import { Server } from 'socket.io';
import { MongodbPersistence } from 'y-mongodb-provider';
import { YSocketIO } from 'y-socket.io/dist/server';
import * as Y from 'yjs';

import loggerFactory from '~/utils/logger';

import { getMongoUri } from '../util/mongoose-utils';
import { RoomPrefix, getRoomNameWithId } from '../util/socket-io-helpers';

const expressSession = require('express-session');
const passport = require('passport');

const logger = loggerFactory('growi:service:socket-io');


/**
 * Serve socket.io for server-to-client messaging
 */
class SocketIoService {

  constructor(crowi) {
    this.crowi = crowi;
    this.configManager = crowi.configManager;

    this.guestClients = new Set();
  }

  get isInitialized() {
    return (this.io != null);
  }

  // Since the Order is important, attachServer() should be async
  async attachServer(server) {
    this.io = new Server({
      transports: ['websocket'],
      serveClient: false,
    });
    this.io.attach(server);

    // create the YScoketIO instance
    this.ysocketio = new YSocketIO(this.io);
    this.ysocketio.initialize();

    // create namespace for admin
    this.adminNamespace = this.io.of('/admin');

    // setup middlewares
    // !!CAUTION!! -- ORDER IS IMPORTANT
    await this.setupSessionMiddleware();
    await this.setupLoginRequiredMiddleware();
    await this.setupAdminRequiredMiddleware();
    await this.setupCheckConnectionLimitsMiddleware();

    await this.setupStoreGuestIdEventHandler();

    await this.setupLoginedUserRoomsJoinOnConnection();
    await this.setupDefaultSocketJoinRoomsEventHandler();
    await this.setupYjsConnection();
  }

  getDefaultSocket() {
    if (this.io == null) {
      throw new Error('Http server has not attached yet.');
    }
    return this.io.sockets;
  }

  getAdminSocket() {
    if (this.io == null) {
      throw new Error('Http server has not attached yet.');
    }

    return this.adminNamespace;
  }

  /**
   * use passport session
   * @see https://socket.io/docs/v4/middlewares/#Compatibility-with-Express-middleware
   */
  setupSessionMiddleware() {
    const wrap = middleware => (socket, next) => middleware(socket.request, {}, next);

    this.io.use(wrap(expressSession(this.crowi.sessionConfig)));
    this.io.use(wrap(passport.initialize()));
    this.io.use(wrap(passport.session()));

    // express and passport session on main socket doesn't shared to child namespace socket
    // need to define the session for specific namespace
    this.getAdminSocket().use(wrap(expressSession(this.crowi.sessionConfig)));
    this.getAdminSocket().use(wrap(passport.initialize()));
    this.getAdminSocket().use(wrap(passport.session()));
  }

  /**
   * use loginRequired middleware
   */
  setupLoginRequiredMiddleware() {
    const loginRequired = require('../middlewares/login-required')(this.crowi, true, (req, res, next) => {
      next(new Error('Login is required to connect.'));
    });

    // convert Connect/Express middleware to Socket.io middleware
    this.io.use((socket, next) => {
      loginRequired(socket.request, {}, next);
    });
  }

  /**
   * use adminRequired middleware
   */
  setupAdminRequiredMiddleware() {
    const adminRequired = require('../middlewares/admin-required')(this.crowi, (req, res, next) => {
      next(new Error('Admin priviledge is required to connect.'));
    });

    // convert Connect/Express middleware to Socket.io middleware
    this.getAdminSocket().use((socket, next) => {
      adminRequired(socket.request, {}, next);
    });
  }

  /**
   * use checkConnectionLimits middleware
   */
  setupCheckConnectionLimitsMiddleware() {
    this.getAdminSocket().use(this.checkConnectionLimitsForAdmin.bind(this));
    this.getDefaultSocket().use(this.checkConnectionLimitsForGuest.bind(this));
    this.getDefaultSocket().use(this.checkConnectionLimits.bind(this));
  }

  setupStoreGuestIdEventHandler() {
    this.io.on('connection', (socket) => {
      if (socket.request.user == null) {
        this.guestClients.add(socket.id);

        socket.on('disconnect', () => {
          this.guestClients.delete(socket.id);
        });
      }
    });
  }

  setupLoginedUserRoomsJoinOnConnection() {
    this.io.on('connection', (socket) => {
      const user = socket.request.user;
      if (user == null) {
        logger.debug('Socket io: An anonymous user has connected');
        return;
      }
      socket.join(getRoomNameWithId(RoomPrefix.USER, user._id));
    });
  }

  setupDefaultSocketJoinRoomsEventHandler() {
    this.io.on('connection', (socket) => {
      // set event handlers for joining rooms
      socket.on('join:page', ({ pageId }) => {
        socket.join(getRoomNameWithId(RoomPrefix.PAGE, pageId));
      });
    });
  }

  setupYjsConnection() {
    // TODO: move to packages/editor
    // https://redmine.weseek.co.jp/issues/130773
    const mdb = new MongodbPersistence(getMongoUri(), {
      collectionName: 'yjs-writings',
      flushSize: 100,
    });

    this.io.on('connection', (socket) => {
      socket.on('sync:ydoc', async({ pageId, initialValue }) => {
        // get persistent Ydoc data from DB
        const persistedYdoc = await mdb.getYDoc(pageId);
        const persistedStateVector = Y.encodeStateVector(persistedYdoc);

        // cleanup document
        await mdb.flushDocument(pageId);

        // get current Ydoc
        const currentYdoc = this.ysocketio.documents.get(`yjs/${pageId}`);

        // TODO: add error handling
        // https://redmine.weseek.co.jp/issues/130773
        if (currentYdoc == null) {
          logger.debug('currentYdoc is undefined');
          return;
        }

        const persistedCodeMirrorText = persistedYdoc.getText('codemirror').toString();
        const currentCodeMirrorText = currentYdoc.getText('codemirror').toString();
        if (persistedCodeMirrorText === '' && currentCodeMirrorText === '') {
          currentYdoc.insert(0, initialValue);
        }

        // store the new data in db (if there is any: empty update is an array of 0s)
        const diff = Y.encodeStateAsUpdate(currentYdoc, persistedStateVector);
        if (diff.reduce((previousValue, currentValue) => previousValue + currentValue, 0) > 0) {
          mdb.storeUpdate(pageId, diff);
        }

        // send persisted data to the client
        Y.applyUpdate(currentYdoc, Y.encodeStateAsUpdate(persistedYdoc));

        // persistent data is also updated when ydoc is updated
        currentYdoc.on('update', async(update, origin, doc, tr) => {
          mdb.storeUpdate(pageId, update);
        });

        // cleanup document when ydoc is destroyed
        currentYdoc.on('destroy', async(doc) => {
          await mdb.flushDocument(pageId);
        });

        // Delete old persistent data
        persistedYdoc.destroy();
      });
    });
  }

  async checkConnectionLimitsForAdmin(socket, next) {
    const namespaceName = socket.nsp.name;

    if (namespaceName === '/admin') {
      const clients = await this.getAdminSocket().allSockets();
      const clientsCount = clients.length;

      logger.debug('Current count of clients for \'/admin\':', clientsCount);

      const limit = this.configManager.getConfig('crowi', 's2cMessagingPubsub:connectionsLimitForAdmin');
      if (limit <= clientsCount) {
        const msg = `The connection was refused because the current count of clients for '/admin' is ${clientsCount} and exceeds the limit`;
        logger.warn(msg);
        next(new Error(msg));
        return;
      }
    }

    next();
  }

  async checkConnectionLimitsForGuest(socket, next) {

    if (socket.request.user == null) {
      const clientsCount = this.guestClients.size;

      logger.debug('Current count of clients for guests:', clientsCount);

      const limit = this.configManager.getConfig('crowi', 's2cMessagingPubsub:connectionsLimitForGuest');
      if (limit <= clientsCount) {
        const msg = `The connection was refused because the current count of clients for guests is ${clientsCount} and exceeds the limit`;
        logger.warn(msg);
        next(new Error(msg));
        return;
      }
    }

    next();
  }

  /**
   * @see https://socket.io/docs/server-api/#socket-client
   */
  async checkConnectionLimits(socket, next) {
    // exclude admin
    const namespaceName = socket.nsp.name;
    if (namespaceName === '/admin') {
      next();
    }

    const clients = await this.getDefaultSocket().allSockets();
    const clientsCount = clients.length;

    logger.debug('Current count of clients for \'/\':', clientsCount);

    const limit = this.configManager.getConfig('crowi', 's2cMessagingPubsub:connectionsLimit');
    if (limit <= clientsCount) {
      const msg = `The connection was refused because the current count of clients for '/' is ${clientsCount} and exceeds the limit`;
      logger.warn(msg);
      next(new Error(msg));
      return;
    }

    next();
  }

}

module.exports = SocketIoService;