#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>

void usage(void){
	fprintf(stderr, "Usage: rexbacklight [option]\n\n");

	fprintf(stderr, "Options:\n");
	fprintf(stderr, "  =<percentage>\n");
	fprintf(stderr, "  -<percentage>\n");
	fprintf(stderr, "  +<percentage>\n");
	fprintf(stderr, "  off\n");
	fprintf(stderr, "  max\n");
	fprintf(stderr, "  min\n");

	fprintf(stderr, "\nrexbacklight Copyright (C) 2018 rexy712\n");
	fprintf(stderr, "This program comes with ABSOLUTELY NO WARRANTY.\n");
	fprintf(stderr, "This is free software, and you are welcome to redistribute it\n");
	fprintf(stderr, "under certain conditions; see the GNU GPLv3 for details.\n");
	fprintf(stderr, "A copy of the GPLv3 is available with the source in the file 'LICENSE'\n");

	exit(-1);
}

int check_valid_files(const char* f1, const char* f2){
	struct stat file1, file2;
	if(stat(f1, &file1)){
		printf("failed to open '%s'\n", f1);
		return -1;
	}
	if(stat(f2, &file2)){
		printf("failed to open '%s'\n", f2);
		return -1;
	}
	//Same device and same inode means same file

	//device id
	if(file1.st_dev != file2.st_dev)
		return -2;
	//inode number
	if(file1.st_ino != file2.st_ino)
		return -2;
	return 0;
}

int get_brightness(const char* file){
	FILE* bright = fopen(file, "r");
	char buff[127];
	if(!bright){
		fprintf(stderr, "Unable to open brightness file \"%s\"!\n", file);
		return 0;
	}
	if(!fgets(buff, sizeof(buff), bright)){
		fprintf(stderr, "Unable to read file \"%s\"!\n", file);
		fclose(bright);
		return 0;
	}
	fclose(bright);
	return atof(buff);
}

//argv[1] shall be [+-=]<percentage>|min|max|off
int main(int argc, char** argv){
	const char* backlight_file     = "/sys/class/backlight/intel_backlight/brightness";
	const char* max_backlight_file = "/sys/class/backlight/intel_backlight/max_brightness";

	//Make sure we have an argument and it is at least 2 characters long
	if(argc < 2 || strlen(argv[1]) < 2)
		usage();
	else if(!strcmp(argv[1], "--help"))
		usage();

	if(setuid(0)){
		fprintf(stderr, "Unable to setuid to 0!\n");
		return -3;
	}

	if(check_valid_files("/", "/proc/1/root")){
		fprintf(stderr, "No chroot today\n");
		return -4;
	}

	//Min brightness is just 0, so set it up front
	float min_brightness = 0;
	float max_brightness = get_brightness(max_backlight_file);
	float current_brightness = get_brightness(backlight_file);

	//Amount to inc/dec
	int delta;
	if(strlen(argv[1]) > 0)
		delta = max_brightness * atof(argv[1] + 1) / 100.0;
	else
		delta = 0;

	//Open brightness file for writing
	FILE* bright = fopen(backlight_file, "w+");
	if(!bright){
		fprintf(stderr, "Unable to open brightness file \"%s\" for writing!\n", backlight_file);
		return 1;
	}

	//Increment
	if(argv[1][0] == '+'){
		delta = delta + current_brightness;
		if(delta >= max_brightness)
			fprintf(bright, "%d", (int)max_brightness);
		else{
			fprintf(bright, "%d", delta);
		}

	//Decrement
	}else if(argv[1][0] == '-'){
		delta = current_brightness - delta;
		if(delta <= min_brightness)
			fprintf(bright, "%d", (int)min_brightness);
		else
			fprintf(bright, "%d", delta);

	//Directly set
	}else if(argv[1][0] == '='){
		if(delta >= max_brightness)
			fprintf(bright, "%d", (int)max_brightness);
		else if(delta <= min_brightness)
			fprintf(bright, "%d", (int)min_brightness);
		else
			fprintf(bright, "%d", delta);

	//Set to minimum plus one (so backlight is actually on!)
	}else if(!strcmp("min", argv[1])){
		fprintf(bright, "%d", (int)(min_brightness + 1));

	//Turn off backlight
	}else if(!strcmp("off", argv[1])){
		fprintf(bright, "%d", (int)min_brightness);

	//Set to maximum
	}else if(!strcmp("max", argv[1])){
		fprintf(bright, "%d", (int)max_brightness);

	//Unknown option
	}else{
		fclose(bright);
		usage();
	}
	fclose(bright);
	return 0;
}