//
// 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 <xcb/xcb.h>
#include <xcb/sync.h>

#include "config.h"
#include "gui.h"
#include "compound-text.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);
}

static GString *
latin1_to_utf8(const gchar *latin1, gsize len)
{
	GString *s = g_string_new(NULL);
	while (len--) {
		guchar c = *latin1++;
		if (c < 0x80) {
			g_string_append_c(s, c);
		} else {
			g_string_append_c(s, 0xC0 | (c >> 6));
			g_string_append_c(s, 0x80 | (c & 0x3F));
		}
	}
	return s;
}

// --- 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`
	sqlite3 *db;                        // Event database
} g;

struct {
	xcb_connection_t *X;                // X display handle
	xcb_screen_t *screen;               // X screen information
	GThread *thread;                    // Worker thread

	xcb_atom_t atom_net_active_window;  // _NET_ACTIVE_WINDOW
	xcb_atom_t atom_net_wm_name;        // _NET_WM_NAME
	xcb_atom_t atom_utf8_string;        // UTF8_STRING
	xcb_atom_t atom_compound_text;      // COMPOUND_TEXT

	// Window title tracking

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

	// XSync activity tracking

	const xcb_query_extension_reply_t *sync;  // Sync extension
	xcb_sync_counter_t idle_counter;          // Sync IDLETIME counter
	xcb_sync_int64_t idle_timeout;            // Idle timeout

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

// --- XCB helpers -------------------------------------------------------------

static xcb_atom_t
intern_atom(const char *atom)
{
	xcb_intern_atom_reply_t *iar = xcb_intern_atom_reply(gen.X,
		xcb_intern_atom(gen.X, false, strlen(atom), atom), NULL);
	xcb_atom_t result = iar ? iar->atom : XCB_NONE;
	free(iar);
	return result;
}

static xcb_sync_counter_t
find_counter(xcb_sync_list_system_counters_reply_t *slsr, const char *name)
{
	// FIXME: https://gitlab.freedesktop.org/xorg/lib/libxcb/-/issues/36
	const size_t xcb_sync_systemcounter_t_len = 14;

	xcb_sync_systemcounter_iterator_t slsi =
		xcb_sync_list_system_counters_counters_iterator(slsr);
	while (slsi.rem--) {
		xcb_sync_systemcounter_t *counter = slsi.data;
		char *counter_name = (char *) counter + xcb_sync_systemcounter_t_len;
		if (!strncmp(counter_name, name, counter->name_len) &&
			!name[counter->name_len])
			return counter->counter;

		slsi.data = (void *) counter +
			((xcb_sync_systemcounter_t_len + counter->name_len + 3) & ~3);
	}
	return XCB_NONE;
}

static xcb_sync_counter_t
get_counter(const char *name)
{
	xcb_sync_list_system_counters_reply_t *slsr =
		xcb_sync_list_system_counters_reply(gen.X,
			xcb_sync_list_system_counters(gen.X), NULL);

	xcb_sync_counter_t counter = XCB_NONE;
	if (slsr) {
		counter = find_counter(slsr, name);
		free(slsr);
	}
	return counter;
}

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

static GString *
x_text_property_to_utf8(GString *value, xcb_atom_t encoding)
{
	if (encoding == gen.atom_utf8_string)
		return value;

	if (encoding == XCB_ATOM_STRING) {
		// Could use g_convert() but this will certainly never fail
		GString *utf8 = latin1_to_utf8(value->str, value->len);
		g_string_free(value, true);
		return utf8;
	}

	// COMPOUND_TEXT doesn't deserve support for multiple NUL-separated items
	int *ucs4 = NULL;
	if (encoding == gen.atom_compound_text &&
		(ucs4 = compound_text_to_ucs4((char *) value->str, value->len))) {
		g_string_free(value, true);
		glong len = 0;
		gchar *utf8 = g_ucs4_to_utf8((gunichar *) ucs4, -1, NULL, &len, NULL);
		free(ucs4);

		// malloc failure or, rather theoretically, an out of range codepoint
		if (utf8) {
			value = g_string_new_len(utf8, len);
			free(utf8);
			return value;
		}
	}

	g_string_free(value, true);
	return NULL;
}

static GString *
x_text_property(xcb_window_t window, xcb_atom_t property)
{
	GString *buffer = g_string_new(NULL);
	xcb_atom_t type = XCB_NONE;
	uint32_t offset = 0;

	xcb_get_property_reply_t *gpr = NULL;
	while ((gpr = xcb_get_property_reply(gen.X,
			xcb_get_property(gen.X, false /* delete */, window,
			property, XCB_GET_PROPERTY_TYPE_ANY, offset, 0x8000), NULL))) {
		if (gpr->format != 8 || (type && gpr->type != type)) {
			free(gpr);
			break;
		}

		int len = xcb_get_property_value_length(gpr);
		g_string_append_len(buffer, xcb_get_property_value(gpr), len);
		offset += len >> 2;
		type = gpr->type;

		bool last = !gpr->bytes_after;
		free(gpr);
		if (last)
			return x_text_property_to_utf8(buffer, type);
	}
	g_string_free(buffer, true);
	return NULL;
}

// --- Async Queue Source ------------------------------------------------------

static gboolean
async_queue_source_prepare(G_GNUC_UNUSED GSource *source,
	G_GNUC_UNUSED gint *timeout_)
{
	return g_async_queue_length(g.queue) > 0;
}

static gboolean
async_queue_source_dispatch(G_GNUC_UNUSED GSource *source,
	GSourceFunc callback, gpointer user_data)
{
	// I don't want to call it once per message, prefer batch processing
	if (callback)
		return callback(user_data);

	return G_SOURCE_CONTINUE;
}

static GSource *
async_queue_source_new(void)
{
	static GSourceFuncs funcs = {
		.prepare  = async_queue_source_prepare,
		.check    = NULL,
		.dispatch = async_queue_source_dispatch,
		.finalize = NULL,
	};

	GSource *source = g_source_new(&funcs, sizeof *source);
	g_source_set_name(source, "AsyncQueueSource");
	return source;
}

// --- Generator ---------------------------------------------------------------

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);

	// This is the best thing GLib exposes (GWakeUp is internal)
	g_main_context_wakeup(g_main_context_default());
}

static char *
x_window_title(xcb_window_t window)
{
	GString *title;
	if (!(title = x_text_property(window, gen.atom_net_wm_name))
	 && !(title = x_text_property(window, XCB_ATOM_WM_NAME)))
		return g_strdup("broken");
	return g_string_free(title, false);
}

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
update_current_window(void)
{
	xcb_get_property_reply_t *gpr = xcb_get_property_reply(gen.X,
		xcb_get_property(gen.X, false /* delete */, gen.screen->root,
		gen.atom_net_active_window, XCB_ATOM_WINDOW, 0, 1), NULL);
	if (!gpr)
		return;

	// TODO: also consider watching XCB_ATOM_WM_CLASS
	//  - the first one is an "Instance name", the second one a "Class name"
	//  - don't know which one to pick, though probably the second one,
	//    since the instance name is Navigator/Mail for Firefox/Thunderbird
	//     - they are separated by a NUL character
	//  - it's not worth to watch for changes of this property

	char *new_title = NULL;
	if (xcb_get_property_value_length(gpr)) {
		xcb_window_t active_window =
			*(xcb_window_t *) xcb_get_property_value(gpr);

		const uint32_t disable[] = { 0 };
		if (gen.current_window != active_window && gen.current_window)
			(void) xcb_change_window_attributes(gen.X,
				gen.current_window, XCB_CW_EVENT_MASK, disable);

		const uint32_t enable[] = { XCB_EVENT_MASK_PROPERTY_CHANGE };
		(void) xcb_change_window_attributes(gen.X,
			active_window, XCB_CW_EVENT_MASK, enable);

		new_title = x_window_title(active_window);
		gen.current_window = active_window;
	}

	free(gpr);
	if (update_window_title(new_title))
		push_event();
}

static void
on_x_property_notify(const xcb_property_notify_event_t *ev)
{
	// This is from the EWMH specification, set by the window manager
	if (ev->atom == gen.atom_net_active_window) {
		update_current_window();
	} else if (ev->window == gen.current_window &&
		ev->atom == gen.atom_net_wm_name) {
		if (update_window_title(x_window_title(ev->window)))
			push_event();
	}
}

static void
set_idle_alarm(xcb_sync_alarm_t *alarm, xcb_sync_testtype_t test,
	xcb_sync_int64_t value)
{
	// TODO: consider xcb_sync_{change,create}_alarm_aux()
	uint32_t values[] = {
		gen.idle_counter,
		value.hi, value.lo,
		test,
		0, 0,
	};

	xcb_sync_ca_t flags = XCB_SYNC_CA_COUNTER | XCB_SYNC_CA_VALUE |
		XCB_SYNC_CA_TEST_TYPE | XCB_SYNC_CA_DELTA;
	if (*alarm) {
		xcb_sync_change_alarm(gen.X, *alarm, flags, values);
	} else {
		*alarm = xcb_generate_id(gen.X);
		xcb_sync_create_alarm(gen.X, *alarm, flags, values);
	}
}

static void
on_x_alarm_notify(const xcb_sync_alarm_notify_event_t *ev)
{
	if (ev->alarm == gen.idle_alarm_inactive) {
		gen.current_idle = true;
		push_event();

		xcb_sync_int64_t minus_one = ev->counter_value;
		if (!~(--minus_one.lo))
			minus_one.hi--;

		// Set an alarm for IDLETIME <= current_idletime - 1
		set_idle_alarm(&gen.idle_alarm_active,
			XCB_SYNC_TESTTYPE_NEGATIVE_COMPARISON, minus_one);
	} else if (ev->alarm == gen.idle_alarm_active) {
		gen.current_idle = false;
		push_event();

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

static gboolean
process_x11_event(xcb_generic_event_t *ev)
{
	int event_code = ev->response_type & 0x7f;
	if (!event_code) {
		xcb_generic_error_t *err = (xcb_generic_error_t *) ev;
		// TODO: report the error
	} else if (event_code == XCB_PROPERTY_NOTIFY) {
		on_x_property_notify((const xcb_property_notify_event_t *) ev);
	} else if (event_code == gen.sync->first_event + XCB_SYNC_ALARM_NOTIFY) {
		on_x_alarm_notify((const xcb_sync_alarm_notify_event_t *) ev);
	}
}

static gboolean
on_x_ready(G_GNUC_UNUSED gpointer user_data)
{
	xcb_generic_event_t *event;
	while ((event = xcb_poll_for_event(gen.X))) {
		process_x11_event(event);
		free(event);
	}
	(void) xcb_flush(gen.X);
	// TODO: some form of error handling, this just silently stops working
	return xcb_connection_has_error(gen.X) == 0;
}

static void
generator_thread(void)
{
	GIOChannel *channel = g_io_channel_unix_new(xcb_get_file_descriptor(gen.X));
	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);
}

static void
generator_init(void)
{
	int which_screen = -1, xcb_error;
	gen.X = xcb_connect(NULL, &which_screen);
	if ((xcb_error = xcb_connection_has_error(gen.X)))
		exit_fatal("cannot open display (code %d)", xcb_error);

	if (!(gen.atom_net_active_window = intern_atom("_NET_ACTIVE_WINDOW")) ||
		!(gen.atom_net_wm_name       = intern_atom("_NET_WM_NAME")) ||
		!(gen.atom_utf8_string       = intern_atom("UTF8_STRING")) ||
		!(gen.atom_compound_text     = intern_atom("COMPOUND_TEXT")))
		exit_fatal("unable to resolve atoms");

	// 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

	gen.sync = xcb_get_extension_data(gen.X, &xcb_sync_id);
	if (!gen.sync->present)
		exit_fatal("missing Sync extension");

	xcb_generic_error_t *err = NULL;
	xcb_sync_initialize_cookie_t sic = xcb_sync_initialize(gen.X,
		XCB_SYNC_MAJOR_VERSION, XCB_SYNC_MINOR_VERSION);
	xcb_sync_initialize_reply_t *sir =
		xcb_sync_initialize_reply(gen.X, sic, &err);
	if (!sir)
		exit_fatal("failed to initialise Sync extension");
	free(sir);

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

	const xcb_setup_t *setup = xcb_get_setup(gen.X);
	xcb_screen_iterator_t setup_iter = xcb_setup_roots_iterator(setup);
	while (which_screen--)
		xcb_screen_next(&setup_iter);

	gen.screen = setup_iter.data;
	xcb_window_t root = gen.screen->root;

	const uint32_t values[] = { XCB_EVENT_MASK_PROPERTY_CHANGE };
	(void) xcb_change_window_attributes(gen.X, root, XCB_CW_EVENT_MASK, values);
	(void) xcb_flush(gen.X);
	// TODO: how are XCB errors handled?  What if the last xcb_flush() fails?

	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);

	gint64 timeout_ms = timeout * 1000;
	gen.idle_timeout.hi = timeout_ms >> 32;
	gen.idle_timeout.lo = timeout_ms;

	update_current_window();
	set_idle_alarm(&gen.idle_alarm_inactive,
		XCB_SYNC_TESTTYPE_POSITIVE_COMPARISON, gen.idle_timeout);
}

static void
generator_launch(void)
{
	gen.thread =
		g_thread_new("generator", (GThreadFunc) generator_thread, NULL);
}

static void
generator_cleanup(void)
{
	g_thread_join(gen.thread);
	free(gen.current_title);
	xcb_disconnect(gen.X);
}

// --- Main --------------------------------------------------------------------

static gboolean
on_queue_incoming(G_GNUC_UNUSED gpointer user_data)
{
	struct event *event = NULL;
	while ((event = g_async_queue_try_pop(g.queue))) {
		printf("Event: ts: %ld, title: %s, idle: %d\n",
			event->timestamp, event->title ?: "(none)", event->idle);
		event_free(event);
	}
	return G_SOURCE_CONTINUE;
}

static sqlite3 *
database_init(const gchar *db_path)
{
	sqlite3 *db = 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 ((rc = sqlite3_finalize(stmt)))
		exit_fatal("%s: %s", db_path, "cannot retrieve user version");

	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);
	return db;
}

static int
socket_init(const gchar *socket_path)
{
	// 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

	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);
	g_free(lock_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));

	// lock_fd stays open as long as the application is running--leak
	return socket_fd;
}

int
main(int argc, char *argv[])
{
	if (!setlocale(LC_CTYPE, ""))
		exit_fatal("cannot set locale");

	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);
	generator_init();

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

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

	gchar *db_path = g_build_filename(data_path, "db.sqlite", NULL);
	g_free(data_path);
	g.db = database_init(db_path);
	g_free(db_path);

	GSource *queue_source = async_queue_source_new();
	g_source_set_callback(queue_source, on_queue_incoming, NULL, NULL);
	g_source_attach(queue_source, g_main_context_default());

	// TODO: listen for connections on the control socket

	WdmtgWindow *window = wdmtg_window_new_with_db(g.db);

	generator_launch();
	gtk_main();
	generator_cleanup();

	sqlite3_close(g.db);
	close(socket_fd);
	return 0;
}