#include <stdio.h>
#include <GL/freeglut.h>

char* file_read(const char* filename)
{
	FILE* input = fopen(filename, "rb");
	if (input == NULL) return NULL;

	if (fseek(input, 0, SEEK_END) == -1) return NULL;
	long size = ftell(input);
	if (size == -1) return NULL;
	if (fseek(input, 0, SEEK_SET) == -1) return NULL;

	char *content = malloc( (size_t) size +1  ); 
	if (content == NULL) return NULL;

	fread(content, 1, (size_t)size, input);
	if (ferror(input)) {
		free(content);
		return NULL;
	}

	fclose(input);
	content[size] = '\0';
	return content;
}

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 {
		fprintf(stderr, "printlog: Not a shader or a program\n");
		return;
	}

	char* log = (char*)malloc(log_length);

	if (glIsShader(object))
		glGetShaderInfoLog(object, log_length, NULL, log);
	else if (glIsProgram(object))
		glGetProgramInfoLog(object, log_length, NULL, log);

	fprintf(stderr, "%s", log);
	free(log);
}

GLuint create_shader(const char* filename, GLenum type)
{
	const GLchar* source = file_read(filename);
	if (source == NULL) {
		fprintf(stderr, "Error opening %s: ", filename); perror("");
		return 0;
	}
	GLuint res = glCreateShader(type);
	glShaderSource(res, 1, &source, NULL);
	free((void*)source);

	glCompileShader(res);
	GLint compile_ok = GL_FALSE;
	glGetShaderiv(res, GL_COMPILE_STATUS, &compile_ok);
	if (compile_ok == GL_FALSE) {
		fprintf(stderr, "%s:", filename);
		print_log(res);
		glDeleteShader(res);
		return 0;
	}

	return res;
}


int main(int argc, char **argv) {
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE);
	glutInitWindowSize(800, 600);
	glutInitContextVersion(3, 3);
	glutInitContextProfile(GLUT_CORE_PROFILE);
	glutCreateWindow("test");
	GLuint vs, fs;
	if ((vs = create_shader("raycast.vert", GL_VERTEX_SHADER))   == 0) return 1;
	if ((fs = create_shader("raycast.frag", GL_FRAGMENT_SHADER)) == 0) return 1;
		/*
		prog <- loadProgram "raycast.vert" "raycast.frag"
		currentProgram $= Just prog
		*/
	GLuint program = glCreateProgram();
	glAttachShader(program, vs);
	glAttachShader(program, fs);
	glLinkProgram(program);
	GLint link_ok = GL_FALSE;
	glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
	if (!link_ok) {
		fprintf(stderr, "glLinkProgram:");
		print_log(program);
	}
	glUseProgram(program);

	glClear(GL_COLOR_BUFFER_BIT);
}