#include <stdio.h>
#include <stdlib.h>

#define ROOT_DIR "/sys/class/backlight/intel_backlight/"
#define BRIGHTNESS_STEP 750


int main(int argc, char** argv) {
	FILE* brightness = fopen(ROOT_DIR "brightness", "r+");
	if(brightness == NULL) {
		perror("fopen");
		exit(EXIT_FAILURE);
	}

	int current_brightness;

	int res = fscanf(brightness, "%d", &current_brightness);
	if(res != 1) {
		perror("fscanf");
		exit(EXIT_FAILURE);
	}


	if(argc != 2) {
		fprintf(stderr, "Exactly one argument is required. Got %d arguments.\n", argc);
		exit(EXIT_FAILURE);
	}

	if(*argv[1] == '+') {
		current_brightness+=BRIGHTNESS_STEP;
	} else if(*argv[1] == '-') {
		current_brightness-=BRIGHTNESS_STEP;
	} else {
		fprintf(stderr, "Argument must be '+' or '-', got %s.\n", argv[1]);
		exit(EXIT_FAILURE);
	}

	if(current_brightness < 0)
		current_brightness = 0;

	rewind(brightness);

	if(!fprintf(brightness, "%d", current_brightness)) {
		perror("fprintf");
		exit(EXIT_FAILURE);
	}


	if(fclose(brightness)) {
		perror("fclose");
		exit(EXIT_FAILURE);
	}

	return 0;

}