#include <epoxy/gl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "gl.h"
#include "log.h"
#include "xmalloc.h"

#define max(a, b) ((a) > (b) ? (a) : (b))

static void load_shader(GLuint shader, const char *filename);
static GLuint create_shader_program(const char *vert, const char *frag);
static void GLAPIENTRY MessageCallback(
		GLenum source,
		GLenum type,
		GLuint id,
		GLenum severity,
		GLsizei length,
		const GLchar* message,
		const void* userParam);
static const char *gl_debug_source_string(GLenum type);
static const char *gl_debug_type_string(GLenum type);
static const char *gl_debug_severity_string(GLenum type);


void gl_initialise(struct gl *gl, struct image *texture)
{
#ifdef DEBUG
	//glEnable(GL_DEBUG_OUTPUT);
	//glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS);
	//glDebugMessageCallback(MessageCallback, 0);
#endif
	if (texture == NULL || texture->buffer == NULL) {
		return;
	}

	/* Compile and link the shader programs */
	gl->shader = create_shader_program(
			SHADER_PATH "vert.vert",
			SHADER_PATH "frag.frag"
			);
	glUseProgram(gl->shader);
	glUniform1i(glGetUniformLocation(gl->shader, "tex"), 0);

	/* Create a vertex buffer for a quad filling the screen */
	float vertices[] = {
		//  Position      Texcoords
		-1.0f,  1.0f, 0.0f, 0.0f, // Top-left
		1.0f,  1.0f,  1.0f, 0.0f, // Top-right
		1.0f, -1.0f,  1.0f, 1.0f, // Bottom-right
		-1.0f, -1.0f, 0.0f, 1.0f  // Bottom-left
	};

	glGenBuffers(1, &gl->vbo);
	glBindBuffer(GL_ARRAY_BUFFER, gl->vbo);
	glBufferData(
			GL_ARRAY_BUFFER,
			sizeof(vertices),
			vertices,
			GL_STATIC_DRAW);

	/*
	 * Create a vertex array and enable vertex attributes for the shaders.
	 */
	glGenVertexArrays(1, &gl->vao);
	glBindVertexArray(gl->vao);

	GLint posAttrib = glGetAttribLocation(gl->shader, "position");
	glVertexAttribPointer(
			posAttrib,
			2,
			GL_FLOAT,
			GL_FALSE,
			4*sizeof(float),
			0);
	glEnableVertexAttribArray(posAttrib);

	GLint texAttrib = glGetAttribLocation(gl->shader, "texcoord");
	glVertexAttribPointer(
			texAttrib,
			2,
			GL_FLOAT,
			GL_FALSE,
			4*sizeof(float),
			(void *)(2*sizeof(float)));
	glEnableVertexAttribArray(texAttrib);

	glBindVertexArray(0);

	/*
	 * Create the element buffer object that will actually be drawn via
	 * glDrawElements().
	 */
	GLubyte elements[] = {
		0, 1, 2,
		2, 3, 0
	};

	glGenBuffers(1, &gl->ebo);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, gl->ebo);
	glBufferData(
			GL_ELEMENT_ARRAY_BUFFER,
			sizeof(elements),
			elements,
			GL_STATIC_DRAW);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	/* Create the texture we'll draw to */
	glGenTextures(1, &gl->texture);
	glBindTexture(GL_TEXTURE_2D, gl->texture);
	glTexImage2D(
			GL_TEXTURE_2D,
			0,
			GL_RGBA,
			texture->width,
			texture->height,
			0,
			/*
			 * On little-endian processors, textures from Cairo
			 * have to have their red and blue channels swapped.
			 */
			texture->swizzle ? GL_BGRA : GL_RGBA,
			GL_UNSIGNED_BYTE,
			(GLvoid *)texture->buffer);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

	/* Bind the actual bits we'll be using to render */
	glBindVertexArray(gl->vao);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, gl->ebo);
}

void gl_destroy(struct gl *gl)
{
	glDeleteProgram(gl->shader);
	glDeleteTextures(1, &gl->texture);
	glDeleteBuffers(1, &gl->ebo);
	glDeleteVertexArrays(1, &gl->vao);
	glDeleteBuffers(1, &gl->vbo);
}

void gl_clear(struct gl *gl, struct color *color)
{
	glClearColor(color->r, color->g, color->b, color->a);
	glClear(GL_COLOR_BUFFER_BIT);
}

void gl_draw_texture(
		struct gl *gl,
		struct image *texture,
		int32_t x,
		int32_t y,
		int32_t width,
		int32_t height)
{
	if (texture->redraw) {
		glTexSubImage2D(
				GL_TEXTURE_2D,
				0,
				0,
				0,
				texture->width,
				texture->height,
				texture->swizzle ? GL_BGRA : GL_RGBA,
				GL_UNSIGNED_BYTE,
				(GLvoid *)texture->buffer);
		texture->redraw = false;
	}

	glViewport(x, y, width, height);
	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, NULL);
}

void load_shader(GLuint shader, const char *filename)
{
	errno = 0;
	FILE *fp = fopen(filename, "rb");
	if (!fp) {
		log_error("Failed to load shader %s: %s.\n",
				filename, strerror(errno));
		exit(EXIT_FAILURE);
	}
	if (fseek(fp, 0, SEEK_END) != 0) {
		log_error("Failed to load shader %s: %s.\n",
				filename, strerror(errno));
		fclose(fp);
		exit(EXIT_FAILURE);
	}
	long size = ftell(fp);
	if (size <= 0) {
		log_error("Failed to load shader %s: %s.\n",
				filename, strerror(errno));
		fclose(fp);
		exit(EXIT_FAILURE);
	}
	unsigned long usize = (unsigned long) size;
	GLchar *source = xmalloc(usize + 1);
	rewind(fp);
	if (fread(source, 1, usize, fp) != usize) {
		log_error("Failed to load shader %s: %s.\n",
				filename, strerror(errno));
		fclose(fp);
		exit(EXIT_FAILURE);
	}
	fclose(fp);
	source[usize] = '\0';
	glShaderSource(shader, 1, (const GLchar *const *)&source, NULL);
	free(source);

	glCompileShader(shader);

	GLint status;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
	if (status != GL_TRUE) {
		log_error("Failed to compile shader %s!\n", filename);

		GLint info_length = 0;
		glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &info_length);
		if (info_length > 1) {
			char *log = xmalloc((unsigned)info_length * sizeof(*log));
			glGetShaderInfoLog(shader, info_length, NULL, log);
			log_error("\t%s\n", log);
			free(log);
		}
		exit(EXIT_FAILURE);
	}
}

GLuint create_shader_program(const char *vert, const char *frag)
{
	GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
	load_shader(vertex_shader, vert);

	GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
	load_shader(fragment_shader, frag);

	GLuint shader = glCreateProgram();
	glAttachShader(shader, vertex_shader);
	glAttachShader(shader, fragment_shader);
	glLinkProgram(shader);
	glDetachShader(shader, fragment_shader);
	glDetachShader(shader, vertex_shader);
	glDeleteShader(fragment_shader);
	glDeleteShader(vertex_shader);
	return shader;
}

void GLAPIENTRY MessageCallback(
		GLenum source,
		GLenum type,
		GLuint id,
		GLenum severity,
		GLsizei length,
		const GLchar* message,
		const void* userParam)
{
	log_debug("Message from OpenGL:\n");
	log_debug("\tSource: %s\n", gl_debug_source_string(source));
	log_debug("\tType: %s\n", gl_debug_type_string(type));
	log_debug("\tSeverity: %s\n", gl_debug_severity_string(severity));
	log_debug("\tMessage: %s\n", message);
}

const char *gl_debug_source_string(GLenum type)
{
	switch(type) {
		case GL_DEBUG_SOURCE_API:
			return "API";
		case GL_DEBUG_SOURCE_WINDOW_SYSTEM:
			return "Window system";
		case GL_DEBUG_SOURCE_SHADER_COMPILER:
			return "Shader compiler";
		case GL_DEBUG_SOURCE_THIRD_PARTY:
			return "Third party";
		case GL_DEBUG_SOURCE_APPLICATION:
			return "Application";
		case GL_DEBUG_SOURCE_OTHER:
			return "Other";
	}
	return "unknown";
}

const char *gl_debug_type_string(GLenum type)
{
	switch(type) {
		case GL_DEBUG_TYPE_ERROR:
			return "Error";
		case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR:
			return "Deprecated behavior";
		case GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR:
			return "Undefined behavior";
		case GL_DEBUG_TYPE_PORTABILITY:
			return "Portability";
		case GL_DEBUG_TYPE_PERFORMANCE:
			return "Performance";
		case GL_DEBUG_TYPE_MARKER:
			return "Marker";
		case GL_DEBUG_TYPE_PUSH_GROUP:
			return "Push group";
		case GL_DEBUG_TYPE_POP_GROUP:
			return "Pop group";
		case GL_DEBUG_TYPE_OTHER:
			return "Other";
	}
	return "Unknown";
}

const char *gl_debug_severity_string(GLenum type)
{
	switch(type) {
		case GL_DEBUG_SEVERITY_HIGH:
			return "High";
		case GL_DEBUG_SEVERITY_MEDIUM:
			return "Medium";
		case GL_DEBUG_SEVERITY_LOW:
			return "Low";
		case GL_DEBUG_SEVERITY_NOTIFICATION:
			return "Notification";
	}
	return "Unknown";
}