/*
  Copyright (c) 2016, Matthias Schiffer <mschiffer@universe-factory.net>
  All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice,
       this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice,
       this list of conditions and the following disclaimer in the documentation
       and/or other materials provided with the distribution.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/


#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>


#ifndef GLSLWRITE

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

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

#endif


static char *filename;
static float current_time = 0;
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, (unsigned)current_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*(height-1-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);

#ifndef GLSLWRITE
	unsigned ticks = SDL_GetTicks();
	current_time += speed * (ticks - previous_ticks);
	previous_ticks = ticks;
#endif

	glUniform1f(time_loc, current_time);
	glUniform2f(res_loc, width, height);

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

#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 '=':
			if (speed < 0)
				speed = -1.0;
			else
				speed = 1.0;
			break;

		case '<':
			if (speed > 0)
				speed = -speed;
			break;

		case '>':
			if (speed < 0)
				speed = -speed;
		}
	}
}
#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("glslview", 0, 0, 400, 400, 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]);
		current_time += 20;
#endif
	}

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

	return 0;
}