#ifndef RENDERER_H
#define RENDERER_H

#include <vector>
#include <cmath> // trig functions
#include <cstdlib> // calloc

// TODO: decide on extension library
//#include <GL/glew.h>
#include <GL/gl3w.h>

#include <SDL.h>
#include <glm/glm.hpp>
#include <glm/geometric.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include "hexlib.h"
#include "hexgame.h"

#define MOVE_SPEED 5.f
#define ROTATE_SPEED 0.005f
#define CAMERA_Z_CLAMP_ANGLE 85.f
//#define PROJ_TYPE ORTHOGRAPHIC
#define PROJ_TYPE PERSPECTIVE

const char * VERTEX_SHADER_CODE =
	"#version 330 core\n"
	"in vec3 vertexPosition_modelspace;\n"
	"in vec3 vertexColor;\n"
	"out vec3 fragmentColor;\n"
	"uniform mat4 model;\n"
	"uniform mat4 view;\n"
	"uniform mat4 projection;\n"
	"void main()\n"
	"{\n"
	"	gl_Position = projection * view * model * vec4(vertexPosition_modelspace, 1);\n"
	"	fragmentColor = vertexColor;\n"
	"}";

const char * FRAGMENT_SHADER_CODE =
	"#version 330 core\n"
	"in vec3 fragmentColor;\n"
	"out vec3 color;\n"
	"void main()\n"
	"{\n"
	"	color = fragmentColor;\n"
	"}";

const char * LINE_FRAGMENT_SHADER_CODE =
	"#version 330 core\n"
	"out vec3 color;\n"
	"void main()\n"
	"{\n"
	"	color = vec3(0,0,0);\n"
	"}";

const char * DEBUG_FRAGMENT_SHADER_CODE =
	"#version 330 core\n"
	"out vec3 color;\n"
	"void main()\n"
	"{\n"
	"	color = vec3(1,0,0);\n"
	"}";

typedef struct clear_col
{
	real32 R;
	real32 G;
	real32 B;
	real32 A;
} clear_col;
clear_col g_clear_col { 75.f / 255.f, 135.f / 255.f, 135.f / 255.f, 1.f };

typedef struct gl_matrix_info
{
	glm::mat4 projection;
	glm::mat4 view;
	glm::mat4 model;
	glm::mat4 MVP;
} gl_matrix_info;

enum projection_type
{
	PERSPECTIVE,
	ORTHOGRAPHIC,
};

struct camera
{
	glm::vec3 position;
	float hAngle;
	float vAngle;
	glm::vec3 target;
	glm::vec3 forward;
	glm::vec3 up;
	glm::vec3 left;
};

typedef struct gl_buffer
{
	GLuint buffer_id = 0;
	size_t buffer_len = 0; // NOTE: number of elements in buffer
	GLfloat* buffer = nullptr;
} gl_buffer;

typedef struct gl_render_group
{
	// NOTE: For now the renderFrame function will assume these are the same size
	gl_buffer vertex_buffer;
	gl_buffer color_buffer;
	GLuint program_id = 0;
	GLuint model_matrix_id = 0;
	GLuint view_matrix_id = 0;
	GLuint projection_matrix_id = 0;
	GLuint vertex_array_id = 0;
	Entity* entity = nullptr;
} gl_render_group;

gl_matrix_info g_scene_matrices;
gl_render_group g_filled_hex_render_group;
gl_render_group g_hex_line_render_group;
gl_render_group g_debug_render_group;
gl_render_group g_entity_render_group;
camera g_camera;

// Interface

bool initRenderer(SDL_Handles &handles, v2i vpDims);
bool addTexture(SDL_Handles &handles, const char * path);
bool createScene(std::vector<hex_info>* hexes, Entity* entities, uint32 entity_count);
void moveCamera(bool up, bool left, bool down, bool right, bool forward, bool backward);
void rollCamera(bool CW, bool CCW);
void rotateCamera(int32	xrel, int32 yrel);
void renderFrame(const std::vector<hex_info> *hexes);
void renderDebug(std::vector<Point> &vertices);
void freeBuffers();

// forward declarations

bool initShaderProgram(gl_render_group &rg, const char * vertex_code, const char * frag_code,
		const char* model_name, const char* view_name, const char* projection_name);
// enable debug output https://www.khronos.org/opengl/wiki/OpenGL_Error
void openglDebugCallback(GLenum source, GLenum type, GLuint id, GLenum severity,
						GLsizei length, const GLchar* message, const void* userParam);
void fillTriangleBufferFromHex(GLfloat buf[], int idx,  const hex_info &hex);
void fillColorBuffer(GLfloat buf[], int len, std::vector<hex_info> *hexes);
void convertColor(GLfloat buf[], uint32 color);
void fillHexLineBuffer(GLfloat buf[], int len, std::vector<hex_info>* hexes);
bool checkGLBufferSize(GLenum buf_type, int expected_size, int line_num);
bool initGLBufferObject(gl_buffer* buf_obj, int len, GLenum usage, GLfloat data[]);
void drawRenderGroup(gl_render_group* rg, GLenum draw_mode, bool update_vertex_data);
void initMatrices(projection_type p);

bool
initRenderer(SDL_Handles &handles, v2i vpDims)
{
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	// TODO: Line drawing quality seems to depend on graphics driver whims
	// 	maybe try using textured billboards instead?
	//SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
	//SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 4);
	SDL_GL_SetSwapInterval(1);	// vsync
	SDL_GetCurrentDisplayMode(0, &handles.currentDisplayMode);
	handles.window = 
		SDL_CreateWindow("hexgame", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
							vpDims.x, vpDims.y, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
	
	if (handles.window == NULL)
	{
		// TODO: log error SDL_GetError()
		return false;
	}

	handles.glContext = SDL_GL_CreateContext(handles.window);
	
	// TODO: decide on extension library
	gl3wInit();
#if 0
	// Initialize GLEW
	// glewExperimental is only needed in GLEW <= 1.13.0
	// we can require version 2.0.0+
	//glewExperimental = true; // Needed for core profile
	GLenum err = glewInit();
	if (err != GLEW_OK) {
		LOG(ERROR) << "Failed to initilize GLEW" << glewGetErrorString(err) << "\n";
		return false;
	}
#endif

	LOG(INFO) << "opengl vendor: " << glGetString(GL_VENDOR) << "\n";
	LOG(INFO)<< "opengl renderer: " << glGetString(GL_RENDERER) << "\n";
	LOG(INFO) << "opengl version: " << glGetString(GL_VERSION) << "\n";
	
	glEnable(GL_DEPTH_TEST);
	glEnable(GL_LINE_SMOOTH);

	// TODO: blending, these options break the http://www.opengl-tutorial.org tutorials atm
	// Setup render state: alpha-blending enabled, polygon fill
#if 1
	glEnable(GL_BLEND);
	glBlendEquation(GL_FUNC_ADD);
	glBlendFunc(GL_ONE, GL_SRC_ALPHA);
	glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
#endif

	// TODO: glDebugMessageCallback is only availabe  from >v4.3
	//  check and warn if context doesn't support this function here
	glEnable (GL_DEBUG_OUTPUT);
	glDebugMessageCallback((GLDEBUGPROC) openglDebugCallback, 0);
	// hide VRAM debug messages
	glDebugMessageControl(GL_DONT_CARE, 33361, GL_DONT_CARE, 0, 0, GL_FALSE);
	
	if (!initShaderProgram(
				g_filled_hex_render_group, VERTEX_SHADER_CODE, FRAGMENT_SHADER_CODE,
				"model", "view", "projection")
		|| !initShaderProgram(
				g_hex_line_render_group, VERTEX_SHADER_CODE, LINE_FRAGMENT_SHADER_CODE,
				"model", "view", "projection")
		|| !initShaderProgram(
				g_debug_render_group, VERTEX_SHADER_CODE, DEBUG_FRAGMENT_SHADER_CODE,
			   "model", "view", "projection")
		|| !initShaderProgram(
				g_entity_render_group, VERTEX_SHADER_CODE, FRAGMENT_SHADER_CODE,
				"model", "view", "projection"))
	{
		return false;
	}

	return true;
}

bool
addTexture(SDL_Handles &handles, const char * path)
{
	// testing
	LOG(INFO) << "Loading image: " << path << "\n";
	SDL_Surface* image = IMG_Load(path);

	if (!image)
	{
		LOG(ERROR) << "IMG_Load: " << IMG_GetError() << "\n";
		return 1;
	}

	GLuint tex_id;
	glGenTextures(1, &tex_id);
	glBindTexture(GL_TEXTURE_2D, tex_id);
	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, image->w, image->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	// store opengl id in SDL_Surface.userdat
	image->userdata = (void*)(intptr_t) tex_id;
	handles.texSurfaces.push_back(image);

	return true;
}

v2f
getUnprojectedCoords(int32 x, int32 y, int32 vp_width, int32 vp_height)
{
	// NOTE: using depth buffer may not be as accurate as doing ray-cast
	GLfloat depth;
	glReadPixels(x, y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &depth);
	glm::vec4 viewport = glm::vec4(0, 0, vp_width, vp_height);
	glm::vec3 wincoord = glm::vec3(x, y, depth);
	glm::vec3 vU = glm::unProject(wincoord, g_scene_matrices.view, g_scene_matrices.projection, viewport);
	v2f v(vU.x, vU.y);

	return v;
}

// NOTE: model_name, view_name, and projection_name should match the matrix variable
// 	names in the shader source
bool
initShaderProgram(gl_render_group &rg, const char * vertex_code, const char * frag_code,
	const char* model_name, const char* view_name, const char* projection_name)
{
	glGenVertexArrays(1, &rg.vertex_array_id);
	glBindVertexArray(rg.vertex_array_id);
	GLuint vertex_shader_id = glCreateShader(GL_VERTEX_SHADER);
	GLuint fragment_shader_id = glCreateShader(GL_FRAGMENT_SHADER);

	glShaderSource(vertex_shader_id, 1, &vertex_code, NULL);
	glShaderSource(fragment_shader_id, 1, &frag_code, NULL);
	glCompileShader(vertex_shader_id);
	glCompileShader(fragment_shader_id);

	rg.program_id = glCreateProgram();
	glAttachShader(rg.program_id, vertex_shader_id);
	glAttachShader(rg.program_id, fragment_shader_id);
	glLinkProgram(rg.program_id);

	rg.model_matrix_id = glGetUniformLocation(rg.program_id, model_name);
	rg.view_matrix_id = glGetUniformLocation(rg.program_id, view_name);
	rg.projection_matrix_id = glGetUniformLocation(rg.program_id, projection_name);

	glDetachShader(rg.program_id, vertex_shader_id);
	glDetachShader(rg.program_id, fragment_shader_id);
	glDeleteShader(vertex_shader_id);
	glDeleteShader(fragment_shader_id);

	// check for errors
	GLint isLinked = 0;
	glGetProgramiv(rg.program_id, GL_LINK_STATUS, &isLinked);
	if (isLinked == GL_FALSE) {
		GLint maxLength = 0;
		glGetProgramiv(rg.program_id, GL_INFO_LOG_LENGTH, &maxLength);

		// The maxLength includes the NULL character
		GLchar infoLog[maxLength];
		glGetProgramInfoLog(rg.program_id, maxLength, &maxLength, &infoLog[0]);
		LOG(ERROR) << infoLog << "\n";

		// The program is useless now. So delete it.
		glDeleteProgram(rg.program_id);

		return false;
	}

	return true;
}

void
initMatrices(projection_type p)
{
	// TODO: many constants used here should be passed as args

	if (p == PERSPECTIVE)
	{
		g_scene_matrices.projection = glm::infinitePerspective(
			glm::radians(60.f), // FoV
			16.f / 9.f, // ascpect ratio
			0.1f // near clip plane
		);

		g_camera.position = glm::vec3(640,0,100); 
		g_camera.target = glm::vec3(640,500,0);
		// inital rotation should match target direction
		glm::vec3 &p = g_camera.position;
		glm::vec3 &t = g_camera.target;
		g_camera.hAngle = 0;
		g_camera.vAngle = glm::atan((t.z - p.z) / (t.y - p.y));
		
		//////
		// TODO: add call to rotate camera here to remove duplicate code
		camera &c = g_camera;
		float &h = c.hAngle;
		float &v = c.vAngle;
		c.forward = glm::vec3(
			glm::cos(v) * glm::sin(h),
			glm::cos(v) * glm::cos(h),
			glm::sin(v)
		);
		//////

		g_camera.up = glm::vec3(0,1,0);
		g_camera.left = glm::normalize(glm::cross(g_camera.up, g_camera.forward));
		g_camera.up = glm::cross(g_camera.forward, g_camera.left);

		g_scene_matrices.view = glm::lookAt(
			g_camera.position, // camera position
			g_camera.position + g_camera.forward,
			g_camera.up // "up" vector
		);
	}
	else // ORTHO
	{
		// left, right, bottom, top, zNear, zFar
		g_scene_matrices.projection = glm::ortho(0.f, 1280.0f, 0.f, 720.0f, 0.1f, 100.0f);
		g_scene_matrices.view = glm::lookAt(
			glm::vec3(0.0f, 0.0f, 1.0f),	// camera position
			glm::vec3(0.0f, 0.0f, 0.0f),	// look at position
			glm::vec3(0,1,0)				// "up" vector
		);
	}	

	g_scene_matrices.model = glm::mat4(1.0f);
	g_scene_matrices.MVP = g_scene_matrices.projection * g_scene_matrices.view * g_scene_matrices.model; 
}

bool
createScene(std::vector<hex_info>* hexes, Entity* entities, uint32 entity_count)
{
	initMatrices(PROJ_TYPE);

	// Vertex Data
	
	// TODO: index duplicate vertices
	// http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-9-vbo-indexing/
	int hex_count = (int) hexes->size();
	// 6 triangles * 3 vertices per triangle * 3 floats per vertex = 54
	int vbuf_len = hex_count * 6 * 3 * 3;
	
	// TODO: surely there's a way to use indexed drawing for line vertices eg) line_loop
	// 	and still use one buffer for multiple shapes/paths gldrawarraysintanced?, gldrawelements?
	// 	https://gamedev.stackexchange.com/questions/104310/opengl-4-5-primitive-restart-vs-base-index
	int line_vertices_per_hex = 6 * 2; // 12 vertices since we're using line segments atm
	//gl_buffer *line_vertex_buffer = &g_hex_line_render_group.vertex_buffer;
	int line_buf_len = hexes->size() * line_vertices_per_hex * 3; // 3 floats per vertex

	// temporary buffers
	GLfloat* vbuf = (GLfloat*) std::calloc(vbuf_len, sizeof(GLfloat));
	GLfloat* cbuf = (GLfloat*) std::calloc(vbuf_len, sizeof(GLfloat));
	GLfloat* line_buf = (GLfloat*) std::calloc(vbuf_len, sizeof(GLfloat));

	for (int i = 0; i < hex_count; i++)
		fillTriangleBufferFromHex(vbuf, 54 * i, (*hexes)[i]);
	

	if (!initGLBufferObject(&g_filled_hex_render_group.vertex_buffer, vbuf_len, GL_DYNAMIC_DRAW, vbuf))
		return false;

	// color data for hex vertices
	
	fillColorBuffer(cbuf, vbuf_len, hexes);

	if (!initGLBufferObject(&g_filled_hex_render_group.color_buffer, vbuf_len, GL_DYNAMIC_DRAW, cbuf))
		return false;

	// hex line vertex data
	
	fillHexLineBuffer(line_buf, line_buf_len, hexes);
	if (!initGLBufferObject(&g_hex_line_render_group.vertex_buffer, line_buf_len, GL_STATIC_DRAW, line_buf))
		return false;

	// free temporary buffers
	// TODO: temp buffers won't be freed if exit early is hit
	std::free(vbuf);
	std::free(cbuf);
	std::free(line_buf);
	vbuf = cbuf = line_buf = nullptr;

	// debug draw vertexes
	
	// 4 vertices, 3 floats per vertex
	int len = 4 * 3;
	if (!initGLBufferObject(&g_debug_render_group.vertex_buffer, len, GL_DYNAMIC_DRAW, 0))
		return false;


	///////////////
	// TODO: Testing Entities/assimp model loading

	g_entity_render_group.entity = &entities[0];
	entities[0].model_transform = glm::scale(glm::mat4(1), glm::vec3(100, 100, 100));

	uint entity_buf_len = entities[0].num_vertices * 3;
	GLfloat* entity_buf = (GLfloat*) std::calloc(entity_buf_len, sizeof(GLfloat));
	GLfloat* entity_color_buf = (GLfloat*) std::calloc(entity_buf_len, sizeof(GLfloat));

	// dump vertices into temporary buffer
	uint vertex_index = 0;
	uint vertex_prop_index = 0;
	GLfloat entity_test_color[3];
	convertColor(entity_test_color, 0xF46000FF);

	for (uint j = 0; j < entity_buf_len; j++) {
		const glm::vec3& vertex = entities[0].vertices[vertex_index];

		switch (vertex_prop_index) {
			case 0:	entity_buf[j] = vertex.x; break;
			case 1: entity_buf[j] = vertex.y; break;
			case 2: entity_buf[j] = vertex.z; break;
		}

		entity_color_buf[j] = entity_test_color[vertex_prop_index];
		vertex_prop_index++;

		if (vertex_prop_index == 3) {
			vertex_prop_index = 0;
			vertex_index++;
		}
	}

	if (!initGLBufferObject(&g_entity_render_group.vertex_buffer, entity_buf_len,
			GL_DYNAMIC_DRAW, entity_buf))
		return false;

	if (!initGLBufferObject(&g_entity_render_group.color_buffer, entity_buf_len,
			GL_DYNAMIC_DRAW, entity_color_buf))
		return false;

	std::free(entity_buf);
	std::free(entity_color_buf);
	entity_buf = entity_color_buf = nullptr;

	/////////

	return true;
}

void
moveCamera(bool up, bool left, bool down, bool right, bool forward, bool backward)
{
	if (!up && !left && !down && !right && !forward && !backward)
		return;

	glm::vec3 f = g_camera.forward;
	glm::vec3 u = g_camera.up;
	glm::vec3 old = g_camera.position;
	glm::vec3 &p = g_camera.position;
	glm::vec3 v(0.f); // normalized direction
	
	if (forward) v += f;
	if (backward) v -= f;
	if (up) v += u;
	if (down) v -= u;
	if (left)
	{
		glm::vec3 l = glm::cross(f, u);
		v -= l;
	}
	if (right)
	{
		glm::vec3 r = glm::cross(u, f);
		v -= r;
	}

	// TODO: this still doesn't fix side to side movement magnitude when vAngle is
	// 	close to +- 90 degrees
	glm::normalize(v);
	p += (v * MOVE_SPEED);
	glm::vec3 diff = old - p;
	g_scene_matrices.view = glm::translate(g_scene_matrices.view, diff);
	g_scene_matrices.MVP = g_scene_matrices.projection * g_scene_matrices.view * g_scene_matrices.model; 
}

void
rotateCamera(int32	xrel, int32 yrel)
{
	camera &c = g_camera;
	float &h = c.hAngle;
	float &v = c.vAngle;
	h += ROTATE_SPEED * xrel;
	v -= ROTATE_SPEED * yrel;

	// clamp vAngle to prevent gimbal lock
	float a = glm::radians(CAMERA_Z_CLAMP_ANGLE);
	if (v < (-1 * a)) v = (-1 * a);
	if (v > a) v = a;
	
	c.forward = glm::vec3(
		glm::cos(v) * glm::sin(h),
		glm::cos(v) * glm::cos(h),
		glm::sin(v)
	);

	c.up = glm::vec3(0,0,1);
	c.left = glm::cross(c.forward, c.up);

	g_scene_matrices.view = glm::lookAt(c.position, c.position + c.forward, c.up);
	g_scene_matrices.MVP = g_scene_matrices.projection * g_scene_matrices.view * g_scene_matrices.model; 
}

// NOTE: don't need this yet
void
rollCamera(bool CW, bool CCW)
{
#if 0
	if ((!CW && !CCW) || (CW && CCW))
		return;

	float a = 0.005f;
	if (CW) a *= 1;
	if (CCW) a *= -1;
	camera &c = g_camera;
	glm::mat4 m = glm::rotate(glm::mat4(1.f), a, c.forward);
	glm::vec4 v(c.up.x, c.up.y, c.up.z, 0);
	v = v * m;
	g_camera.up = glm::vec3(v.x, v.y, v.z);
	g_scene_matrices.view *= m;
	g_scene_matrices.MVP = g_scene_matrices.projection * g_scene_matrices.view * g_scene_matrices.model; 
#endif
}

void
fillTriangleBufferFromHex(GLfloat buf[], int idx,  const hex_info &hex)
{
	// triangles
	for (int i = 0; i < 6; i++)
	{
		// vertex 0
		buf[idx + 0] = (GLfloat) hex.XPos;
		buf[idx + 1] = (GLfloat) hex.YPos;
		buf[idx + 2] = (GLfloat) 0.f;

		// vertex 1
		buf[idx + 3] = (GLfloat) hex.vertices[i].x;
		buf[idx + 4] = (GLfloat) hex.vertices[i].y;
		buf[idx + 5] = (GLfloat) 0.f;

		if (i == 5)	// re-use the first point for the last triangle
		{
			// vertex 2
			buf[idx + 6] = (GLfloat) hex.vertices[0].x;
			buf[idx + 7] = (GLfloat) hex.vertices[0].y;
			buf[idx + 8] = (GLfloat) 0.f;
		}
		else
		{
			// vertex 2
			buf[idx + 6] = (GLfloat) hex.vertices[i + 1].x;
			buf[idx + 7] = (GLfloat) hex.vertices[i + 1].y;
			buf[idx + 8] = (GLfloat) 0.f;
		}
		
		// we've added 9 GLfloats per loop
		idx += 9;
	}
}

// NOTE: helper for fillColorBuffer() to convert uint32 color to GLfloat triplet
void
convertColor(GLfloat buf[3], uint32 color)
{
	// NOTE: not using the alpha values for now
	buf[0] = (GLfloat) ((color >> 24) & 0xFF) / (GLfloat) 255; 
	buf[1] = (GLfloat) ((color >> 16) & 0xFF) / (GLfloat) 255; 
	buf[2] = (GLfloat) ((color >> 8) & 0xFF) / (GLfloat) 255; 
}

void
fillColorBuffer(GLfloat buf[], int len, std::vector<hex_info>* hexes)
{
	int buf_idx;
	int buf_len_per_hex = 54; // NOTE: 3 * 3 * 6
	GLfloat color_buf[3];
	for (int i = 0; i < (int) hexes->size(); i++)
	{
		buf_idx = i * buf_len_per_hex;
		hex_info hxi = (*hexes)[i];
		convertColor(color_buf, hxi.current_color);

		for (int j = 0; j < buf_len_per_hex; j+=3)
		{
			buf[buf_idx + j] = color_buf[0];
			buf[buf_idx + j + 1] = color_buf[1];
			buf[buf_idx + j + 2] = color_buf[2];
		}
	}
}

void
fillHexLineBuffer(GLfloat buf[], int len, std::vector<hex_info>* hexes)
{
	Point p1, p2;
	int idx = 0;
	for (int i = 0; i < (int) hexes->size(); i++)
	{
		hex_info hxi = (*hexes)[i];
		for (int j = 0; j < 6; j ++)
		{
			if (j == 5) // wrap
			{
				p1 = hxi.vertices[j];
				p2 = hxi.vertices[0];
			}
			else
			{
				p1 = hxi.vertices[j];
				p2 = hxi.vertices[j + 1];
			}
			
			buf[idx + 0] = p1.x;
			buf[idx + 1] = p1.y;
			buf[idx + 2] = 0.f;
			buf[idx + 3] = p2.x;
			buf[idx + 4] = p2.y;
			buf[idx + 5] = 0.f;
			idx += 6;
		}
	}
}

// NOTE: this will only work after a call to glBindBuffer
bool
checkGLBufferSize(GLenum buf_type, int expected_size, int line_num)
{
	GLint gl_size;
	glGetBufferParameteriv(buf_type, GL_BUFFER_SIZE ,&gl_size);

	if (expected_size != gl_size)
	{
		LOG(ERROR) << "line: " << line_num << "gl buffer size mismatch\n";
		return false;
	}

	return true;
}

bool
initGLBufferObject(gl_buffer* buf_obj, int len, GLenum usage, GLfloat data[])
{
	buf_obj->buffer_len = (size_t) len;
	buf_obj->buffer = (GLfloat*) std::calloc(len, sizeof(GLfloat));

	if (data)
	{
		for (int i = 0; i < len; i++)
			buf_obj->buffer[i] = data[i];
	}

	glGenBuffers(1, &buf_obj->buffer_id);
	glBindBuffer(GL_ARRAY_BUFFER, buf_obj->buffer_id);
	glBufferData(GL_ARRAY_BUFFER, len * sizeof(GLfloat), buf_obj->buffer, usage);

	if (!checkGLBufferSize(GL_ARRAY_BUFFER, len * sizeof(GLfloat), __LINE__))
		return false;
	
	return true;
}

void
openglDebugCallback(GLenum source, GLenum type, GLuint id, GLenum severity,
					GLsizei length, const GLchar* message, const void* userParam)
{
	LOG((type == GL_DEBUG_TYPE_ERROR) ? ERROR : DEBUG)
		<< (type == GL_DEBUG_TYPE_ERROR ? "** GL ERROR **" : "")
		<< ", type: " << type
		<< ", severity: " << severity
		<< ", message: " << message << "\n";
}

void
drawRenderGroup(gl_render_group* rg, GLenum draw_mode, bool update_vertex_data = false)
{
	glUseProgram(rg->program_id);

	// Send our transformation to the currently bound shader
	glm::mat4 model_matrix;
	if (rg->entity)
		model_matrix = rg->entity->model_transform;
	else
		model_matrix = g_scene_matrices.model;

	glUniformMatrix4fv(rg->model_matrix_id, 1, GL_FALSE, &model_matrix[0][0]);
	glUniformMatrix4fv(rg->view_matrix_id, 1, GL_FALSE, &g_scene_matrices.view[0][0]);
	glUniformMatrix4fv(rg->projection_matrix_id, 1, GL_FALSE, &g_scene_matrices.projection[0][0]);
	
	// 1st attribute buffer : vertices
	glEnableVertexAttribArray(0);
	glBindBuffer(GL_ARRAY_BUFFER, rg->vertex_buffer.buffer_id);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);
	
	if (update_vertex_data)
	{
		glBufferSubData(GL_ARRAY_BUFFER, 0, rg->vertex_buffer.buffer_len * sizeof(GLfloat),
			rg->vertex_buffer.buffer);
	}

	// 2nd attribute buffer : colors
	if (rg->color_buffer.buffer)
	{
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, rg->color_buffer.buffer_id);
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*) 0);
		
		// TODO: maybe add an option to not send color data every frame?
		glBufferSubData(GL_ARRAY_BUFFER, 0, rg->color_buffer.buffer_len * sizeof(GLfloat),
				rg->color_buffer.buffer);
	}
	// draw
	glDrawArrays(draw_mode, 0, rg->vertex_buffer.buffer_len / 3);
	
	// cleanup
	glDisableVertexAttribArray(0);
	if (rg->color_buffer.buffer)
		glDisableVertexAttribArray(1);
}

void
renderFrame(std::vector<hex_info> *hexes)
{
	glClearColor(g_clear_col.R, g_clear_col.G, g_clear_col.B, g_clear_col.A);
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

	// filled hexes

	// get new colors every frame
	gl_render_group* rg = &g_filled_hex_render_group;
	fillColorBuffer(rg->color_buffer.buffer, rg->color_buffer.buffer_len, hexes);
	drawRenderGroup(rg, GL_TRIANGLES);

	// hex lines

	drawRenderGroup(&g_hex_line_render_group, GL_LINES);

	// TODO: testing entity rendering
	drawRenderGroup(&g_entity_render_group, GL_TRIANGLES);
}

void
renderDebug(std::vector<Point> &vertices)
{
	// TODO: indexed line drawing
	real64 buf[4 * 3] = {
		vertices[0].x, vertices[0].y, 0,
		vertices[1].x, vertices[1].y, 0,
		vertices[2].x, vertices[2].y, 0,
		vertices[3].x, vertices[3].y, 0,
	};

	// copy vertexes to render group
	gl_render_group* rg = &g_debug_render_group;
	for (int i = 0; i < 12; i++)
		rg->vertex_buffer.buffer[i] = buf[i];

	drawRenderGroup(rg, GL_LINE_LOOP, true);
}

void
freeBuffers()
{
	std::vector<gl_render_group> groups = {
		g_filled_hex_render_group,
		g_hex_line_render_group,
		g_debug_render_group,
		//g_entity_render_group TODO: handle enitiy memory separately
	};
	
	for (gl_render_group group : groups)
	{
		if (group.vertex_buffer.buffer)
		{
			std::free(group.vertex_buffer.buffer);
			group.vertex_buffer.buffer = 0;
		}
	
		if (group.color_buffer.buffer)
		{
			std::free(group.color_buffer.buffer);
			group.color_buffer.buffer = 0;
		}
	}
		 
}

#endif // RENDERER_H