// SPDX-License-Identifier: GPL-2.0
/*
 * led_hw_brightness_mon.c
 *
 * This program monitors LED brightness level changes having its origin
 * in hardware/firmware, i.e. outside of kernel control.
 * A timestamp and brightness value is printed each time the brightness changes.
 *
 * Usage: led_hw_brightness_mon <device-name>
 *
 * <device-name> is the name of the LED class device to be monitored. Pressing
 * CTRL+C will exit.
 */

#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <linux/uleds.h>

int main(int argc, char const *argv[])
{
        int fd, ret;
        char brightness_file_path[LED_MAX_NAME_SIZE + 11];
        struct pollfd pollfd;
        struct timespec ts;
        char buf[11];

        if (argc != 2) {
                fprintf(stderr, "Requires <device-name> argument\n");
                return 1;
        }

        snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
                 "/sys/class/leds/%s/brightness_hw_changed", argv[1]);

        fd = open(brightness_file_path, O_RDONLY);
        if (fd == -1) {
                printf("Failed to open %s file\n", brightness_file_path);
                return 1;
        }

        /*
         * read may fail if no hw brightness change has occurred so far,
         * but it is required to avoid spurious poll notifications in
         * the opposite case.
         */
        read(fd, buf, sizeof(buf));

        pollfd.fd = fd;
        pollfd.events = POLLPRI;

        while (1) {
                ret = poll(&pollfd, 1, -1);
                if (ret == -1) {
                        printf("Failed to poll %s file (%d)\n",
                                brightness_file_path, ret);
                        ret = 1;
                        break;
                }

                clock_gettime(CLOCK_MONOTONIC, &ts);

                ret = read(fd, buf, sizeof(buf));
                if (ret < 0)
                        break;

                ret = lseek(pollfd.fd, 0, SEEK_SET);
                if (ret < 0) {
                        printf("lseek failed (%d)\n", ret);
                        break;
                }

                printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));
        }

        close(fd);

        return ret;
}