/**
 * From the OpenGL Programming wikibook: http://en.wikibooks.org/wiki/OpenGL_Programming
 * This file is in the public domain.
 * Contributors: Sylvain Beucler, Guus Sliepen
 */

#include <iostream>
using namespace std;

#include <SDL.h>
#include <SDL_opengles2.h>

/**
 * Store all the file's contents in memory, useful to pass shaders
 * source code to OpenGL.  Using SDL_RWops for Android asset support.
 */
char* file_read(const char* filename) {
	SDL_RWops *rw = SDL_RWFromFile(filename, "rb");
	if (rw == NULL) return NULL;
	
	Sint64 res_size = SDL_RWsize(rw);
	char* res = new char[res_size + 1];

	Sint64 nb_read_total = 0, nb_read = 1;
	char* buf = res;
	while (nb_read_total < res_size && nb_read != 0) {
		nb_read = SDL_RWread(rw, buf, 1, (res_size - nb_read_total));
		nb_read_total += nb_read;
		buf += nb_read;
	}
	SDL_RWclose(rw);
	if (nb_read_total != res_size) {
		delete[] res;
		return NULL;
	}
	
	res[nb_read_total] = '\0';
	return res;
}

/**
 * Display compilation errors from the OpenGL shader compiler
 */
void print_log(GLuint object) {
	GLint log_length = 0;
	if (glIsShader(object)) {
		glGetShaderiv(object, GL_INFO_LOG_LENGTH, &log_length);
	} else if (glIsProgram(object)) {
		glGetProgramiv(object, GL_INFO_LOG_LENGTH, &log_length);
	} else {
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR,
					   "printlog: Not a shader or a program");
		return;
	}

	char log[log_length];
	
	if (glIsShader(object))
		glGetShaderInfoLog(object, log_length, NULL, log);
	else if (glIsProgram(object))
		glGetProgramInfoLog(object, log_length, NULL, log);
	
	SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR, "%s\n", log);
}

/**
 * Compile the shader from file 'filename', with error handling
 */
GLuint create_shader(const char* filename, GLenum type) {
	const char* source = file_read(filename);
	if (source == NULL) {
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR,
					   "Error opening %s: %s", filename, SDL_GetError());
		return 0;
	}
	GLuint res = glCreateShader(type);
	const GLchar* sources[] = {
		// Define GLSL version
		"#version 100\n"  // OpenGL ES 2.0
		,
		// Define default float precision for fragment shaders:
		(type == GL_FRAGMENT_SHADER) ?
		"#ifdef GL_FRAGMENT_PRECISION_HIGH\n"
		"precision highp float;           \n"
		"#else                            \n"
		"precision mediump float;         \n"
		"#endif                           \n"
		: ""
		,
		source };
	glShaderSource(res, 3, sources, NULL);
	delete[] source;
	
	glCompileShader(res);
	GLint compile_ok = GL_FALSE;
	glGetShaderiv(res, GL_COMPILE_STATUS, &compile_ok);
	if (compile_ok == GL_FALSE) {
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR, "%s:\n", filename);
		print_log(res);
		glDeleteShader(res);
		return 0;
	}
	
	return res;
}

GLuint create_program(const char *vertexfile, const char *fragmentfile) {
	GLuint program = glCreateProgram();
	GLuint shader;

	if(vertexfile) {
		shader = create_shader(vertexfile, GL_VERTEX_SHADER);
		if(!shader)
			return 0;
		glAttachShader(program, shader);
	}

	if(fragmentfile) {
		shader = create_shader(fragmentfile, GL_FRAGMENT_SHADER);
		if(!shader)
			return 0;
		glAttachShader(program, shader);
	}

	glLinkProgram(program);
	GLint link_ok = GL_FALSE;
	glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
	if (!link_ok) {
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO, "glLinkProgram:");
		print_log(program);
		glDeleteProgram(program);
		return 0;
	}

	return program;
}

GLint get_attrib(GLuint program, const char *name) {
	GLint attribute = glGetAttribLocation(program, name);
	if(attribute == -1)
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR,
					   "Could not bind attribute %s", name);
	return attribute;
}

GLint get_uniform(GLuint program, const char *name) {
	GLint uniform = glGetUniformLocation(program, name);
	if(uniform == -1)
		SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_ERROR,
					   "Could not bind uniform %s", name);
	return uniform;
}

void print_opengl_info() {
	int major, minor, profile;
	SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major);
	SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor);
	SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile);
	const char* profile_str = "";
	if (profile & SDL_GL_CONTEXT_PROFILE_CORE)
		profile_str = "CORE";
	if (profile & SDL_GL_CONTEXT_PROFILE_COMPATIBILITY)
		profile_str = "COMPATIBILITY";
	if (profile & SDL_GL_CONTEXT_PROFILE_ES)
		profile_str = "ES";

	SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO,
				   "OpenGL %d.%d %s", major, minor, profile_str);
}