#define _DEFAULT_SOURCE
#define _POSIX_C_SOURCE 200809L
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <stdarg.h>
#include <errno.h>
#include <string.h>
#include <wordexp.h>
#include <limits.h>
#include <getopt.h>
#include <unistd.h>

#define BACKLIGHT_ROOT_PATH "/sys/class/backlight/"
#define BL_MIN 5

#define const_arr_size(val) ((int)(sizeof(val)/sizeof(val[0])))

const char *savefile_paths[] = {
	NULL, /* reserved for external savefile path */
	"/etc/sblsave"
};

enum action {
	DISPLAY, INCREASE, DECREASE, SET, RESTORE
};

static uid_t ruid;
static int device_index = 0;
static const char *savefile;
static int max_brightness;
static const char *device_path;

static void die (const char *, ...);
static void usage (void);
static void list_cards (void);
static void set_brightness (float);
static void change_permissions (const char *);
static void restore_permissions (void);
static int save_value (float);
static int get_max_brightness (void);
static float get_saved_value (void);
static float get_current_brightness (void);
static const char * get_device_path (int);
static const char * get_savefile (void);

int main (int argc, char *argv[])
{
	int opc = 0, store = 0;
	enum action act = DISPLAY;
	float value = BL_MIN;
	char *extfile = NULL;
	/* Parse command line arguments */
	while ((opc = getopt(argc, argv, "c:hI:li:d:s:Sr")) != -1) {
		switch (opc) {
		case 'l':
			list_cards();
			break;
		case 'h':
			usage();
			break;
		case 'c':
			extfile = malloc(strlen(optarg) + 1);
			if (!extfile)
				die("malloc in main():");
			strcpy(extfile, optarg);
			savefile_paths[0] = extfile;
			break;
		case 'I':
			device_index = atoi(optarg);
			break;
		case 'i':
			act = INCREASE;
			value = atof(optarg);
			break;
		case 'd':
			act = DECREASE;
			value = atof(optarg);
			break;
		case 's':
			act = SET;
			value = atof(optarg);
			break;
		case 'r': 
			act = RESTORE;
			break;
		case 'S':
			store = 1;
			break;
		default:
			exit(EXIT_FAILURE);
			break;
		}
	}

	ruid = getuid ();
	if (!(device_path = get_device_path(device_index)))
		die("invalid device index");
	max_brightness = get_max_brightness();
	savefile = get_savefile();
	
	switch (act) {
		case DISPLAY:
			printf("%.2f\n", get_current_brightness());
			break;
		case SET:
			set_brightness(value);
			break;
		case INCREASE:
			value += get_current_brightness();
			set_brightness(value);
			break;
		case DECREASE:
			value = get_current_brightness() - value;
			set_brightness(value);
			break;
		case RESTORE:
			set_brightness(get_saved_value());
			break;
		default:
			break;
	}

	if (store)
		save_value(get_current_brightness());

	if (extfile)
		free(extfile);
	return 0;
}

int save_value (float value)
{
	FILE *fd;
	change_permissions(savefile);
	fd = fopen(savefile, "w");
	if (!fd)
		die("could not open savefile");
	fprintf(fd, "%f\n", value);
	fclose(fd);
	restore_permissions();
	return 1;
}

float get_saved_value (void)
{
	FILE *fd;
	float rtf = -1;
	fd = fopen(savefile, "r");
	if (!fd)
		die("could not open savefile");
	fscanf(fd, "%f", &rtf);
	fclose(fd);
	return rtf;
}

float get_current_brightness (void)
{
	FILE *fd;
	char buf[PATH_MAX] = {0};
	int cb = -1;
	strcpy(buf, device_path);
	strcat(buf, "/brightness");
	fd = fopen(buf, "r");
	if (!fd)
		die("could not open %s", buf);
	fscanf(fd, "%d", &cb);
	fclose(fd);
 
	return ((float)cb / (float)max_brightness) * 100.0;;
}

int get_max_brightness (void)
{
	FILE *fd;
	char buf[PATH_MAX] = {0};
	int rti = -1;
	strcpy(buf, device_path);
	strcat(buf, "/max_brightness");
	fd = fopen(buf, "r");
	if (!fd)
		die("could not open %s", buf);
	fscanf(fd, "%d", &rti);
	fclose(fd);

	return rti;
}

/* Return the correct savefile path, creating it if it does not exist */
const char * get_savefile (void)
{
	static char buf[PATH_MAX];
	wordexp_t result = {0};
	FILE *fd;

	for (int i = 0; i < const_arr_size(savefile_paths); i++) {
		if (!savefile_paths[i])
			continue;
		switch (wordexp(savefile_paths[i], &result, 0)) {
		case 0:
			break;
		case WRDE_NOSPACE:
			wordfree (&result);
			die("Not enough space");
		default:
			die("Path not valid");
		}

		strcpy(buf, result.we_wordv[0]);
		if ((fd = fopen(result.we_wordv[0], "r")))
			break;
	}
	/* Create a savefile */
	if (!fd) {
		wordfree(&result);
		for (int i = 0; i < const_arr_size(savefile_paths); i++) {
			if (!savefile_paths[i])
				continue;
			switch (wordexp(savefile_paths[i], &result, 0)) {
			case 0:
				break;
			case WRDE_NOSPACE:
				wordfree (&result);
				die("Not enough space");
			default:
				die("Path not valid");
			}

			strcpy(buf, result.we_wordv[0]);
			change_permissions(buf);
			if ((fd = fopen(result.we_wordv[0], "w")))
				break;
		}
	}
	restore_permissions();
	wordfree(&result);
	if (!fd)
		die("could not open or create a savefile");
	fclose(fd);
	return buf;
}	

const char * get_device_path (int index)
{
	DIR *dp;
	struct dirent *de;
	static char buf[PATH_MAX];

	memset(buf, 0, PATH_MAX);
	if (index < 0)
		die("%d is not a valid index", index);
	if (!(dp = opendir(BACKLIGHT_ROOT_PATH)))
		die("error opening " BACKLIGHT_ROOT_PATH);

	errno = 0;
	while ((de = readdir(dp))) {
		if (!(de->d_type & DT_LNK))
			continue;
		if (index) {
			index--;
			continue;
		} else {
			strcpy(buf, BACKLIGHT_ROOT_PATH);
			strcat(buf, de->d_name);
			break;
		}
	}
	closedir(dp);
	if (errno)
		die("error reading " BACKLIGHT_ROOT_PATH);
	// FIXME: actually check return value of this
	if (!buf[0])
		return NULL;
	return buf;

}

void list_cards (void)
{
	int i = 0;
	const char *s;
	for (; (s = get_device_path(i)); i++)
		printf("%d: %s\n", i, s);
	exit(EXIT_SUCCESS);
}

void set_brightness (float value)
{
	int set;
	char buf[PATH_MAX] = {0};
	FILE *fd;
	if (value > 100)
		value = 100;
	if (value < BL_MIN)
		value = BL_MIN;
	set = (value/100.0) * max_brightness;
	if (set < 0)
		return; 
	strcpy(buf, device_path);
	strcat(buf, "/brightness");
	change_permissions(buf);
	fd = fopen(buf, "w");
	if (!fd)
		die("could not open %s", buf);
	fprintf(fd, "%d", set);
	fclose(fd);
	restore_permissions();
}

/* Change the process permissions matching the ones pointed by path */
void change_permissions (const char *path)
{
	int status;
	struct stat st;
	static char buf[PATH_MAX];
	char *p;

	if (stat(path, &st) == -1) {
		if (errno != ENOENT)
			die("stat error");
		strcpy(buf, path);
		for (p = &buf[strlen(buf) - 1]; *p && p != buf; p--) {
			if (*p == '/') {
				*p = '\0';
				if (stat(buf, &st) != -1)
					break;
			}
		}
		if (p == buf)
			die("stat error, invalid path");
	}
	status = seteuid(st.st_uid);
	if (status < 0)
		die("could not setuid");
}

static void restore_permissions (void)
{
	int status;
	status = seteuid(ruid);
	if (status < 0)
		die("could not setuid");
}

void die(const char *fmt, ...)
{
	va_list ap;
	va_start(ap, fmt);

     	vfprintf(stderr, fmt, ap);

	if (fmt[0] && fmt[strlen(fmt) - 1] == ':') {
		fputc(' ', stderr);
		perror(NULL);
	} else {
		fputc('\n', stderr);
	}

	va_end(ap);
	exit(errno ? errno : 1);
}

static void usage (void)
{
	puts("Usage: sbl [-hlrS] [-c savefile] [-I index] [-i/d/s percent]\n"
	     "-h              print this message\n"
	     "-l              list devices by index\n"
	     "-r              restore saved value\n"
	     "-S              save value\n"
	     "-c savefile     specify savefile\n"
	     "-I index        specify device by index\n"
	     "-i percent      increase backlight by percent\n"
     	     "-d percent      decrease backlight by percent\n"
	     "-s percent      set backlight to percent\n");
	exit(EXIT_SUCCESS);
}