/* SPDX-License-Identifier: ISC */
/*
 * shadermeh.c
 *
 * Copyright (C) 2022 David Oberhollenzer <goliath@infraroot.at>
 */
#include "shadermeh.h"

static GLfloat vertex_buffer[] = {
	-1.0f, -1.0f, 0.0f,	/* lower left corner */
	 1.0f,  1.0f, 1.0f,

	+1.0f, -1.0f, 0.0f,	/* lower right corner */
	 1.0f,  1.0f, 1.0f,

	-1.0f,  1.0f, 0.0f,	/* uper left corner */
	 1.0f,  1.0f, 1.0f,

	+1.0f, +1.0f, 0.0f,	/* upper right corner */
	 1.0f,  1.0f, 1.0f,
};

static double diff_timespec(const struct timespec *time1,
			    const struct timespec *time0)
{
	return (time1->tv_sec - time0->tv_sec)
		+ (time1->tv_nsec - time0->tv_nsec) / 1000000000.0;
}

static void convert_for_ffmpeg(const uint8_t *in, uint8_t *out,
			       size_t width, size_t height)
{
	size_t x, y;

	for (y = 0; y < height; ++y) {
		const uint8_t *src = in + y * width * 4;
		uint8_t *dst = out + (height - 1 - y) * width * 3;

		for (x = 0; x < width; ++x) {
			*(dst++) = *(src++);
			*(dst++) = *(src++);
			*(dst++) = *(src++);
			++src;
		}
	}
}

static int write_retry(int fd, const void *buffer, size_t size)
{
	while (size > 0) {
		int ret = write(fd, buffer, size);

		if (ret < 0) {
			if (errno == EINTR)
				continue;
			perror("write");
			return -1;
		}

		if (ret == 0)
			return -1;

		size -= ret;
		buffer = (const char *)buffer + ret;
	}

	return 0;
}

static const struct option long_opts[] = {
	{ "width", required_argument, NULL, 'w' },
 	{ "height", required_argument, NULL, 'h' },
	{ "shader", required_argument, NULL, 's' },
	{ "to-stdout", no_argument, NULL, 'S' },
	{ NULL, 0, NULL, 0 },
};

static const char *short_opts = "w:h:s:S";

static const char *usage_str =
"shadermeh OPTIONS...\n"
"\n"
"Possible options:\n"
"\n"
"  --width, -w <pixels>\n"
"  --height, -h <pixels>\n"
"\n"
"  --to-stdout, -S\n"
"\n"
"  --shader, -s <shader file>\n"
"\n";

int main(int argc, char **argv)
{
	GLuint u_iResolution, u_iTime, u_iTimeDelta, u_iFrame;
	struct timespec start, frame_start, frame_end;
	unsigned int width, height, iFrame = 0;
	void *fb32 = NULL, *fb24 = NULL;
	const char *shader_file = NULL;
	GLuint vao, vbo, fbo, fbo_tex;
	GLint major, minor, prog;
	float iTime, iTimeDelta;
	bool to_stdout = false;
	window *wnd;
	int i;

	/******************** parse options ************************/
	width = 800;
	height = 450;

	for (;;) {
		i = getopt_long(argc, argv, short_opts, long_opts, NULL);
		if (i == -1)
			break;

		switch (i) {
		case 'w':
			width = strtol(optarg, NULL, 10);
			break;
		case 'h':
			height = strtol(optarg, NULL, 10);
			break;
		case 's':
			shader_file = optarg;
			break;
		case 'S':
			to_stdout = true;
			break;
		default:
			fputs(usage_str, stderr);
			return EXIT_FAILURE;
		}
	}

	if (!shader_file) {
		fputs(usage_str, stderr);
		fputs("No shader file specified!\n", stderr);
		return EXIT_FAILURE;
	}

	if (to_stdout) {
		fb32 = calloc(1, width * height * 4);
		if (!fb32) {
			perror("allocating scratch framebuffer");
			return EXIT_FAILURE;
		}

		fb24 = calloc(1, width * height * 3);
		if (!fb24) {
			perror("allocating scratch framebuffer");
			free(fb32);
			return EXIT_FAILURE;
		}
	}

	/********** create window and make context current **********/
	wnd = window_create(width, height, "shader meh...");

	if (!wnd) {
		fputs("failed to create window", stderr);
		free(fb32);
		free(fb24);
		return EXIT_FAILURE;
	}

	window_make_current(wnd);
	window_set_vsync(wnd, 1);

	/******************** load entry points ********************/
	glewExperimental = GL_TRUE;

	if (glewInit() != GLEW_OK) {
		fputs("glewInit() error", stderr);
		window_destroy(wnd);
		free(fb32);
		free(fb24);
		return EXIT_FAILURE;
	}

	glGetIntegerv(GL_MAJOR_VERSION, &major);
	glGetIntegerv(GL_MINOR_VERSION, &minor);

	if (!to_stdout)
		printf("OpenGL version %d.%d\n", major, minor);

	/******************** initialization ********************/
	glViewport(0, 0, width, height);
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

	/* vertex buffer object & vertex array object */
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	glGenBuffers(1, &vbo);
	glBindBuffer(GL_ARRAY_BUFFER, vbo);

	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer),
		     vertex_buffer, GL_STATIC_DRAW);

	glEnableVertexAttribArray(0);
	glEnableVertexAttribArray(1);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 6, 0);
	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 6,
			      (GLvoid *)(3 * sizeof(GLfloat)));

	/* shader */
	prog = shader_program_load(shader_file);

	if (!shader_program_get_build_status(prog)) {
		shader_program_print_info_log(prog);
		goto fail_vao;
	}

	glUseProgram(prog);

	/* uniforms */
	u_iResolution = glGetUniformLocation(prog, "iResolution");
	u_iTime = glGetUniformLocation(prog, "iTime");
	u_iTimeDelta = glGetUniformLocation(prog, "iTimeDelta");
	u_iFrame = glGetUniformLocation(prog, "iFrame;");

	glUniform3f(u_iResolution, width, height, 0.0f);

	clock_gettime(CLOCK_MONOTONIC_RAW, &start);

	/******************** framebuffer object ********************/
	if (to_stdout) {
		glGenFramebuffers(1, &fbo);
		glGenTextures(1, &fbo_tex);

		glBindTexture(GL_TEXTURE_2D, fbo_tex);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0,
			     GL_RGBA, GL_UNSIGNED_BYTE, NULL);
		glBindTexture(GL_TEXTURE_2D, 0);

		glBindFramebuffer(GL_FRAMEBUFFER, fbo);
		glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
				     fbo_tex, 0);

		glBindFramebuffer(GL_FRAMEBUFFER, 0);
	} else {
		window_show(wnd);
	}

	/******************** drawing loop ********************/
	while (to_stdout || window_handle_events()) {
		/* render image to FBO */
		clock_gettime(CLOCK_MONOTONIC_RAW, &frame_start);

		if (to_stdout)
			glBindFramebuffer(GL_FRAMEBUFFER, fbo);

		glClear(GL_COLOR_BUFFER_BIT);
		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

		if (to_stdout) {
			glFlush();
		} else {
			window_swap_buffers(wnd);
		}

		/* get image from FBO, dump to stdout */
		if (to_stdout) {
			glBindFramebuffer(GL_FRAMEBUFFER, 0);
			glBindTexture(GL_TEXTURE_2D, fbo_tex);

			glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA,
				      GL_UNSIGNED_BYTE, fb32);

			glBindTexture(GL_TEXTURE_2D, 0);

			convert_for_ffmpeg(fb32, fb24, width, height);

			if (write_retry(STDOUT_FILENO, fb24,
					width * height * 3)) {
				break;
			}
		}

		/* update timers */
		clock_gettime(CLOCK_MONOTONIC_RAW, &frame_end);

		iFrame += 1;
		iTimeDelta = diff_timespec(&frame_end, &frame_start);
		iTime = diff_timespec(&frame_end, &start);

		glUniform1f(u_iTimeDelta, iTimeDelta);
		glUniform1f(u_iTime, iTime);
		glUniform1ui(u_iFrame, iFrame);
	}

	/******************** cleanup ********************/
	if (to_stdout) {
		glBindFramebuffer(GL_FRAMEBUFFER, 0);
		glDeleteFramebuffers(1, &fbo);
		glDeleteTextures(1, &fbo_tex);
	}

	glUseProgram(0);
	glDeleteProgram(prog);
fail_vao:
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glDeleteBuffers(1, &vbo);
	glBindVertexArray(0);
	glDeleteVertexArrays(1, &vao);

	window_make_current(NULL);
	free(fb32);
	free(fb24);
	window_destroy(wnd);
	return EXIT_SUCCESS;
}