/**
 * Copyright (c) Microsoft Corporation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { WebSocketServer as wsServer } from 'ws';
import { computeAllowedHosts, hostnameFromHostHeader, urlHostFromAddress } from './httpServer';
import { createHttpServer } from './network';
import { debugLogger } from './debugLogger';

import type { WebSocket, WebSocketServer } from 'ws';
import type http from 'http';
import type stream from 'stream';


let lastConnectionId = 0;
const kConnectionSymbol = Symbol('kConnection');

export const perMessageDeflate = {
  serverNoContextTakeover: true,
  zlibDeflateOptions: {
    level: 3,
  },
  zlibInflateOptions: {
    chunkSize: 10 * 1024
  },
  threshold: 10 * 1024,
};

export type WSConnection = {
  close: () => Promise<void>;
};

export type WSServerDelegate = {
  onRequest: (request: http.IncomingMessage, response: http.ServerResponse) => void;
  onHeaders: (headers: string[]) => void;
  onUpgrade: (request: http.IncomingMessage, socket: stream.Duplex) => { error: string } | undefined;
  onConnection: (request: http.IncomingMessage, url: URL, ws: WebSocket, id: string) => WSConnection;
};

export class WSServer {
  private _wsServer: WebSocketServer | undefined;
  server: http.Server | undefined;
  private _delegate: WSServerDelegate;
  // Allowed Host headers for HTTP requests. null disables the check (server bound to a public address).
  private _allowedHosts: Set<string> | null = null;

  constructor(delegate: WSServerDelegate) {
    this._delegate = delegate;
  }

  async listen(port: number = 0, hostname: string | undefined, path: string): Promise<string> {
    debugLogger.log('server', `Server started at ${new Date()}`);

    // Default to loopback so the WebSocket RPC is not exposed to the network unless
    // the caller explicitly opts in by passing a host (e.g. '0.0.0.0').
    hostname ??= 'localhost';

    const server = createHttpServer((request, response) => this._onRequest(request, response));
    server.on('error', error => debugLogger.log('server', String(error)));
    this.server = server;

    const wsEndpoint = await new Promise<string>((resolve, reject) => {
      server.listen(port, hostname, () => {
        const address = server.address();
        if (!address) {
          reject(new Error('Could not bind server socket'));
          return;
        }
        if (typeof address === 'string') {
          resolve(`${address}${path}`);
          return;
        }
        // Advertise the bound IP literal in the wsEndpoint so the client connects to
        // the same address family the server bound to. Otherwise the client and
        // server resolvers can disagree on what 'localhost' means (see #40605).
        this._allowedHosts = computeAllowedHosts(hostname, address.address);
        resolve(`ws://${urlHostFromAddress(address)}:${address.port}${path}`);
      }).on('error', reject);
    });

    debugLogger.log('server', 'Listening at ' + wsEndpoint);

    this._wsServer = new wsServer({
      noServer: true,
      perMessageDeflate,
    });

    this._wsServer.on('headers', headers => this._delegate.onHeaders(headers));

    server.on('upgrade', (request, socket, head) => {
      const pathname = new URL('http://localhost' + request.url!).pathname;
      if (pathname !== path) {
        socket.write(`HTTP/${request.httpVersion} 400 Bad Request\r\n\r\n`);
        socket.destroy();
        return;
      }
      if (this._allowedHosts && !this._isAllowedOrigin(request.headers.origin)) {
        socket.write(`HTTP/${request.httpVersion} 403 Forbidden\r\n\r\n`);
        socket.destroy();
        return;
      }
      const upgradeResult = this._delegate.onUpgrade(request, socket);
      if (upgradeResult) {
        socket.write(upgradeResult.error);
        socket.destroy();
        return;
      }
      this._wsServer!.handleUpgrade(request, socket, head, ws => this._wsServer!.emit('connection', ws, request));
    });

    this._wsServer.on('connection', (ws, request) => {
      debugLogger.log('server', 'Connected client ws.extension=' + ws.extensions);
      const url = new URL('http://localhost' + (request.url || ''));
      const id = String(++lastConnectionId);
      debugLogger.log('server', `[${id}] serving connection: ${request.url}`);
      const connection = this._delegate.onConnection(request, url, ws, id);
      (ws as any)[kConnectionSymbol] = connection;
    });

    return wsEndpoint;
  }

  private _onRequest(request: http.IncomingMessage, response: http.ServerResponse) {
    if (this._allowedHosts) {
      const host = request.headers.host?.toLowerCase();
      const hostname = host ? hostnameFromHostHeader(host) : undefined;
      if (!hostname || !this._allowedHosts.has(hostname)) {
        response.statusCode = 403;
        response.end();
        return;
      }
    }
    this._delegate.onRequest(request, response);
  }

  private _isAllowedOrigin(origin: string | undefined): boolean {
    if (!origin)
      return true;
    try {
      const hostname = new URL(origin).hostname.toLowerCase();
      const bracketed = hostname.includes(':') ? `[${hostname}]` : hostname;
      return this._allowedHosts!.has(hostname) || this._allowedHosts!.has(bracketed);
    } catch {
      return false;
    }
  }

  async close() {
    const server = this._wsServer;
    if (!server)
      return;
    debugLogger.log('server', 'closing websocket server');
    const waitForClose = new Promise(f => server.close(f));
    // First disconnect all remaining clients.
    await Promise.all(Array.from(server.clients).map(async ws => {
      const connection = (ws as any)[kConnectionSymbol] as WSConnection | undefined;
      if (connection)
        await connection.close();
      try {
        ws.terminate();
      } catch (e) {
      }
    }));
    await waitForClose;
    debugLogger.log('server', 'closing http server');
    if (this.server)
      await new Promise(f => this.server!.close(f));
    this._wsServer = undefined;
    this.server = undefined;
    debugLogger.log('server', 'closed server');
  }
}