#include <fcntl.h>
#include <limits.h>
#include <math.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <unistd.h>

#ifdef USE_INOTIFY
# include <sys/inotify.h>
# include <sys/stat.h>
# include <sys/types.h>
#endif

#ifdef GLSLWRITE
# include <png.h>
#endif

#include <GL/glew.h>

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>


#ifdef GLSLWRITE

static unsigned frame_time = 0;

#else

static float speed = 1.0;
static float current_time = 0;
static unsigned previous_ticks = 0;

#ifdef USE_INOTIFY
static int inotify_fd = -1;
static int inotify_watch = -1;
#endif

#endif


static char *filename;
static GLint time_loc;
static GLint res_loc;


static char * readfile(const char *name) {
	FILE *f = fopen(name, "r");
	if (!f)
		return NULL;

	size_t size = 1024;
	char *buffer = malloc(size+1);
	size_t count = 0, r;

	do {
		if (count == size) {
			size *= 2;
			buffer = realloc(buffer, size+1);
		}

		r = fread(buffer+count, 1, size-count, f);
		count += r;
	} while (r);

	fclose(f);

	buffer[count] = 0;

	return buffer;
}

static void printShaderInfoLog(GLuint obj) {
	GLint length = 0;

	glGetShaderiv(obj, GL_INFO_LOG_LENGTH, &length);

	if(length > 0) {
		char log[length];

		glGetShaderInfoLog(obj, sizeof(log), NULL, log);
		fprintf(stderr, "%s\n", log);
	}
}

static void printProgramInfoLog(GLuint obj) {
	GLint length = 0;

	glGetProgramiv(obj, GL_INFO_LOG_LENGTH, &length);

	if(length > 0) {
		char log[length];

		glGetProgramInfoLog(obj, sizeof(log), NULL, log);
		fprintf(stderr, "%s\n", log);
	}
}

static void load(void) {
	char *shader = readfile(filename);
	if (!shader) {
		fprintf(stderr, "Error: unable to read '%s'\n", filename);
		return;
	}

	GLuint frag = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(frag, 1, (const GLchar **)&shader, NULL);
	glCompileShader(frag);
	printShaderInfoLog(frag);

	GLuint program = glCreateProgram();
	glAttachShader(program, frag);

	glLinkProgram(program);
	printProgramInfoLog(program);

	glBindFragDataLocation(program, 0, "fragColor");
	time_loc = glGetUniformLocation(program, "time");
	res_loc = glGetUniformLocation(program, "res");

	glUseProgram(program);

	free(shader);
	glDeleteShader(frag);
	glDeleteProgram(program);
}

#if defined(USE_INOTIFY) && !defined(GLSLWRITE)
static void reset_watch(void) {
	if (inotify_watch >= 0) {
		if (inotify_rm_watch(inotify_fd, inotify_watch)) {
			fprintf(stderr, "unable to remove watch\n");
			exit(1);
		}
	}

	inotify_watch = inotify_add_watch(inotify_fd, filename, IN_CLOSE_WRITE);
	if (inotify_watch < 0) {
		fprintf(stderr, "unable to watch '%s' for changes\n", filename);
		return;
	}
}
#endif

static void init(void) {
#if defined(USE_INOTIFY) && !defined(GLSLWRITE)
	inotify_fd = inotify_init();
	if (inotify_fd < 0) {
		fprintf(stderr, "unable to initialize inotify\n");
		exit(1);
	}

	fcntl(inotify_fd, F_SETFL, fcntl(inotify_fd, F_GETFL)|O_NONBLOCK);

	reset_watch();
#endif

	glewInit();
	glDisable(GL_DEPTH_TEST);
	glColor4f(0, 0, 0, 0);

	load();
}

static void check_reload(void) {
#if defined(USE_INOTIFY) && !defined(GLSLWRITE)
	char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
	if (read(inotify_fd, buf, sizeof(buf)) > 0)
		load();
#endif
}

#ifdef GLSLWRITE
static void savePNG(int width, int height, const char *output_dir) {
	uint8_t pixels[width*height*4];
	glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8, pixels);

	char filename[strlen(output_dir) + 20];
	snprintf(filename, sizeof(filename), "%s/%010u.png", output_dir, frame_time);

	FILE *f = fopen(filename, "wb");
	if (!f) {
		fprintf(stderr, "unable to open PNG file\n");
		exit(1);
	}

	png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
	if (!png_ptr) {
		fprintf(stderr, "unable to open PNG file\n");
		exit(1);
	}

	png_set_swap_alpha(png_ptr);

	png_infop info_ptr = png_create_info_struct(png_ptr);
	if (!info_ptr) {
		fprintf(stderr, "unable to create PNG info struct\n");
		exit(1);
	}

	if (setjmp(png_jmpbuf(png_ptr))) {
		fprintf(stderr, "unable to write PNG file\n");
		exit(1);
	}

	png_init_io(png_ptr, f);

	png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_RGB_ALPHA,
		     PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);

	uint8_t *row_pointers[height];
	for (size_t i = 0; i < height; i++)
		row_pointers[i] = &pixels[4*i*width];

	png_set_rows(png_ptr, info_ptr, row_pointers);
	png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

	png_destroy_write_struct(&png_ptr, &info_ptr);
	fclose(f);
}
#endif

static void render(int width, int height) {
	glViewport(0, 0, (GLsizei)width, (GLsizei)height);

#ifdef GLSLWRITE

	glUniform1f(time_loc, frame_time);

#else

	unsigned ticks = SDL_GetTicks();
	current_time += speed * (ticks - previous_ticks);
	previous_ticks = ticks;

	glUniform1f(time_loc, current_time);

#endif

	glUniform2f(res_loc, width, height);

	glBegin(GL_QUADS);
	glVertex2f(-1, -1);
	glVertex2f(1, -1);
	glVertex2f(1, 1);
	glVertex2f(-1, 1);
	glEnd();

#ifdef GLSLWRITE
	frame_time += 20;
#endif
}

#ifndef GLSLWRITE
static void handle_input(const char *input) {
	for (; *input; input++) {
		switch (*input) {
		case 'l':
#ifdef USE_INOTIFY
			reset_watch();
#endif
			load();
			break;

		case 'r':
			current_time = 0;
			break;

		case '+':
			speed *= 1.1;
			break;

		case '-':
			speed /= 1.1;
			break;

		case '=':
			speed = 1.0;
		}
	}
}
#endif

int main(int argc, char *argv[]) {
#ifdef GLSLWRITE
	if (argc != 3) {
		fprintf(stderr, "Usage: glslwrite <shader> <output directory>\n");
		exit(1);
	}
#else
	if (argc != 2) {
		fprintf(stderr, "Usage: glslview <shader>\n");
		exit(1);
	}
#endif

	SDL_Init(SDL_INIT_VIDEO);

	SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);

	SDL_Window *window = SDL_CreateWindow("glslwrite", 0, 0, 800, 800, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
	SDL_GLContext ctx = SDL_GL_CreateContext(window);

	filename = argv[1];
	init();

	SDL_StartTextInput();

	while (true) {
		SDL_Event e;

		while (SDL_PollEvent(&e)) {
			switch (e.type) {
			case SDL_KEYDOWN:
				switch (e.key.keysym.sym) {
				case SDLK_ESCAPE:
					goto quit;
				}
				break;

#ifndef GLSLWRITE
			case SDL_TEXTINPUT:
				handle_input(e.text.text);
				break;

			case SDL_MOUSEWHEEL:
				speed /= pow(1.1, e.wheel.y);
				break;
#endif

			case SDL_QUIT:
				goto quit;
			}
		}

		check_reload();

		int width, height;
		SDL_GetWindowSize(window, &width, &height);

		render(width, height);
		SDL_GL_SwapWindow(window);

#ifdef GLSLWRITE
		savePNG(width, height, argv[2]);
#endif
	}

 quit:
	SDL_StopTextInput();
	SDL_GL_DeleteContext(ctx);
	SDL_DestroyWindow(window);
	SDL_Quit();

	return 0;
}