#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/select.h>
#include <errno.h>

#define DEVICE_PATH "/dev/power"
#define BUFFER_SIZE 256

int main() {
    int fd;
    fd_set read_fds;
    struct timeval timeout;
    char buffer[BUFFER_SIZE];
    int ret;

    fd = open(DEVICE_PATH, O_RDONLY | O_NONBLOCK);
    if (fd < 0) {
        perror("open device failed");
        return EXIT_FAILURE;
    }

    printf("Waiting for data from %s (select mode)...\n", DEVICE_PATH);

    while (1) {
        FD_ZERO(&read_fds);
        FD_SET(fd, &read_fds);

        timeout.tv_sec = 5;
        timeout.tv_usec = 0;

        ret = select(fd + 1, &read_fds, NULL, NULL, &timeout);

        if (ret < 0) {
            perror("select error");
            close(fd);
            return EXIT_FAILURE;
        } else if (ret == 0) {
            printf("select timeout after 5 seconds, continue waiting...\n");
            continue;
        }

        if (FD_ISSET(fd, &read_fds)) {
            memset(buffer, 0, BUFFER_SIZE);
            ret = read(fd, buffer, BUFFER_SIZE - 1);
            if (ret < 0) {
                if (errno != EAGAIN) {
                    perror("read error");
                }
                continue;
            } else if (ret == 0) {
                printf("device closed? ret=0\n");
                break;
            } else {
                printf("Received %d bytes: %s\n", ret, buffer);
                if (strstr(buffer, "battery") != NULL) {
                    printf("  -> Battery related data\n");
                }
            }
        }
    }

    close(fd);
    return EXIT_SUCCESS;
}