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

#include <X11/extensions/scrnsaver.h>

#define TEMP_FILE "/tmp/caffeine"

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

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 = 1;
    errno = save_errno;
}

void termhdl(int sig)
{
    int save_errno = errno;
    signal(SIGTERM, termhdl);
    n = 2;
    errno = save_errno;
}
#endif

int main(int argc, char *argv[])
{
    Display *dpy;
    int event_base, error_base, major, minor;
    int is_on;

    /*daemonize();*/

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

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

    dpy = XOpenDisplay(0);
    if(!dpy) {
        syslog(LOG_ERR, "Failed to open display.");
        return 1;
    }

    if(!XScreenSaverQueryExtension(dpy, &event_base, &error_base)) {
        syslog(LOG_ERR, "XScreenSaver extension does not exist.");
        return 2;
    }

    XScreenSaverQueryVersion(dpy, &major, &minor);
    if(!(major > 1 || (major == 1 && minor >= 1))) {
        syslog(LOG_ERR, "XScreenSaver extension is too old, need >=1.1.");
        return 3;
    }

    is_on = 0;
    for(;;) {
        pause();
        if(n == 0) {
            /* do nothing */
        } else if(n == 1) {
            is_on = !is_on;
            if(is_on) {
                syslog(LOG_INFO, "Enabling...");
                creat(TEMP_FILE, 0644);
                XScreenSaverSuspend(dpy, True);
            } else {
                syslog(LOG_INFO, "Disabling...");
                unlink(TEMP_FILE);
                XScreenSaverSuspend(dpy, False);
            }
            XSync(dpy, False);
        } else if(n == 2) {
            syslog(LOG_INFO, "Shutting down...");
            unlink(TEMP_FILE);
            XScreenSaverSuspend(dpy, False);
            XSync(dpy, False);
            break;
        } else {
            /* unknown state */
        }

        n = 0;
    }

    closelog();

    return 0;
}