#include <unistd.h> /* access */
#include <stdlib.h> /* exit */
#include <syslog.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
#include <string.h> /* strcmp */

/* Kernel module entry for the Apple Human Interface Device driver. */
#define APPLE_HID_PATH "/sys/module/hid_apple"

char file_exists(const char *filename)
{
    return access(filename, F_OK) != -1;
}

int init_apple_hid_module()
{
    int fd;

    if(!file_exists(APPLE_HID_PATH)) {
        syslog(LOG_WARNING, "Apple hid module is unloaded.");
        return -1;
    }

    fd = open(APPLE_HID_PATH"/parameters/fnmode", O_RDWR);
    if(fd == -1) {
        syslog(LOG_WARNING, "Failed to open %s.",
               APPLE_HID_PATH"/parameters/fnmode");
        return -1;
    }

    return fd;
}

int get_fn_lock()
{
    int fd;
    char state;

    fd = init_apple_hid_module();
    if(fd != -1) {
        if(read(fd, &state, 1) != 1)
            state = '0';
        close(fd);
    }

    return state == '2';
}

void set_fn_lock_on()
{
    int fd;

    fd = init_apple_hid_module();
    if(fd != -1) {
        if(write(fd, "2", 1) != 1)
            syslog(LOG_WARNING, "Failed to write to Apple HID driver.");
        else
            syslog(LOG_INFO, "Fn lock is on.");
        close(fd);
    }
}

void set_fn_lock_off()
{
    int fd = init_apple_hid_module();
    if(fd != -1) {
        if(write(fd, "1", 1) != 1)
            syslog(LOG_WARNING, "Failed to write Apple HID driver.");
        else
            syslog(LOG_INFO, "Fn lock is off.");
        close(fd);
    }
}

void daemonize()
{
    close(0);
    close(1);
    close(2);
    open("/dev/null", O_RDONLY); /* stdin */
    open("/dev/null", O_WRONLY); /* stdout */
    open("/dev/null", O_WRONLY); /* stderr */
    chdir("/");
    int pid = fork();
    if(pid > 0)
        exit(0);
    setsid();
    pid = fork();
    if(pid > 0)
        exit(0);
}

#if 1
static volatile sig_atomic_t n = 0;

void usr1hdl(int sig)
{
    int save_errno = errno;
    signal(SIGUSR1, usr1hdl);
    n = 0;
    errno = save_errno;
}

void termhdl(int sig)
{
    int save_errno = errno;
    signal(SIGTERM, termhdl);
    n = 1;
    errno = save_errno;
}
#endif

int main(int argc, char *argv[])
{
    /*daemonize();*/

    signal(SIGUSR1, usr1hdl);
    signal(SIGTERM, termhdl);

    openlog("hid_apple_fn_lock", 0, LOG_USER);
    syslog(LOG_INFO, "Daemon started, pid == %d", getpid());

    uid_t euid = geteuid();
    if(euid != 0) {
        syslog(LOG_WARNING, "Must have root priviliges. Quitting...");
        return 1;
    }

    for(;;) {
        pause();
        if(n == 0) {
            if(get_fn_lock())
                set_fn_lock_off();
            else
                set_fn_lock_on();
        } else if(n == 1) {
            syslog(LOG_INFO, "Shutting down...");
            break;
        } else {
            /* ignore */
        }
    }

    closelog();

    return 0;
}