// WTFPL

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/param.h>

#define MS  * 1000
#define SEC * 1000000

#define DEBOUNCE (10 MS)
#define THREAD_WAIT (100 MS)
#define BACKLIGHT_TIME (10 SEC)
#define BACKLIGHT_FADE_FRAMETIME (50 MS)
#define BACKLIGHT_FADE_TIME (1000 MS)
#define BACKLIGHT_FADE_STEPS (BACKLIGHT_FADE_TIME / BACKLIGHT_FADE_FRAMETIME)

#define KEYPRESS_SIZE 72
#define KEYBOARD_FILE "/dev/input/event1"
#define BACKLIGHT_FILE "/sys/class/leds/keyboard_light/brightness"

//#define BACKLIGHT_FILE stdout

#define MAX_BRIGHTNESS 255

static struct timeval* last_press;
static uint32_t curr_brightness;
static FILE* backlight_fp;

void write_to_backlight(int n) {
	fprintf(backlight_fp, "%d", n);
	fflush(backlight_fp);

	curr_brightness = n;
}

#if 0
void backlight_fade(void) {
	short brightness_step = MAX_BRIGHTNESS / BACKLIGHT_FADE_STEPS;
	short* brightness = malloc(sizeof(short));

	*brightness = MAX_BRIGHTNESS;

	fprintf(stderr, "ha, gay\n");

	do {
		fprintf(stderr, "%d %d %d\n", *brightness, brightness_step, 0);

		write_to_backlight(*brightness);
		*brightness -= brightness_step;

		usleep(BACKLIGHT_FADE_FRAMETIME);
	} while (*brightness >= brightness_step);
}
#endif

void backlight_off(void) {
	if (curr_brightness == 0) return;
	write_to_backlight(0);

//	backlight_fade();
}

void backlight_on(void) {
	curr_brightness = MAX_BRIGHTNESS;

	write_to_backlight(MAX_BRIGHTNESS);
	usleep(BACKLIGHT_TIME);
}

void light_thread(void) {
	// check last_press vs time, do the thing
	backlight_fp = fopen(BACKLIGHT_FILE, "w");

//	FILE* backlight_fp = BACKLIGHT_FILE;

	struct timeval now;

	uint64_t now_usec;
	uint64_t press_usec;
	uint64_t diff;

	while (1) {
		gettimeofday(&now, NULL);

		now_usec = now.tv_sec * 1000000L;
		now_usec += now.tv_usec;

		press_usec = last_press->tv_sec * 1000000L;
		press_usec += last_press->tv_usec;

		diff = now_usec - press_usec;

		if (diff > BACKLIGHT_TIME)	backlight_off();
		else						backlight_on();

		usleep(THREAD_WAIT);

		fflush(stdout);
	}
}

void on_press(void) {
	gettimeofday(last_press, NULL);
}

void daemonize(void) {
	daemon(0, 0);
}

int main(int argc, const char* argv[]) {
	FILE* fp = fopen(KEYBOARD_FILE, "r");
	fseek(fp, 0, SEEK_END);

	void* discard = malloc(KEYPRESS_SIZE);

	// shared mem b/c new proc doesn't share mem space
	last_press = mmap(NULL, sizeof(last_press), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);

	if (fork() == 0) {
		daemonize();
		light_thread();
	} else daemonize();

	while (1) {
		fseek(fp, 0, SEEK_END);
		fread(discard, 1, KEYPRESS_SIZE, fp);

		on_press();

		usleep(DEBOUNCE);
	}

	return 0;
}