/* need this, or else we don't get a prototype for strdup() from string.h */
#define _POSIX_C_SOURCE 200809L

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <linux/joystick.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <limits.h>
#include <errno.h>

#ifdef HAVE_X11
#  include <X11/Xlib.h>
#endif

#ifndef PATH_MAX
#  define PATH_MAX 1024
#endif

/* -c option: */
const char *command = "xscreensaver-command -deactivate";
/* -i option: */
int interval = 60;
/* cleared if user supplies one or more joysticks on command line: */
int autodiscover = 1;
/* -d option: */
int debug = 0;

char *joynames[MAX_STICKS + 1];
int last_joyname = 0;

const char *self;

#ifdef HAVE_X11
Display *xdisp;
int use_x = 1;
#endif

void usage(void) {
	printf("jsmond v" VERSION " by B. Watson, WTFPL\n");
	printf("Usage: %s [-c cmd] [-i interval] "
#ifdef HAVE_X11
		"[-x] "
#endif
	   "[joystick [...]]\n", self);
	printf("Build options: "
#ifndef HAVE_X11
		"no "
#endif
		"X11 support, MAX_STICKS %d, JSDEVBASE " JSDEVBASE "\n",
		MAX_STICKS);
	printf("See man page for details\n");
	exit(0);
}

void die(const char *msg) {
	fprintf(stderr, "%s: %s\n", self, msg);
	exit(1);
}

#ifdef HAVE_X11
/* make some trivial Xlib call that will result in Xlib killing
   this process if it fails. XNoOp looks like it was meant for
   exactly this, but it keeps returning 1 even if the X server is killed. */
void ping_x_server(void) {
	(void)XPending(xdisp);
	if(debug) fprintf(stderr, "X server is still alive\n");
}
#endif

void main_loop(void) {
	struct js_event e;
	int joyfds[MAX_STICKS + 1];
	int i, fdcount, active;

	fprintf(stderr, "entering main_loop()\n");

	while(1) {
		active = 0;
#ifdef HAVE_X11
		if(use_x) ping_x_server();
#endif

		/* open all the files named in the list.
		   doing it this way is more work than opening each one once before
		   main_loop() and keeping it open, but this lets us easily track
		   when devices appear and disappear. */
		fdcount = 0;
		for(i = 0; i < last_joyname; i++) {
			int synthev = 0;
			joyfds[i] = open(joynames[i], O_RDONLY | O_NONBLOCK);
			if(joyfds[i] > -1) {
				fdcount++;
				while( (read(joyfds[i], &e, sizeof(e)) > 0) && (e.type & JS_EVENT_INIT) )
					synthev++;
				if(debug)
					fprintf(stderr, "opened %s, fd %d, skipped %d synthetic events\n",
							joynames[i], joyfds[i], synthev);
			}
		}
		if(debug) fprintf(stderr, "opened %d devices, sleeping %d sec\n", fdcount, interval);

		/* let them gather events as we sleep */
		sleep(interval);

		/* now see if any of the fds got any events while we slept */
		active = 0;
		for(i = 0; i < last_joyname; i++) {
			if(joyfds[i] < 0) continue;

			if(debug) fprintf(stderr, "reading device %d, fd %d\n", i, joyfds[i]);

			/* count events. any we get here *should* be real, but it doesn't
			   hurt to mask out synthetic ones again */
			while(read(joyfds[i], &e, sizeof(e)) > 0) {
				if(!(e.type & JS_EVENT_INIT)) active++;
			}

			/* EAGAIN just means there are no more events to read.
			   anything else is a problem, though not fatal */
			if(errno != EAGAIN) {
				if(debug) fprintf(stderr, "got error on device %d: %s\n", i, strerror(errno));
			}
		}

		/* if we got any activity on any of the fds, do our thing */
		if(active) {
			int res;
			if(debug) fprintf(stderr, "*** got activity! executing: %s\n", command);
			res = system(command);
			if(debug) fprintf(stderr, "exit status %d (%s)\n", res, (res ? "failed" : "OK"));
		} else if(debug) fprintf(stderr, "no activity\n");

		/* close 'em all */
		for(i = 0; i < last_joyname; i++)
			close(joyfds[i]);
	}
}

/* make self point to our executable name without any directory */
void set_exe_name(const char *argv0) {
	const char *p;
	self = argv0;
	for(p = self; *p; p++)
		if(p[0] == '/' && p[1]) self = p + 1;
}

/* add a joystick by pathname or number. note this only gets
   called once, at startup: the list never gets modified after that. */
void add_joystick_name(const char *name) {
	if(last_joyname >= MAX_STICKS) {
		fprintf(stderr,
				"%s: too many device names, monitoring only the first %d\n",
				self,
				last_joyname);
		return;
	}

	if(*name >= '0' && *name <= '9') {
		char buf[PATH_MAX + 1];
		sprintf(buf, JSDEVBASE "%d", atoi(name));
		add_joystick_name(buf);
		return;
	}

	if( !(joynames[last_joyname] = strdup(name)) )
		die(strerror(errno));

	if(debug)
		fprintf(stderr, "added device name %d: %s\n", last_joyname, name);

	last_joyname++;
}

void enumerate_names(void) {
	int i;
	char buf[PATH_MAX + 1];

	for(i = 0; i < MAX_STICKS; i++) {
		sprintf(buf, "%s%d", JSDEVBASE, i);
		add_joystick_name(buf);
	}
}

void parse_args(int argc, char **argv) {
	if(argc > 1 && strcmp(argv[1], "--help") == 0) usage();
	while(++argv, --argc) {
		if(argv[0][0] == '-') {
			char *nextarg = argv[1];
			switch(argv[0][1]) {
#ifdef HAVE_X11
				case 'x': use_x = 0; break;
#endif
				case 'c':
					if(nextarg) {
						command = nextarg;
						argv++, argc--;
					} else {
						die("-c requires a command argument");
					}
					break;
				case 'i':
					if(nextarg && (interval = atoi(nextarg)) > 0)
						argv++, argc--;
					else
						die("-i requires a positive integer argument in seconds");
					break;
				case 'd':
					debug = 1;
					break;
				default:
					die("unrecognized argument, try --help");
					break;
			}
		} else {
			add_joystick_name(*argv);
			autodiscover = 0;
		}
	}
}

/* make ourselves a daemon, double-fork technique */
void daemonize(void) {
	pid_t pid;

	if((pid = fork()) < 0) {
		/* in parent, fork failed */
		fprintf(stderr, "%s: %s\n", self, strerror(errno));
		die("failed to daemonize");
	} else if(pid) {
		/* in parent, fork succeeded */
		exit(0);
	}

	/* the only reason for the first fork() was because setsid() can't
	   be run in the parent process */
	setsid();

	/* go on, do it again */
	if((pid = fork()) < 0) {
		/* in parent, fork failed */
		fprintf(stderr, "%s: %s\n", self, strerror(errno));
		die("failed to daemonize");
	} else if(pid) {
		/* in parent, fork succeeded */
		exit(0);
	}

	/* we no longer need stdin/out/err */
	close(0);
	close(1);
	close(2);

	/* do this so we don't keep a filesystem from being umounted because
		it's still busy (as our cwd) */
	chdir("/");
}

#ifdef HAVE_X11
void connect_to_x(void) {
	if(debug) fprintf(stderr, "connecting to X display...\n");
	xdisp = XOpenDisplay(getenv("DISPLAY"));
	if(!xdisp) die("can't connect to X server");
	if(debug) fprintf(stderr, "connected to X display\n");
}
#endif

int main(int argc, char **argv) {
	set_exe_name(argv[0]);

	parse_args(argc, argv);

	if(autodiscover) enumerate_names();

#ifdef HAVE_X11
	if(use_x) connect_to_x();
#endif

	if(!debug) daemonize();

	main_loop();

	return 0;
}