/*
 * Copyright © 2008, 2017 Nick Bowler
 *
 * License WTFPL2: Do What The Fuck You Want To Public License, version 2.
 * This is free software: you are free to do what the fuck you want to.
 * There is NO WARRANTY, to the extent permitted by law.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <inttypes.h>
#include <xcb/xcb.h>

/* Table of common monitor aspect ratios.  Add to this as necessary. */
static const struct aspect {
	unsigned num, denom;
} aspects[] = {
	{ 16, 10 },
	{ 16, 9 },
	{ 8, 3 },
	{ 5, 4 },
	{ 4, 3 }
};

/*
 * Get the xcb screen structure for the specified screen, or NULL if it doesn't
 * exist.
 */
static xcb_screen_t *getscreen(xcb_connection_t *c, int screen)
{
	xcb_screen_iterator_t iter;

	iter = xcb_setup_roots_iterator(xcb_get_setup(c));
	while (iter.rem) {
		if (screen == 0)
			return iter.data;
		screen--;
		xcb_screen_next(&iter);
	}

	return NULL;
}

void find_nearest_aspect(xcb_screen_t *screen, struct aspect *out)
{
	unsigned int w = screen->width_in_millimeters;
	unsigned int h = screen->height_in_millimeters;

	double r = (double)w/h;
	double d = HUGE_VAL;
	int i;

	for (i = 0; i < (sizeof aspects / sizeof aspects[0]); i++) {
		double t = (double) aspects[i].num / aspects[i].denom;
		double cmp;

		cmp = fabs(r - t);
		if (cmp < d) {
			*out = aspects[i];
			d = cmp;
		}

		cmp = fabs(r - 1/t);
		if (cmp < d) {
			out->num = aspects[i].denom;
			out->denom = aspects[i].num;
			d = cmp;
		}
	}
}

struct options {
	char *displayname;
	int showdimensions;
} *parseoptions(int argc, char **argv)
{
	static struct options opts = { 0 };
	int i;

	for (i = 1; i < argc; i++) {
		if (strcmp(argv[i], "-display") == 0) {
			if (++i < argc) {
				opts.displayname = argv[i];
				continue;
			}
			fprintf(stderr, "-display requires an argument\n");
		} else if (strcmp(argv[i], "-dimensions") == 0) {
			opts.showdimensions = 1;
		}
	}

	return &opts;
}

int main(int argc, char **argv)
{
	struct aspect screenaspect;
	xcb_connection_t *display;
	xcb_screen_t     *screen;
	int screen_num;

	struct options *opts = parseoptions(argc, argv);
	
	display = xcb_connect(opts->displayname, &screen_num);
	if (xcb_connection_has_error(display)) {
		fprintf(stderr, "Failed to open display.\n");
		xcb_disconnect(display);
		return EXIT_FAILURE;
	}

	screen = getscreen(display, screen_num);
	if (!screen) {
		fprintf(stderr, "Invalid screen number.\n");
		xcb_disconnect(display);
		return EXIT_FAILURE;
	}

	if (opts->showdimensions) {
		printf("%" PRIu16 "x%" PRIu16 "-",
		       screen->width_in_pixels, screen->height_in_pixels);
	}

	find_nearest_aspect(screen, &screenaspect);
	printf("%u:%u\n", screenaspect.num, screenaspect.denom);

	xcb_disconnect(display);
	return EXIT_SUCCESS;
}