static GLuint
compile_shader(char* contents, size_t size, unsigned int type);

static GLuint
create_shader(char* buf, size_t size);


void
render_mgr_startup(void)
{
	// Geometry rendering
	{
#ifdef BUILD_DEBUG
		size_t size;
		char* buf = DEBUG_load_shader("shaders/geo.glsl", &size);
#else
		size_t size = strlen(geo_glsl);
		char* buf = (char*)geo_glsl;
#endif

		GLuint shader = create_shader(buf, size);

		GLuint u_model = glGetUniformLocation(shader, "u_model");
		GLuint u_view = glGetUniformLocation(shader, "u_view");
		GLuint u_proj = glGetUniformLocation(shader, "u_proj");
		GLuint u_texture = glGetUniformLocation(shader, "u_texture");
		GLuint u_light = glGetUniformLocation(shader, "u_light");

		const float n = 0.1f;
		const float f = 100.0f;
		const float fov = 75.0f;
		const float d = 1.0f / tanf(DEG_TO_RAD(fov*0.5f));
		const float a = (float)RENDER_WIDTH / (float)RENDER_HEIGHT;

		mat4 proj_mat = {
			d/a,  0.0f, 0.0f,    0.0f,
			0.0f, d,    0.0f,    0.0f,
			0.0f, 0.0f, f/(f-n), (-f*n)/(f-n),
			0.0f, 0.0f, 1.0f,    0.0f
		};

		g_engine->render_mgr.geo.shader = shader;
		g_engine->render_mgr.geo.u_model = u_model;
		g_engine->render_mgr.geo.u_proj = u_proj;
		g_engine->render_mgr.geo.u_view= u_view;
		g_engine->render_mgr.geo.u_texture = u_texture;
		g_engine->render_mgr.geo.u_light = u_light;
		g_engine->render_mgr.geo.proj_mat = proj_mat;
	}

	// Text rendering
	{
#ifdef BUILD_DEBUG
		size_t size;
		char* buf = DEBUG_load_shader("shaders/text.glsl", &size);
#else
		size_t size = strlen(text_glsl);
		char* buf = (char*)text_glsl;
#endif

		GLuint shader = create_shader(buf, size);

		GLuint vao;
		glGenVertexArrays(1, &vao);
		glBindVertexArray(vao);

		GLuint vbo;
		glGenBuffers(1, &vbo);
		glBindBuffer(GL_ARRAY_BUFFER, vbo);

		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)0);

		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(2 * sizeof(float)));

		GLuint texture;
		glGenTextures(1, &texture);
		glBindTexture(GL_TEXTURE_2D, texture);
		glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, g_font.width, g_font.height, 0, GL_RED, GL_UNSIGNED_BYTE, g_font.bitmap);

		GLuint u_proj = glGetUniformLocation(shader, "u_proj");
		GLuint u_model = glGetUniformLocation(shader, "u_model");
		GLuint u_texture = glGetUniformLocation(shader, "u_texture");
		GLuint u_color = glGetUniformLocation(shader, "u_color");

		mat4 proj_mat =
		{
			2.0f/WINDOW_WIDTH, 0.0f,               0.0f,  -1.0f,
			0.0f,              2.0f/WINDOW_HEIGHT, 0.0f,  -1.0f,
			0.0f,              0.0f,              -1.0f,  -1.0f,
			0.0f,              0.0f,               0.0f,   1.0f
		};

		g_engine->render_mgr.text.shader = shader;
		g_engine->render_mgr.text.vao = vao;
		g_engine->render_mgr.text.vbo = vbo;
		g_engine->render_mgr.text.texture = texture;
		g_engine->render_mgr.text.u_proj = u_proj;
		g_engine->render_mgr.text.u_model = u_model;
		g_engine->render_mgr.text.u_texture = u_texture;
		g_engine->render_mgr.text.u_color = u_color;
		g_engine->render_mgr.text.proj_mat = proj_mat;
	}

	// Screen rendering
	{
#ifdef BUILD_DEBUG
		size_t size;
		char* buf = DEBUG_load_shader("shaders/screen.glsl", &size);
#else
		size_t size = strlen(screen_glsl);
		char* buf = (char*)screen_glsl;
#endif

		GLuint shader = create_shader(buf, size);

		// Low-resolution texture that will be rendered into
		GLuint texture;
		glGenTextures(1, &texture);
		glBindTexture(GL_TEXTURE_2D, texture);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, RENDER_WIDTH, RENDER_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		glBindTexture(GL_TEXTURE_2D, 0);

		// Render buffer object required for the framebuffer
		GLuint rbo;
		glGenRenderbuffers(1, &rbo);
		glBindRenderbuffer(GL_RENDERBUFFER, rbo);
		glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, RENDER_WIDTH, RENDER_HEIGHT);
		glBindRenderbuffer(GL_RENDERBUFFER, 0);

		// Framebuffer attached to texture and RBO
		GLuint fbo;
		glGenFramebuffers(1, &fbo);
		glBindFramebuffer(GL_FRAMEBUFFER, fbo);
		glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
		glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rbo);

		if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
			LOG_ERROR("Unable to create render-to-texture framebuffer.");
			exit(EXIT_FAILURE);
		}

		glBindFramebuffer(GL_FRAMEBUFFER, 0);

		float vertices[] =
		{
			// Position     Texcoord
			-1.0f,  1.0f, 0.0f, 1.0f, // upper left
			-1.0f, -1.0f, 0.0f, 0.0f, // lower left
			1.0f, -1.0f, 1.0f, 0.0f, // lower right
			1.0f, -1.0f, 1.0f, 0.0f, // lower right
			1.0f,  1.0f, 1.0f, 1.0f, // upper right
			-1.0f,  1.0f, 0.0f, 1.0f, // upper left
		};

		GLuint vao;
		glGenVertexArrays(1, &vao);
		glBindVertexArray(vao);

		GLuint vbo;
		glGenBuffers(1, &vbo);
		glBindBuffer(GL_ARRAY_BUFFER, vbo);
		glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

		glEnableVertexAttribArray(0);
		glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(vertices[0]), (void*)0);

		glEnableVertexAttribArray(1);
		glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(vertices[0]), (void*)(2 * sizeof(vertices[0])));

		glBindVertexArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, 0);

		GLuint u_texture = glGetUniformLocation(shader, "u_texture");

		g_engine->render_mgr.screen.shader = shader;
		g_engine->render_mgr.screen.vao = vao;
		g_engine->render_mgr.screen.vbo = vbo;
		g_engine->render_mgr.screen.fbo = fbo;
		g_engine->render_mgr.screen.rbo = rbo;
		g_engine->render_mgr.screen.texture = texture;
		g_engine->render_mgr.screen.u_texture = u_texture;
	}
}

const char*
format_text(const char* format, ...)
{
	static char buf[MAX_TEXT_LENGTH] = {};

	va_list args;
	va_start(args, format);
	vsprintf(buf, format, args);
	va_end(args);

	return buf;
}

void
render_geo_begin(void)
{
	glBindFramebuffer(GL_FRAMEBUFFER, g_engine->render_mgr.screen.fbo);
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glEnable(GL_DEPTH_TEST);
	glEnable(GL_BLEND);

	glUseProgram(g_engine->render_mgr.geo.shader);
	glViewport(0, 0, RENDER_WIDTH, RENDER_HEIGHT);
	glUniformMatrix4fv(g_engine->render_mgr.geo.u_proj, 1, GL_TRUE, (float*)&g_engine->render_mgr.geo.proj_mat);

#ifdef BUILD_DEBUG
	if (g_debug->camera.enabled) {
		glUniformMatrix4fv(g_engine->render_mgr.geo.u_view, 1, GL_TRUE, (float*)&g_debug->camera.fly.view_mat);
	}
	else {
		glUniformMatrix4fv(g_engine->render_mgr.geo.u_view, 1, GL_TRUE, (float*)&g_engine->render_mgr.active_camera->view_mat);
	}
#else
		glUniformMatrix4fv(g_engine->render_mgr.geo.u_view, 1, GL_TRUE, (float*)&g_engine->render_mgr.active_camera->view_mat);
#endif
}

void
render_geo_end(void)
{
	glBindFramebuffer(GL_FRAMEBUFFER, 0);
	glViewport(VIEWPORT_X, VIEWPORT_Y, VIEWPORT_WIDTH, VIEWPORT_HEIGHT);
}

void
render_screen_begin(void)
{
	glClear(GL_COLOR_BUFFER_BIT);
	glEnable(GL_BLEND);

	glUseProgram(g_engine->render_mgr.screen.shader);
	glBindVertexArray(g_engine->render_mgr.screen.vao);
	glUniform1i(g_engine->render_mgr.screen.u_texture, 0);
}

void
render_screen_end(void)
{
	glDisable(GL_DEPTH_TEST);

	glBindTexture(GL_TEXTURE_2D, g_engine->render_mgr.screen.texture);
	glDrawArrays(GL_TRIANGLES, 0, 6);
	glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
}

void
render_text(const char* text, vec2 position, vec3 color, float size)
{
	struct vertex {
		vec2 position;
		vec2 texcoord;
	};

	struct vertex vertices[6 * MAX_TEXT_LENGTH];

	int text_length = strlen(text);
	LOG_ASSERT(text_length < MAX_TEXT_LENGTH,
		"Text length (%d) exceeds allowed maximum (%d)", text_length, MAX_TEXT_LENGTH);

	float atlas_width_recip = 1.0f / g_font.width;
	float atlas_height_recip = 1.0f / g_font.height;
	int cursor = 0;

	for (int i = 0; i < text_length; i++)
	{
		// Indices start with space character (ASCII 0x20 / 32)
		int idx = text[i] - ' ';
		glyph_t glyph = g_font.glyphs[idx];

		// Set up the four vertices required for the glyph's quad (texcoord.y is flipped to account for flipped texture)
		struct vertex upper_left = {
			.position.x = cursor - glyph.origin_x,
			.position.y = glyph.origin_y,
			.texcoord.x = glyph.x * atlas_width_recip,
			.texcoord.y = 1.0f - (glyph.y * atlas_height_recip)};

		struct vertex upper_right = {
			.position.x = upper_left.position.x + glyph.width,
			.position.y = upper_left.position.y,
			.texcoord.x = (glyph.x + glyph.width) * atlas_width_recip,
			.texcoord.y = upper_left.texcoord.y};

		struct vertex bottom_right = {
			.position.x = upper_right.position.x,
			.position.y = upper_left.position.y - glyph.height,
			.texcoord.x = upper_right.texcoord.x,
			.texcoord.y = 1.0f - ((glyph.y + glyph.height) * atlas_height_recip)};

		struct vertex bottom_left = {
			.position.x = upper_left.position.x,
			.position.y = bottom_right.position.y,
			.texcoord.x = upper_left.texcoord.x,
			.texcoord.y = bottom_right.texcoord.y};

		// o-----o
		// | \   |
		// |  \  |
		// |   \ |
		// o-----o

		vertices[6*i + 0] = upper_left;
		vertices[6*i + 1] = upper_right;
		vertices[6*i + 2] = bottom_right;
		vertices[6*i + 3] = bottom_right;
		vertices[6*i + 4] = bottom_left;
		vertices[6*i + 5] = upper_left;

		cursor += g_font.advance;
	}

	mat4 model_mat = mat4_identity();
	model_mat.e00 = size;
	model_mat.e11 = size;
	model_mat.e03 = position.x;
	model_mat.e13 = position.y;

	glUseProgram(g_engine->render_mgr.text.shader);
	glUniformMatrix4fv(g_engine->render_mgr.text.u_proj, 1, GL_TRUE, (float*)&g_engine->render_mgr.text.proj_mat);
	glUniformMatrix4fv(g_engine->render_mgr.text.u_model, 1, GL_TRUE, (float*)&model_mat);
	glUniform1i(g_engine->render_mgr.text.u_texture, 0);
	glUniform3fv(g_engine->render_mgr.text.u_color, 1, (float*)&color);

	glBindVertexArray(g_engine->render_mgr.text.vao);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, g_engine->render_mgr.text.texture);
	glBindBuffer(GL_ARRAY_BUFFER, g_engine->render_mgr.text.vbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices[0]) * 6 * text_length, vertices, GL_DYNAMIC_DRAW);

	glDrawArrays(GL_TRIANGLES, 0, 6 * text_length);
}

void
set_active_camera(camera_t* camera)
{
	g_engine->render_mgr.active_camera = camera;
}

camera_t*
get_active_camera(void)
{
	return g_engine->render_mgr.active_camera;
}

static GLuint
compile_shader(char* contents, size_t size, unsigned int type)
{
	const char* sources[3];
	sources[0] = "#version 400 core\n";
	sources[1] = (type == GL_VERTEX_SHADER) ? "#define VERTEX\n" : "#define FRAGMENT\n";
	sources[2] = contents;

	int lengths[3];
	lengths[0] = strlen(sources[0]);
	lengths[1] = strlen(sources[1]);
	lengths[2] = size;

	GLuint id = glCreateShader(type);
	glShaderSource(id, 3, sources, lengths);
	glCompileShader(id);

	char log[512];
	int success;
	glGetShaderiv(id, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(id, sizeof(log), NULL, log);

		LOG_ERROR("Failed to compile shader:");
		LOG_ERROR("    %s", log);

#ifndef BUILD_DEBUG
		exit(EXIT_FAILURE);
#endif
	}

	return id;
}

static GLuint
create_shader(char* buf, size_t size)
{
	size_t vertex_size;
	{
		char* substring = strstr(buf, "#ifdef FRAGMENT");
		LOG_ASSERT(substring != NULL, "Error parsing vertex shader");

		vertex_size = substring - buf;
	}

	size_t fragment_size;
	{
		fragment_size = size - vertex_size;
	}

	GLuint vertex = compile_shader(buf, vertex_size, GL_VERTEX_SHADER);
	GLuint fragment = compile_shader(buf+vertex_size, fragment_size, GL_FRAGMENT_SHADER);

	GLuint shader = glCreateProgram();
	{
		char log[512];
		int success;

		glAttachShader(shader, vertex);
		glAttachShader(shader, fragment);
		glLinkProgram(shader);
		glGetProgramiv(shader, GL_LINK_STATUS, &success);
		if (!success)
		{
			glGetProgramInfoLog(shader, sizeof(log), NULL, log);

			LOG_ERROR("Failed to link shader program:");
			LOG_ERROR("    %s", log);

#ifndef BUILD_DEBUG
			exit(EXIT_FAILURE);
#endif
		}

		glDeleteShader(vertex);
		glDeleteShader(fragment);
	}

	return shader;
}