import Gio from 'gi://Gio';
import GLib from 'gi://GLib';
import GObject from 'gi://GObject';
import St from 'gi://St';
import Clutter from 'gi://Clutter';

import * as Main from 'resource:///org/gnome/shell/ui/main.js';
import * as PanelMenu from 'resource:///org/gnome/shell/ui/panelMenu.js';
import * as PopupMenu from 'resource:///org/gnome/shell/ui/popupMenu.js';

import {Extension} from 'resource:///org/gnome/shell/extensions/extension.js';

const MIN_NORMAL_UID = 1000;
const MAX_NORMAL_UID = 60000;

const UserSwitcherIndicator = GObject.registerClass(
class UserSwitcherIndicator extends PanelMenu.Button {
	_init(extension) {
		super._init(0.0, 'User Switcher');

		this._extension = extension;
		this._ = extension.gettext.bind(extension);
		this._currentUser = GLib.get_user_name();

		const panelBox = new St.BoxLayout({
			style_class: 'panel-status-menu-box',
			y_align: Clutter.ActorAlign.CENTER,
		});

		const icon = new St.Icon({
			icon_name: 'avatar-default-symbolic',
			style_class: 'system-status-icon',
		});
		panelBox.add_child(icon);

		const label = new St.Label({
			text: this._currentUser,
			y_align: Clutter.ActorAlign.CENTER,
		});
		panelBox.add_child(label);

		this.add_child(panelBox);
		this._buildMenu();
	}

	_buildMenu() {
		this.menu.removeAll();

		const title = new PopupMenu.PopupMenuItem(
			this._('Switch User'),
			{reactive: false, can_focus: false}
		);
		title.label.add_style_class_name('popup-menu-item-title');
		this.menu.addMenuItem(title);
		this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());

		for (const user of this._getLocalUsers()) {
			const item = new PopupMenu.PopupMenuItem(user.displayName);
			if (user.username === this._currentUser)
				item.setOrnament(PopupMenu.Ornament.DOT);

			item.connect('activate', () => {
				void this._switchToUser(user.username);
			});
			this.menu.addMenuItem(item);
		}

		this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
		const loginScreenItem = new PopupMenu.PopupMenuItem(this._('Open Login Screen'));
		loginScreenItem.connect('activate', () => this._openLoginScreen());
		this.menu.addMenuItem(loginScreenItem);

		const logoutItem = new PopupMenu.PopupMenuItem(this._('Log Out'));
		logoutItem.connect('activate', () => this._logOutCurrentUser());
		this.menu.addMenuItem(logoutItem);
	}

	_getLocalUsers() {
		const users = [];
		let contents;

		try {
			[, contents] = GLib.file_get_contents('/etc/passwd');
		} catch (error) {
			log(`User Switcher: failed to read /etc/passwd: ${error}`);
			return users;
		}

		const lines = new TextDecoder().decode(contents).split('\n');
		for (const line of lines) {
			if (!line || line.startsWith('#'))
				continue;

			const fields = line.split(':');
			if (fields.length < 7)
				continue;

			const username = fields[0];
			const uid = Number.parseInt(fields[2], 10);
			const gecos = fields[4] ?? '';
			const shell = fields[6] ?? '';

			if (Number.isNaN(uid))
				continue;
			if (uid < MIN_NORMAL_UID || uid > MAX_NORMAL_UID)
				continue;
			if (shell.endsWith('/nologin') || shell.endsWith('/false'))
				continue;

			const fullName = gecos.split(',')[0].trim();
			const displayName = fullName ? `${fullName} (${username})` : username;
			users.push({username, displayName});
		}

		users.sort((a, b) => a.username.localeCompare(b.username));
		return users;
	}

	async _switchToUser(username) {
		if (username === this._currentUser)
			return;

		if (await this._activateUserSession(username))
			return;

		if (await this._runSuccessfulCommand(['dm-tool', 'switch-to-user', username]))
			return;

		Main.notify(
			this._('User Switcher'),
			this._('Direct switch is unavailable. Opening login screen instead.')
		);
		this._openLoginScreen();
	}

	_openLoginScreen() {
		const commands = [
			['gdmflexiserver'],
			['gnome-session-quit', '--switch-user', '--no-prompt'],
		];

		for (const argv of commands) {
			if (this._spawnIfAvailable(argv))
				return;
		}

		Main.notify(
			this._('User Switcher'),
			this._('No supported switch command was found on this system.')
		);
	}

	_logOutCurrentUser() {
		if (this._spawnIfAvailable(['gnome-session-quit', '--logout', '--no-prompt']))
			return;

		Main.notify(
			this._('User Switcher'),
			this._('No supported logout command was found on this system.')
		);
	}

	async _runSuccessfulCommand(argv) {
		if (!argv.length)
			return false;

		if (!GLib.find_program_in_path(argv[0]))
			return false;

		try {
			const process = Gio.Subprocess.new(
				argv,
				Gio.SubprocessFlags.STDOUT_PIPE | Gio.SubprocessFlags.STDERR_PIPE
			);
			const result = await this._communicateUtf8(process);
			return result.ok && process.get_successful();
		} catch (error) {
			log(`User Switcher: failed to start ${argv[0]}: ${error}`);
			return false;
		}
	}

	async _activateUserSession(username) {
		const sessionId = await this._getUserSessionId(username);
		if (!sessionId)
			return false;

		return this._runSuccessfulCommand(['loginctl', 'activate', sessionId]);
	}

	async _getUserSessionId(username) {
		const sessionsOutput = await this._runCommandGetStdout([
			'loginctl',
			'list-sessions',
			'--no-legend',
		]);
		if (!sessionsOutput)
			return null;

		for (const line of sessionsOutput.split('\n')) {
			const fields = line.trim().split(/\s+/);
			if (fields.length < 3)
				continue;

			const sessionId = fields[0];
			const sessionUser = fields[2];
			if (sessionUser === username)
				return sessionId;
		}

		return null;
	}

	async _runCommandGetStdout(argv) {
		if (!argv.length)
			return null;

		if (!GLib.find_program_in_path(argv[0]))
			return null;

		try {
			const process = Gio.Subprocess.new(
				argv,
				Gio.SubprocessFlags.STDOUT_PIPE | Gio.SubprocessFlags.STDERR_PIPE
			);
			const result = await this._communicateUtf8(process);
			if (!result.ok || !process.get_successful())
				return null;

			const value = result.stdout.trim();
			return value.length > 0 ? value : null;
		} catch (error) {
			log(`User Switcher: failed to run ${argv[0]}: ${error}`);
			return null;
		}
	}

	_communicateUtf8(process) {
		return new Promise(resolve => {
			process.communicate_utf8_async(null, null, (proc, res) => {
				try {
					const [ok, stdout] = proc.communicate_utf8_finish(res);
					resolve({
						ok,
						stdout: stdout ?? '',
					});
				} catch (error) {
					log(`User Switcher: command communication failed: ${error}`);
					resolve({
						ok: false,
						stdout: '',
					});
				}
			});
		});
	}

	_spawnIfAvailable(argv) {
		if (!argv.length)
			return false;

		if (!GLib.find_program_in_path(argv[0]))
			return false;

		try {
			Gio.Subprocess.new(argv, Gio.SubprocessFlags.NONE);
			return true;
		} catch (error) {
			log(`User Switcher: failed to spawn ${argv[0]}: ${error}`);
			return false;
		}
	}
});

export default class UserSwitcherExtension extends Extension {
	enable() {
		this.initTranslations();
		this._indicator = new UserSwitcherIndicator(this);
		Main.panel.addToStatusArea(this.uuid, this._indicator, 1, 'right');
	}

	disable() {
		this._indicator?.destroy();
		this._indicator = null;
	}
}