//
// wdmtg.c: activity tracker
//
// Copyright (c) 2016 - 2020, Přemysl Eric Janouch <p@janouch.name>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//

#include <gtk/gtk.h>
#include <glib.h>
#include <sqlite3.h>

#include <stdbool.h>
#include <stdio.h>
#include <stdarg.h>
#include <locale.h>

#include <fcntl.h>
#include <sys/socket.h>
#include <sys/un.h>

#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/Xutil.h>
#include <X11/keysym.h>
#include <X11/extensions/sync.h>

#include "config.h"
#include "gui.h"

// --- Utilities ---------------------------------------------------------------

static void
exit_fatal(const gchar *format, ...) G_GNUC_PRINTF(1, 2);

static void
exit_fatal(const gchar *format, ...)
{
	va_list ap;
	va_start(ap, format);

	gchar *format_nl = g_strdup_printf("%s\n", format);
	vfprintf(stderr, format_nl, ap);
	free(format_nl);

	va_end(ap);
	exit(EXIT_FAILURE);
}

static GStrv
get_xdg_config_dirs(void)
{
	GPtrArray *paths = g_ptr_array_new();
	g_ptr_array_add(paths, g_strdup(g_get_user_config_dir()));
	for (const gchar *const *sys = g_get_system_config_dirs(); *sys; sys++)
		g_ptr_array_add(paths, g_strdup(*sys));
	g_ptr_array_add(paths, NULL);
	return (GStrv) g_ptr_array_free(paths, false);
}

// --- Globals -----------------------------------------------------------------

struct event {
	gint64 timestamp;                   // When the event happened
	gchar *title;                       // Current title at the time
	gboolean idle;                      // Whether the user is idle
};

static void
event_free(struct event *self)
{
	g_free(self->title);
	g_slice_free(struct event, self);
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

struct {
	GAsyncQueue *queue;                 // Async queue of `struct event`
} g;

struct {
	Display *dpy;                       // X display handle

	Atom net_active_window;             // _NET_ACTIVE_WINDOW
	Atom net_wm_name;                   // _NET_WM_NAME

	// Window title tracking

	gchar *current_title;               // Current window title or NULL
	Window current_window;              // Current window
	gboolean current_idle;              // Current idle status

	// XSync activity tracking

	int xsync_base_event_code;          // XSync base event code
	XSyncCounter idle_counter;          // XSync IDLETIME counter
	XSyncValue idle_timeout;            // Idle timeout

	XSyncAlarm idle_alarm_inactive;     // User is inactive
	XSyncAlarm idle_alarm_active;       // User is active
} gen;

// --- X helpers ---------------------------------------------------------------

static XSyncCounter
get_counter(const char *name)
{
	int n;
	XSyncSystemCounter *counters = XSyncListSystemCounters(gen.dpy, &n);
	XSyncCounter counter = None;
	while (n--) {
		if (!strcmp(counters[n].name, name))
			counter = counters[n].counter;
	}
	XSyncFreeSystemCounterList(counters);
	return counter;
}

static char *
x_text_property_to_utf8(XTextProperty *prop)
{
	Atom utf8_string = XInternAtom(gen.dpy, "UTF8_STRING", true);
	if (prop->encoding == utf8_string)
		return g_strdup((char *) prop->value);

	int n = 0;
	char **list = NULL;
	if (XmbTextPropertyToTextList(gen.dpy, prop, &list, &n) >= Success
		&& n > 0 && *list) {
		char *result = g_locale_to_utf8(*list, -1, NULL, NULL, NULL);
		XFreeStringList(list);
		return result;
	}
	return NULL;
}

static char *
x_text_property(Window window, Atom atom)
{
	XTextProperty name;
	XGetTextProperty(gen.dpy, window, &name, atom);
	if (!name.value)
		return NULL;

	char *result = x_text_property_to_utf8(&name);
	XFree(name.value);
	return result;
}

// --- X error handling --------------------------------------------------------

static XErrorHandler g_default_x_error_handler;

static int
on_x_error(Display *dpy, XErrorEvent *ee)
{
	// This just is going to happen since those windows aren't ours
	if (ee->error_code == BadWindow)
		return 0;
	return g_default_x_error_handler(dpy, ee);
}

// --- Application -------------------------------------------------------------

static char *
x_window_title(Window window)
{
	char *title;
	if (!(title = x_text_property(window, gen.net_wm_name))
	 && !(title = x_text_property(window, XA_WM_NAME)))
		title = g_strdup("broken");
	return title;
}

static bool
update_window_title(char *new_title)
{
	bool changed = !gen.current_title != !new_title
		|| (new_title && strcmp(gen.current_title, new_title));
	free(gen.current_title);
	gen.current_title = new_title;
	return changed;
}

static void
push_event(void) {
	struct event *event = g_slice_new0(struct event);
	event->timestamp = g_get_real_time();
	event->title = g_strdup(gen.current_title);
	event->idle = gen.current_idle;
	g_async_queue_push(g.queue, event);
}

static void
update_current_window(void)
{
	Window root = DefaultRootWindow(gen.dpy);

	Atom dummy_type; int dummy_format; unsigned long nitems, dummy_bytes;
	unsigned char *p = NULL;
	if (XGetWindowProperty(gen.dpy, root, gen.net_active_window,
		0L, 1L, false, XA_WINDOW, &dummy_type, &dummy_format,
		&nitems, &dummy_bytes, &p) != Success)
		return;

	char *new_title = NULL;
	if (nitems) {
		Window active_window = *(Window *) p;
		XFree(p);

		if (gen.current_window != active_window && gen.current_window)
			XSelectInput(gen.dpy, gen.current_window, 0);

		XSelectInput(gen.dpy, active_window, PropertyChangeMask);
		new_title = x_window_title(active_window);
		gen.current_window = active_window;
	}
	if (update_window_title(new_title)) {
		printf("Window changed: %s\n",
			gen.current_title ? gen.current_title : "(none)");
		push_event();
	}
}

static void
on_x_property_notify(XPropertyEvent *ev)
{
	// This is from the EWMH specification, set by the window manager
	if (ev->atom == gen.net_active_window) {
		update_current_window();
	} else if (ev->window == gen.current_window &&
		ev->atom == gen.net_wm_name) {
		if (update_window_title(x_window_title(ev->window))) {
			printf("Title changed: %s\n", gen.current_title);
			push_event();
		}
	}
}

static void
set_idle_alarm(XSyncAlarm *alarm, XSyncTestType test, XSyncValue value)
{
	XSyncAlarmAttributes attr;
	attr.trigger.counter = gen.idle_counter;
	attr.trigger.test_type = test;
	attr.trigger.wait_value = value;
	XSyncIntToValue(&attr.delta, 0);

	long flags = XSyncCACounter | XSyncCATestType | XSyncCAValue | XSyncCADelta;
	if (*alarm)
		XSyncChangeAlarm(gen.dpy, *alarm, flags, &attr);
	else
		*alarm = XSyncCreateAlarm(gen.dpy, flags, &attr);
}

static void
on_x_alarm_notify(XSyncAlarmNotifyEvent *ev)
{
	if (ev->alarm == gen.idle_alarm_inactive) {
		printf("User is inactive\n");
		gen.current_idle = true;
		push_event();

		XSyncValue one, minus_one;
		XSyncIntToValue(&one, 1);

		Bool overflow;
		XSyncValueSubtract(&minus_one, ev->counter_value, one, &overflow);

		// Set an alarm for IDLETIME <= current_idletime - 1
		set_idle_alarm(&gen.idle_alarm_active,
			XSyncNegativeComparison, minus_one);
	} else if (ev->alarm == gen.idle_alarm_active) {
		printf("User is active\n");
		gen.current_idle = false;
		push_event();

		set_idle_alarm(&gen.idle_alarm_inactive,
			XSyncPositiveComparison, gen.idle_timeout);
	}
}

static gboolean
on_x_ready(G_GNUC_UNUSED gpointer user_data)
{
	XEvent ev;
	while (XPending(gen.dpy)) {
		if (XNextEvent(gen.dpy, &ev))
			exit_fatal("XNextEvent returned non-zero");
		else if (ev.type == PropertyNotify)
			on_x_property_notify(&ev.xproperty);
		else if (ev.type == gen.xsync_base_event_code + XSyncAlarmNotify)
			on_x_alarm_notify((XSyncAlarmNotifyEvent *) &ev);
	}
	return G_SOURCE_CONTINUE;
}

static void
generate_events(void)
{
	GIOChannel *channel = g_io_channel_unix_new(ConnectionNumber(gen.dpy));
	GSource *watch = g_io_create_watch(channel, G_IO_IN);
	g_source_set_callback(watch, on_x_ready, NULL, NULL);

	GMainLoop *loop =
		g_main_loop_new(g_main_context_get_thread_default(), false);
	g_source_attach(watch, g_main_loop_get_context(loop));
	g_main_loop_run(loop);
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

int
main(int argc, char *argv[])
{
	gboolean show_version = false;
	const GOptionEntry options[] = {
		{"version", 'V', G_OPTION_FLAG_IN_MAIN, G_OPTION_ARG_NONE,
		 &show_version, "output version information and exit", NULL},
		{},
	};

	GError *error = NULL;
	if (!gtk_init_with_args(&argc, &argv, " - activity tracker",
		options, NULL, &error))
		exit_fatal("%s", error->message);
	if (show_version) {
		printf(PROJECT_NAME " " PROJECT_VERSION "\n");
		return 0;
	}

	g.queue = g_async_queue_new_full((GDestroyNotify) event_free);

	if (!setlocale(LC_CTYPE, ""))
		exit_fatal("cannot set locale");
	if (!XSupportsLocale())
		exit_fatal("locale not supported by Xlib");

	XInitThreads();
	if (!(gen.dpy = XOpenDisplay(NULL)))
		exit_fatal("cannot open display");

	gen.net_active_window = XInternAtom(gen.dpy, "_NET_ACTIVE_WINDOW", true);
	gen.net_wm_name       = XInternAtom(gen.dpy, "_NET_WM_NAME", true);

	// TODO: it is possible to employ a fallback mechanism via XScreenSaver
	//   by polling the XScreenSaverInfo::idle field, see
	//   https://www.x.org/releases/X11R7.5/doc/man/man3/Xss.3.html

	int dummy;
	if (!XSyncQueryExtension(gen.dpy, &gen.xsync_base_event_code, &dummy)
	 || !XSyncInitialize(gen.dpy, &dummy, &dummy))
		exit_fatal("cannot initialize XSync");

	// The idle counter is not guaranteed to exist, only SERVERTIME is
	if (!(gen.idle_counter = get_counter("IDLETIME")))
		exit_fatal("idle counter is missing");

	Window root = DefaultRootWindow(gen.dpy);
	XSelectInput(gen.dpy, root, PropertyChangeMask);
	XSync(gen.dpy, False);
	// TODO: what is the interaction with GTK+ here?
	g_default_x_error_handler = XSetErrorHandler(on_x_error);

	GKeyFile *kf = g_key_file_new();
	gchar *subpath = g_build_filename(PROJECT_NAME, PROJECT_NAME ".conf", NULL);
	GStrv dirs = get_xdg_config_dirs();

	int timeout = 600;
	if (g_key_file_load_from_dirs(kf,
		subpath, (const gchar **) dirs, NULL, 0, NULL)) {
		guint64 n = g_key_file_get_uint64(kf, "Settings", "idle_timeout", NULL);
		if (n > 0 && n <= G_MAXINT / 1000)
			timeout = n;
	}

	g_strfreev(dirs);
	g_free(subpath);
	g_key_file_free(kf);

	XSyncIntToValue(&gen.idle_timeout, timeout * 1000);
	update_current_window();
	set_idle_alarm(&gen.idle_alarm_inactive,
		XSyncPositiveComparison, gen.idle_timeout);

	gchar *data_path =
		g_build_filename(g_get_user_data_dir(), PROJECT_NAME, NULL);
	g_mkdir_with_parents(data_path, 0755);

	// TODO: try exclusivity/invocation either via DBus directly,
	// or via GApplication or GtkApplication:
	//  - GtkApplication calls Gtk.init automatically during "startup" signal,
	//    Gtk.init doesn't get command line args
	//  - "inhibiting" makes no sense, it can't be used for mere delays
	//     - actually, the "query-end" signal
	//     - should check whether it tries to exit cleanly
	//  - what is the session manager, do I have it?
	//     - "register-session" looks useful
	//     - GTK+ keeps the application running as long as it has windows,
	//       though I want to keep it running forever
	//        - g_application_hold(), perhaps
	//  - so maybe just use GApplication, that will provide more control

	// Bind to a control socket, also ensuring only one instance is running
	gchar *socket_path = g_build_filename(data_path, "socket", NULL);

	struct flock lock =
	{
		.l_type = F_WRLCK,
		.l_start = 0,
		.l_whence = SEEK_SET,
		.l_len = 0,
	};

	gchar *lock_path = g_strdup_printf("%s.lock", socket_path);
	int lock_fd = open(lock_path, O_RDWR | O_CREAT, 0644);
	if (fcntl(lock_fd, F_SETLK, &lock))
		exit_fatal("failed to acquire lock: %s", strerror(errno));
	unlink(socket_path);

	int socket_fd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (socket_fd < 0)
		exit_fatal("%s: %s", socket_path, strerror(errno));

	struct sockaddr_un sun;
	sun.sun_family = AF_UNIX;
	strncpy(sun.sun_path, socket_path, sizeof sun.sun_path);
	if (bind(socket_fd, (struct sockaddr *) &sun, sizeof sun))
		exit_fatal("%s: %s", socket_path, strerror(errno));
	if (listen(socket_fd, 10))
		exit_fatal("%s: %s", socket_path, strerror(errno));

	sqlite3 *db = NULL;
	gchar *db_path = g_build_filename(data_path, "db.sqlite", NULL);
	int rc = sqlite3_open(db_path, &db);
	if (rc != SQLITE_OK)
		exit_fatal("%s: %s", db_path, sqlite3_errmsg(db));

	// This shouldn't normally happen but external applications may decide
	// to read things out, and mess with us.  When that takes too long, we may
	// a/ wait for it to finish, b/ start with a whole-database lock or, even
	// more simply, c/ crash on the BUSY error.
	sqlite3_busy_timeout(db, 1000);

	char *errmsg = NULL;
	if ((rc = sqlite3_exec(db, "BEGIN", NULL, NULL, &errmsg)))
		exit_fatal("%s: %s", db_path, errmsg);

	sqlite3_stmt *stmt = NULL;
	if ((rc = sqlite3_prepare_v2(db, "PRAGMA user_version", -1, &stmt, NULL)))
		exit_fatal("%s: %s", db_path, sqlite3_errmsg(db));
	if ((rc = sqlite3_step(stmt)) != SQLITE_ROW ||
		sqlite3_data_count(stmt) != 1)
		exit_fatal("%s: %s", db_path, "cannot retrieve user version");

	int user_version = sqlite3_column_int(stmt, 0);
	if (user_version == 0) {
		if ((rc = sqlite3_exec(db, "CREATE TABLE events ("
			"id INTEGER PRIMARY KEY AUTOINCREMENT, "
			"timestamp INTEGER, "
			"title TEXT, "
			"idle BOOLEAN)", NULL, NULL, &errmsg)))
			exit_fatal("%s: %s", db_path, errmsg);
		if ((rc = sqlite3_exec(db, "PRAGMA user_version = 1", NULL, NULL,
			&errmsg)))
			exit_fatal("%s: %s", db_path, errmsg);
	} else if (user_version != 1) {
		exit_fatal("%s: unsupported DB version: %d", db_path, user_version);
	}
	if ((rc = sqlite3_exec(db, "COMMIT", NULL, NULL, &errmsg)))
		exit_fatal("%s: %s", db_path, errmsg);

	g_free(db_path);
	g_free(lock_path);
	g_free(socket_path);
	g_free(data_path);

	GThread *generator =
		g_thread_new("generator", (GThreadFunc) generate_events, NULL);

	// TODO: somehow read events from the async queue
	// TODO: how in the name of fuck would our custom source wake up a sleeping
	// main loop?  There is g_main_context_wakeup() but...
	//  - GWakeUp is internal, apparently

	// TODO: listen for connections on the control socket

	WdmtgWindow *window = wdmtg_window_new_with_db(db);

	gtk_main();
	g_thread_join(generator);

	free(gen.current_title);
	XCloseDisplay(gen.dpy);
	return 0;
}