start in square coordinates
		// hmStart=start pixel on hm
		void Build(Heightmap* hm, int2 sqStart, int2 hmStart, int2 quadPos, int w, int depth);
		void Draw(IndexTable* indexTable, bool onlyPositions, int lodState);
		bool InFrustum(Frustum* f);
		float CalcLod(const Vector3& campos);
		void CollectNodes(std::vector<TQuad*>& quads);
		void FreeCachedTexture();

		TQuad* FindSmallestContainingQuad2D(const Vector3& pos, float range, int maxlevel);

		int GetVertexSize();

		// Possible objects linked to this quad, for visibility determination
		std::vector<Sm3VisibilityNode*> nodeLinks;

		TQuad* parent;
		TQuad* childs[4];
		Vector3 start, end;  ///< quad node bounding box
		int2 qmPos; ///< Quad map coordinates
		int2 hmPos;
		int2 sqPos; ///< square position (position on highest detail heightmap)
		int depth, width;
		RenderSetupCollection* textureSetup;
		GLuint cacheTexture;
		/**
		 * maximum of the LOD values calculated for each render contexts
		 * used for determining if the QuadRenderData can be marked as free
		 * @see RenderDataManager::FreeUnused
		 */
		float maxLodValue;

		enum DrawState {
			NoDraw, Parent, Queued, Culled
		} drawState;

		QuadNormals* normalData;
		QuadRenderData* renderData;
	};

	/**
	 * Each render context has a QuadRenderInfo for every quad they have to
	 * render.
	 */
	struct QuadRenderInfo
	{
		int lodState;
		TQuad* quad;
	};

	class RenderContext
	{
	public:
		Camera* cam;
		/// contexts like shadow buffers do not need texturing
		bool needsTexturing;
		bool needsNormalMap;

		std::vector<QuadRenderInfo> quads;
	};

	// renderdata for a visible quad
	class QuadRenderData
	{
	public:
		QuadRenderData();
		~QuadRenderData();

		uint GetDataSize();

		// seems silly yeah, but I use it to set breakpoints in
		TQuad* GetQuad() { return quad; }
		void SetQuad(TQuad* q) { quad = q; }

		// renderdata: normalmap + vertex buffer
		// normalmap for detail preservation
		GLuint normalMap;
		uint normalMapW;
		uint normalMapTexWidth;

		VertexBuffer vertexBuffer;
		int vertexSize;

		int index;
		bool used;
	protected:
		TQuad* quad;
	};

	// Manager for QuadRenderData
	class RenderDataManager {
	public:
		RenderDataManager(Heightmap* roothm, QuadMap* rootqm);
		~RenderDataManager();

		void Free(QuadRenderData* qrd);
		void FreeUnused();
		/// allow the list of free renderdata to be maxFreeRD or lower
		void PruneFreeList(int maxFreeRD = 0);

		void InitializeNode(TQuad* q);
		void InitializeNodeNormalMap(TQuad* q, int cfgNormalMapLevel);

		void UpdateRect(int sx, int sy, int w, int h);

		void ClearStat() {
			normalDataAllocates = 0;
			renderDataAllocates = 0;
		}

		int normalDataAllocates; // performance statistic
		int renderDataAllocates;

		int QuadRenderDataCount() { return qrd.size(); }

	protected:
		QuadRenderData* Allocate();

		std::vector<QuadRenderData*> qrd;
		std::vector<QuadRenderData*> freeRD;
		Heightmap* roothm;
		QuadMap* rootQMap;
	};




//-----------------------------------------------------------------------
// Heightmap
//-----------------------------------------------------------------------
	struct Heightmap {
		Heightmap();
		~Heightmap();

		void Alloc(int W, int H);
		void LodScaleDown(Heightmap* dst);
		void FindMinMax(int2 st, int2 size, float& minH, float& maxH);
		Heightmap* CreateLowDetailHM();
		void GenerateNormals();
		void UpdateLowerUnsynced(int sx, int sy, int w, int h);
		/**
		 * @param level > 0 returns a high detail HM
		 *   < 0 returns a lower detail HM
		 */
		const Heightmap* GetLevel(int level);

		float atSynced(int x, int y) const { return dataSynced[y * w + x]; }
		float atUnsynced(int x, int y) const { return dataUnsynced[y * w + x]; }
		const uchar* GetNormal(int x, int y) const { return &normalData[3 * (y * w + x)]; }

		int w, h;
		std::vector<float> dataSynced;
		std::vector<float> dataUnsynced;
		// float scale, offset;
		float squareSize;

		/**
		 * optional heightmap normals, stored as compressed vectors
		 * (3 bytes per normal)
		 */
        uchar* normalData;

		// geo-mip-map chain links
		Heightmap* lowDetail;
		Heightmap* highDetail;
	};

//-----------------------------------------------------------------------
// Quad map - stores a 2D map of the quad nodes, 
//            for quick access of nabours
//-----------------------------------------------------------------------
	struct QuadMap 
	{
		QuadMap()
			: w(0)
			, map(NULL)
			, highDetail(NULL)
			, lowDetail(NULL)
		{
		}
		~QuadMap() {
			delete[] map;
		}

		void Alloc(int W);
		void Fill(TQuad* root);
		TQuad*& At(int x, int y) { return map[y*w + x]; }

		int w;
		TQuad** map;

		QuadMap* highDetail;
		QuadMap* lowDetail;
	};


	/**
	 * Applies a "sobel" filter to the heightmap to find the slope in X
	 * and Z(Y in heightmap) direction.
	 */
	inline void CalculateTangents(const Heightmap* hm, int x, int y, Vector3& tangent, Vector3& binormal)
	{
		int xp = (x < hm->w-1) ? x+1 : x;
		int xm = (x > 0) ? x-1 : x;
		int yp = (y < hm->h-1) ? y+1 : y;
		int ym = (y > 0) ? y-1 : y;

		//X filter:
		//-1 0 1
		//-2 0 2
		//-1 0 1
		const int dhdx =
			int     (-hm->atSynced(xm, ym) + hm->atSynced(xp, ym)) +
			int(2 * (-hm->atSynced(xm, y)  + hm->atSynced(xp, y))) +
			int(     -hm->atSynced(xm, yp) + hm->atSynced(xp, yp));

		// 
		//Z filter:
		//-1 -2 -1
		//0  0  0
		//1  2  1
		//
		const int dhdz =
			int(hm->atSynced(xm, yp) + 2 * hm->atSynced(x, yp) + hm->atSynced(xp, yp)) -
			int(hm->atSynced(xm, ym) + 2 * hm->atSynced(x, ym) + hm->atSynced(xp, ym));

		tangent = Vector3(hm->squareSize * 2.0f, /*hm->scale * */ dhdx * 0.25f, 0.0f);
		binormal = Vector3(0.0f, dhdz * /*hm->scale * */ 0.25f, hm->squareSize * 2.0f);

//		tangent.set(vdif * 2.0f, dhdx, 0.0f);
//		binormal.set(0.0f, dhdz, vdif * 2.0f);
	}


//-----------------------------------------------------------------------
// IndexTable
//    generates index buffers for the 16 different LOD configurations a quad can be in.
//-----------------------------------------------------------------------
#define NUM_TABLES 16

	// flags that determine if a specific quad side has lower res
#define up_bit 1    // x=0 y=-1
#define left_bit 2  // x=-1 y=0
#define right_bit 4 // x=1 y=0
#define down_bit 8  // x=0 y=1

	// table of precomputed indices
	struct IndexTable
	{
		typedef unsigned short index_t;

		IndexTable();

		GLenum IndexType() const { return GL_UNSIGNED_SHORT; }

		void Calculate(int sides);

		int size[NUM_TABLES];
		IndexBuffer buffers[NUM_TABLES];
	};

};

#endif // _TERRAIN_NODE_H_