/**
 * @module node-opcua-server
 */
// tslint:disable:no-console
import * as async from "async";
import * as chalk from "chalk";
import { EventEmitter } from "events";
import * as net from "net";
import { Server, Socket } from "net";

import { assert } from "node-opcua-assert";
import { ICertificateManager, OPCUACertificateManager } from "node-opcua-certificate-manager";
import { Certificate, convertPEMtoDER, makeSHA1Thumbprint, PrivateKeyPEM, split_der } from "node-opcua-crypto";
import { checkDebugFlag, make_debugLog, make_errorLog } from "node-opcua-debug";
import { getFullyQualifiedDomainName, resolveFullyQualifiedDomainName } from "node-opcua-hostname";
import {
    fromURI,
    MessageSecurityMode,
    SecurityPolicy,
    ServerSecureChannelLayer,
    ServerSecureChannelParent,
    toURI,
    AsymmetricAlgorithmSecurityHeader
} from "node-opcua-secure-channel";
import { UserTokenType } from "node-opcua-service-endpoints";
import { EndpointDescription } from "node-opcua-service-endpoints";
import { ApplicationDescription } from "node-opcua-service-endpoints";
import { IChannelData } from "./i_channel_data";
import { ISocketData } from "./i_socket_data";

const debugLog = make_debugLog(__filename);
const errorLog = make_errorLog(__filename);
const doDebug = checkDebugFlag(__filename);

const default_transportProfileUri = "http://opcfoundation.org/UA-Profile/Transport/uatcp-uasc-uabinary";

function extractSocketData(socket: net.Socket, reason: string): ISocketData {
    const { bytesRead, bytesWritten, remoteAddress, remoteFamily, remotePort, localAddress, localPort } = socket;
    const data: ISocketData = {
        bytesRead,
        bytesWritten,
        localAddress,
        localPort,
        remoteAddress,
        remoteFamily,
        remotePort,
        timestamp: new Date()
    };
    return data;
}

function extractChannelData(channel: ServerSecureChannelLayer): IChannelData {
    const {
        channelId,
        clientCertificate,
        clientNonce,
        clientSecurityHeader,
        securityHeader,
        securityMode,
        securityPolicy,
        timeout,
        transactionsCount
    } = channel;

    const channelData: IChannelData = {
        channelId,
        clientCertificate,
        clientNonce,
        clientSecurityHeader,
        securityHeader,
        securityMode,
        securityPolicy,
        timeout,
        transactionsCount
    };
    return channelData;
}

function dumpChannelInfo(channels: ServerSecureChannelLayer[]): void {
    function dumpChannel(channel: ServerSecureChannelLayer): void {
        console.log("------------------------------------------------------");
        console.log("            channelId = ", channel.channelId);
        console.log("             timeout  = ", channel.timeout);
        console.log("        remoteAddress = ", channel.remoteAddress);
        console.log("        remotePort    = ", channel.remotePort);
        console.log("");
        console.log("        bytesWritten  = ", channel.bytesWritten);
        console.log("        bytesRead     = ", channel.bytesRead);

        const socket = (channel as any).transport?._socket;
        if (!socket) {
            console.log(" SOCKET IS CLOSED");
        }
    }

    for (const channel of channels) {
        dumpChannel(channel);
    }
    console.log("------------------------------------------------------");
}

const emptyCertificate = Buffer.alloc(0);
const emptyPrivateKeyPEM = "";

let OPCUAServerEndPointCounter = 0;

export interface OPCUAServerEndPointOptions {
    /**
     * the tcp port
     */
    port: number;
    /**
     * the DER certificate chain
     */
    certificateChain: Certificate;

    /**
     * privateKey
     */
    privateKey: PrivateKeyPEM;

    certificateManager: OPCUACertificateManager;

    /**
     *  the default secureToken lifetime @default=60000
     */
    defaultSecureTokenLifetime?: number;

    /**
     * the maximum number of connection allowed on the TCP server socket
     * @default 20
     */
    maxConnections?: number;

    /**
     *  the  timeout for the TCP HEL/ACK transaction (in ms)
     *  @default 30000
     */
    timeout?: number;

    serverInfo: ApplicationDescription;

    objectFactory?: any;
}

export interface EndpointDescriptionParams {
    allowAnonymous?: boolean;
    restricted?: boolean;
    allowUnsecurePassword?: boolean;
    resourcePath?: string;
    alternateHostname?: string[];
    hostname: string;
}

export interface AddStandardEndpointDescriptionsParam {
    securityModes?: MessageSecurityMode[];
    securityPolicies?: SecurityPolicy[];
    disableDiscovery?: boolean;

    allowAnonymous?: boolean;
    restricted?: boolean;
    hostname?: string;
    alternateHostname?: string[];
    allowUnsecurePassword?: boolean;
    resourcePath?: string;
}

function getUniqueName(name: string, collection: { [key: string]: number }) {
    if (collection[name]) {
        let counter = 0;
        while (collection[name + "_" + counter.toString()]) {
            counter++;
        }
        name = name + "_" + counter.toString();
        collection[name] = 1;
        return name;
    } else {
        collection[name] = 1;
        return name;
    }
}
/**
 * OPCUAServerEndPoint a Server EndPoint.
 * A sever end point is listening to one port
 * note:
 *   see OPCUA Release 1.03 part 4 page 108 7.1 ApplicationDescription
 */
export class OPCUAServerEndPoint extends EventEmitter implements ServerSecureChannelParent {
    /**
     * the tcp port
     */
    public port: number;
    public certificateManager: OPCUACertificateManager;
    public defaultSecureTokenLifetime: number;
    public maxConnections: number;
    public timeout: number;
    public bytesWrittenInOldChannels: number;
    public bytesReadInOldChannels: number;
    public transactionsCountOldChannels: number;
    public securityTokenCountOldChannels: number;
    public serverInfo: ApplicationDescription;
    public objectFactory: any;

    public _on_new_channel?: (channel: ServerSecureChannelLayer) => void;
    public _on_close_channel?: (channel: ServerSecureChannelLayer) => void;
    public _on_connectionRefused?: (socketData: any) => void;
    public _on_openSecureChannelFailure?: (socketData: any, channelData: any) => void;

    private _certificateChain: Certificate;
    private _privateKey: PrivateKeyPEM;
    private _channels: { [key: string]: ServerSecureChannelLayer };
    private _server?: Server;
    private _endpoints: EndpointDescription[];
    private _listen_callback: any;
    private _started: boolean = false;
    private _counter = OPCUAServerEndPointCounter++;
    private _policy_deduplicator: { [key: string]: number } = {};
    constructor(options: OPCUAServerEndPointOptions) {
        super();

        assert(!options.hasOwnProperty("certificate"), "expecting a certificateChain instead");
        assert(options.hasOwnProperty("certificateChain"), "expecting a certificateChain");
        assert(options.hasOwnProperty("privateKey"));

        this.certificateManager = options.certificateManager;

        options.port = options.port || 0;

        this.port = parseInt(options.port.toString(), 10);
        assert(typeof this.port === "number");

        this._certificateChain = options.certificateChain;
        this._privateKey = options.privateKey;

        this._channels = {};

        this.defaultSecureTokenLifetime = options.defaultSecureTokenLifetime || 600000;

        this.maxConnections = options.maxConnections || 20;

        this.timeout = options.timeout || 30000;

        this._server = undefined;

        this._setup_server();

        this._endpoints = [];

        this.objectFactory = options.objectFactory;

        this.bytesWrittenInOldChannels = 0;
        this.bytesReadInOldChannels = 0;
        this.transactionsCountOldChannels = 0;
        this.securityTokenCountOldChannels = 0;

        this.serverInfo = options.serverInfo;
        assert(this.serverInfo !== null && typeof this.serverInfo === "object");
    }

    public dispose() {
        this._certificateChain = emptyCertificate;
        this._privateKey = emptyPrivateKeyPEM;

        assert(Object.keys(this._channels).length === 0, "OPCUAServerEndPoint channels must have been deleted");
        this._channels = {};
        this.serverInfo = new ApplicationDescription({});

        this._endpoints = [];
        assert(this._endpoints.length === 0, "endpoints must have been deleted");
        this._endpoints = [];

        this._server = undefined;
        this._listen_callback = null;

        this.removeAllListeners();
    }

    public toString(): string {
        const privateKey1 = convertPEMtoDER(this.getPrivateKey());

        const txt =
            " end point" +
            this._counter +
            " port = " +
            this.port +
            " l = " +
            this._endpoints.length +
            " " +
            makeSHA1Thumbprint(this.getCertificateChain()).toString("hex") +
            " " +
            makeSHA1Thumbprint(privateKey1).toString("hex");
        return txt;
    }

    public getChannels(): ServerSecureChannelLayer[] {
        return Object.values(this._channels);
    }

    /**
     * Returns the X509 DER form of the server certificate
     */
    public getCertificate(): Certificate {
        return split_der(this.getCertificateChain())[0];
    }

    /**
     * Returns the X509 DER form of the server certificate
     */
    public getCertificateChain(): Certificate {
        return this._certificateChain;
    }

    /**
     * the private key
     */
    public getPrivateKey(): PrivateKeyPEM {
        return this._privateKey;
    }

    /**
     * The number of active channel on this end point.
     */
    public get currentChannelCount(): number {
        return Object.keys(this._channels).length;
    }

    /**
     * @method getEndpointDescription
     * @param securityMode
     * @param securityPolicy
     * @return endpoint_description {EndpointDescription|null}
     */
    public getEndpointDescription(
        securityMode: MessageSecurityMode,
        securityPolicy: SecurityPolicy,
        endpointUrl: string | null
    ): EndpointDescription | null {
        const endpoints = this.endpointDescriptions();
        const arr = endpoints.filter(matching_endpoint.bind(this, securityMode, securityPolicy, endpointUrl));

        if (endpointUrl && endpointUrl.length > 0 && !(arr.length === 0 || arr.length === 1)) {
            errorLog("Several matching endpoints have been found : ");
            for (const a of arr) {
                errorLog("   ", a.endpointUrl, MessageSecurityMode[securityMode], securityPolicy);
            }
        }
        return arr.length === 0 ? null : arr[0];
    }

    public addEndpointDescription(
        securityMode: MessageSecurityMode,
        securityPolicy: SecurityPolicy,
        options?: EndpointDescriptionParams
    ) {
        if (!options) {
            options = { hostname: getFullyQualifiedDomainName() };
        }

        options.allowAnonymous = options.allowAnonymous === undefined ? true : options.allowAnonymous;

        // istanbul ignore next
        if (securityMode === MessageSecurityMode.None && securityPolicy !== SecurityPolicy.None) {
            throw new Error(" invalid security ");
        }
        // istanbul ignore next
        if (securityMode !== MessageSecurityMode.None && securityPolicy === SecurityPolicy.None) {
            throw new Error(" invalid security ");
        }
        //

        const port = this.port;

        // resource Path is a string added at the end of the url such as "/UA/Server"
        const resourcePath = (options.resourcePath || "").replace(/\\/g, "/");

        assert(resourcePath.length === 0 || resourcePath.charAt(0) === "/", "resourcePath should start with /");

        const hostname = options.hostname || getFullyQualifiedDomainName();
        const endpointUrl = `opc.tcp://${hostname}:${port}${resourcePath}`;

        const endpoint_desc = this.getEndpointDescription(securityMode, securityPolicy, endpointUrl);

        // istanbul ignore next
        if (endpoint_desc) {
            throw new Error(" endpoint already exist");
        }

        // now build endpointUrl
        this._endpoints.push(
            _makeEndpointDescription({
                collection: this._policy_deduplicator,
                endpointUrl,
                hostname,
                port,

                server: this.serverInfo,
                serverCertificateChain: this.getCertificateChain(),

                securityMode,
                securityPolicy,

                allowAnonymous: options.allowAnonymous,
                allowUnsecurePassword: options.allowUnsecurePassword,
                resourcePath: options.resourcePath,

                restricted: !!options.restricted
            })
        );
    }

    public addRestrictedEndpointDescription(options: EndpointDescriptionParams) {
        options = {...options};
        options.restricted = true;
        return this.addEndpointDescription(MessageSecurityMode.None, SecurityPolicy.None, options);
    }

    public addStandardEndpointDescriptions(options?: AddStandardEndpointDescriptionsParam) {
        options = options || {};

        options.securityModes = options.securityModes || defaultSecurityModes;
        options.securityPolicies = options.securityPolicies || defaultSecurityPolicies;

        const defaultHostname = options.hostname || getFullyQualifiedDomainName();

        let hostnames: string[] = [defaultHostname];

        options.alternateHostname = options.alternateHostname || [];
        if (typeof options.alternateHostname === "string") {
            options.alternateHostname = [options.alternateHostname];
        }
        // remove duplicates if any (uniq)
        hostnames =  [...new Set(hostnames.concat(options.alternateHostname as string[]))];
 
        for (const alternateHostname of hostnames) {
            const optionsE = options as EndpointDescriptionParams;
            optionsE.hostname = alternateHostname;

            if (options.securityModes.indexOf(MessageSecurityMode.None) >= 0) {
                this.addEndpointDescription(MessageSecurityMode.None, SecurityPolicy.None, optionsE);
            } else {
                if (!options.disableDiscovery) {
                    this.addRestrictedEndpointDescription(optionsE);
                }
            }
            for (const securityMode of options.securityModes) {
                if (securityMode === MessageSecurityMode.None) {
                    continue;
                }
                for (const securityPolicy of options.securityPolicies) {
                    if (securityPolicy === SecurityPolicy.None) {
                        continue;
                    }
                    this.addEndpointDescription(securityMode, securityPolicy, optionsE);
                }
            }
        }
    }

    /**
     * returns the list of end point descriptions.
     */
    public endpointDescriptions(): EndpointDescription[] {
        return this._endpoints;
    }

    /**
     * @method listen
     * @async
     */
    public listen(callback: (err?: Error) => void) {
        assert(typeof callback === "function");
        assert(!this._started, "OPCUAServerEndPoint is already listening");

        this._listen_callback = callback;

        this._server!.on("error", (err: Error) => {
            debugLog(chalk.red.bold(" error") + " port = " + this.port, err);
            this._started = false;
            this._end_listen(err);
        });
        this._server!.on("listening", () => {
            debugLog("server is listening");
        });
        this._server!.listen(
            this.port,
            /*"::",*/ (err?: Error) => {
                // 'listening' listener
                debugLog(chalk.green.bold("LISTENING TO PORT "), this.port, "err  ", err);
                assert(!err, " cannot listen to port ");
                this._started = true;
                this._end_listen();
            }
        );
    }

    public killClientSockets(callback: (err?: Error) => void) {
        for (const channel of this.getChannels()) {
            const hacked_channel = channel as any;
            if (hacked_channel.transport && hacked_channel.transport._socket) {
                // hacked_channel.transport._socket.close();
                hacked_channel.transport._socket.destroy();
                hacked_channel.transport._socket.emit("error", new Error("EPIPE"));
            }
        }
        callback();
    }

    public suspendConnection(callback: (err?: Error) => void) {
        if (!this._started) {
            return callback(new Error("Connection already suspended !!"));
        }

        // Stops the server from accepting new connections and keeps existing connections.
        // (note from nodejs doc: This function is asynchronous, the server is finally closed
        // when all connections are ended and the server emits a 'close' event.
        // The optional callback will be called once the 'close' event occurs.
        // Unlike that event, it will be called with an Error as its only argument
        // if the server was not open when it was closed.
        this._server!.close(() => {
            this._started = false;
            debugLog("Connection has been closed !" + this.port);
        });
        this._started = false;
        callback();
    }

    public restoreConnection(callback: (err?: Error) => void) {
        this.listen(callback);
    }

    public abruptlyInterruptChannels() {
        for (const channel of Object.values(this._channels)) {
            channel.abruptlyInterrupt();
        }
    }

    /**
     * @method shutdown
     * @async
     */
    public shutdown(callback: (err?: Error) => void) {
        debugLog("OPCUAServerEndPoint#shutdown ");

        if (this._started) {
            // make sure we don't accept new connection any more ...
            this.suspendConnection(() => {
                // shutdown all opened channels ...
                const _channels = Object.values(this._channels);
                async.each(
                    _channels,
                    (channel: ServerSecureChannelLayer, callback1: (err?: Error) => void) => {
                        this.shutdown_channel(channel, callback1);
                    },
                    (err?: Error | null) => {
                        /* istanbul ignore next */
                        if (!(Object.keys(this._channels).length === 0)) {
                            errorLog(" Bad !");
                        }
                        assert(Object.keys(this._channels).length === 0, "channel must have unregistered themselves");
                        callback(err || undefined);
                    }
                );
            });
        } else {
            callback();
        }
    }

    /**
     * @method start
     * @async
     * @param callback
     */
    public start(callback: (err?: Error) => void): void {
        assert(typeof callback === "function");
        this.listen(callback);
    }

    public get bytesWritten(): number {
        const channels = Object.values(this._channels);
        return (
            this.bytesWrittenInOldChannels +
            channels.reduce((accumulated: number, channel: ServerSecureChannelLayer) => {
                return accumulated + channel.bytesWritten;
            }, 0)
        );
    }

    public get bytesRead(): number {
        const channels = Object.values(this._channels);
        return (
            this.bytesReadInOldChannels +
            channels.reduce((accumulated: number, channel: ServerSecureChannelLayer) => {
                return accumulated + channel.bytesRead;
            }, 0)
        );
    }

    public get transactionsCount(): number {
        const channels = Object.values(this._channels);
        return (
            this.transactionsCountOldChannels +
            channels.reduce((accumulated: number, channel: ServerSecureChannelLayer) => {
                return accumulated + channel.transactionsCount;
            }, 0)
        );
    }

    public get securityTokenCount(): number {
        const channels = Object.values(this._channels);
        return (
            this.securityTokenCountOldChannels +
            channels.reduce((accumulated: number, channel: ServerSecureChannelLayer) => {
                return accumulated + channel.securityTokenCount;
            }, 0)
        );
    }

    public get activeChannelCount(): number {
        return Object.keys(this._channels).length;
    }

    private _dump_statistics() {
        const self = this;

        self._server!.getConnections((err: Error | null, count: number) => {
            debugLog(chalk.cyan("CONCURRENT CONNECTION = "), count);
        });
        debugLog(chalk.cyan("MAX CONNECTIONS = "), self._server!.maxConnections);
    }

    private _setup_server() {
        assert(!this._server);
        this._server = net.createServer({ pauseOnConnect: true }, this._on_client_connection.bind(this));

        // xx console.log(" Server with max connections ", self.maxConnections);
        this._server.maxConnections = this.maxConnections + 1; // plus one extra

        this._listen_callback = null;
        this._server
            .on("connection", (socket: NodeJS.Socket) => {
                // istanbul ignore next
                if (doDebug) {
                    this._dump_statistics();
                    debugLog("server connected  with : " + (socket as any).remoteAddress + ":" + (socket as any).remotePort);
                }
            })
            .on("close", () => {
                debugLog("server closed : all connections have ended");
            })
            .on("error", (err: Error) => {
                // this could be because the port is already in use
                debugLog(chalk.red.bold("server error: "), err.message);
            });
    }

    private _on_client_connection(socket: Socket) {
        // a client is attempting a connection on the socket
        (socket as any).setNoDelay(true);

        debugLog("OPCUAServerEndPoint#_on_client_connection", this._started);
        if (!this._started) {
            debugLog(
                chalk.bgWhite.cyan(
                    "OPCUAServerEndPoint#_on_client_connection " +
                        "SERVER END POINT IS PROBABLY SHUTTING DOWN !!! - Connection is refused"
                )
            );
            socket.end();
            return;
        }

        const establish_connection = () => {
            const nbConnections = Object.keys(this._channels).length;
            debugLog(
                " nbConnections ",
                nbConnections,
                " self._server.maxConnections",
                this._server!.maxConnections,
                this.maxConnections
            );
            if (nbConnections >= this.maxConnections) {
                console.log(
                    chalk.bgWhite.cyan(
                        "OPCUAServerEndPoint#_on_client_connection " +
                            "The maximum number of connection has been reached - Connection is refused"
                    )
                );
                const reason = "maxConnections reached (" + this.maxConnections + ")";
                const socketData = extractSocketData(socket, reason);
                this.emit("connectionRefused", socketData);

                socket.end();
                (socket as any).destroy();
                return;
            }

            debugLog("OPCUAServerEndPoint._on_client_connection successful => New Channel");

            const channel = new ServerSecureChannelLayer({
                defaultSecureTokenLifetime: this.defaultSecureTokenLifetime,
                // objectFactory: this.objectFactory,
                parent: this,
                timeout: this.timeout
            });

            socket.resume();

            this._preregisterChannel(channel);

            channel.init(socket, (err?: Error) => {
                this._un_pre_registerChannel(channel);
                debugLog(chalk.yellow.bold("Channel#init done"), err);
                if (err) {
                    const reason = "openSecureChannel has Failed " + err.message;
                    const socketData = extractSocketData(socket, reason);
                    const channelData = extractChannelData(channel);
                    this.emit("openSecureChannelFailure", socketData, channelData);

                    socket.end();
                    (socket as any).destroy();
                } else {
                    debugLog("server receiving a client connection");
                    this._registerChannel(channel);
                }
            });

            channel.on("message", (message: any) => {
                // forward
                this.emit("message", message, channel, this);
            });
        };
        // Each SecureChannel exists until it is explicitly closed or until the last token has expired and the overlap
        // period has elapsed. A Server application should limit the number of SecureChannels.
        // To protect against misbehaving Clients and denial of service attacks, the Server shall close the oldest
        // SecureChannel that has no Session assigned before reaching the maximum number of supported SecureChannels.
        this._prevent_DDOS_Attack(establish_connection);
    }

    private _preregisterChannel(channel: ServerSecureChannelLayer) {
        // _preregisterChannel is used to keep track of channel for which
        // that are in early stage of the hand shaking process.
        // e.g HEL/ACK and OpenSecureChannel may not have been received yet
        // as they will need to be interrupted when OPCUAServerEndPoint is closed
        assert(this._started, "OPCUAServerEndPoint must be started");

        assert(!this._channels.hasOwnProperty(channel.hashKey), " channel already preregistered!");

        this._channels[channel.hashKey] = channel;

        (channel as any)._unpreregisterChannelEvent = () => {
            debugLog("Channel received an abort event during the preregistration phase");
            this._un_pre_registerChannel(channel);
            channel.dispose();
        };
        channel.on("abort", (channel as any)._unpreregisterChannelEvent);
    }

    private _un_pre_registerChannel(channel: ServerSecureChannelLayer) {
        if (!this._channels[channel.hashKey]) {
            debugLog("Already un preregistered ?", channel.hashKey);
            return;
        }

        delete this._channels[channel.hashKey];
        assert(typeof (channel as any)._unpreregisterChannelEvent === "function");
        channel.removeListener("abort", (channel as any)._unpreregisterChannelEvent);
        (channel as any)._unpreregisterChannelEvent = null;
    }

    /**
     * @method _registerChannel
     * @param channel
     * @private
     */
    private _registerChannel(channel: ServerSecureChannelLayer) {
        if (this._started) {
            debugLog(chalk.red("_registerChannel = "), "channel.hashKey = ", channel.hashKey);

            assert(!this._channels[channel.hashKey]);
            this._channels[channel.hashKey] = channel;

            /**
             * @event newChannel
             * @param channel
             */
            this.emit("newChannel", channel);

            channel.on("abort", () => {
                this._unregisterChannel(channel);
            });
        } else {
            debugLog("OPCUAServerEndPoint#_registerChannel called when end point is shutdown !");
            debugLog("  -> channel will be forcefully terminated");
            channel.close();
            channel.dispose();
        }
    }

    /**
     * @method _unregisterChannel
     * @param channel
     * @private
     */
    private _unregisterChannel(channel: ServerSecureChannelLayer): void {
        debugLog("_un-registerChannel channel.hashKey", channel.hashKey);
        if (!this._channels.hasOwnProperty(channel.hashKey)) {
            return;
        }

        assert(this._channels.hasOwnProperty(channel.hashKey), "channel is not registered");

        /**
         * @event closeChannel
         * @param channel
         */
        this.emit("closeChannel", channel);

        // keep trace of statistics data from old channel for our own accumulated stats.
        this.bytesWrittenInOldChannels += channel.bytesWritten;
        this.bytesReadInOldChannels += channel.bytesRead;
        this.transactionsCountOldChannels += channel.transactionsCount;
        delete this._channels[channel.hashKey];

        // istanbul ignore next
        if (doDebug) {
            this._dump_statistics();
            debugLog("un-registering channel  - Count = ", this.currentChannelCount);
        }

        /// channel.dispose();
    }

    private _end_listen(err?: Error) {
        assert(typeof this._listen_callback === "function");
        this._listen_callback(err);
        this._listen_callback = null;
    }

    /**
     *  shutdown_channel
     * @param channel
     * @param inner_callback
     */
    private shutdown_channel(channel: ServerSecureChannelLayer, inner_callback: (err?: Error) => void) {
        assert(typeof inner_callback === "function");
        channel.once("close", () => {
            // xx console.log(" ON CLOSED !!!!");
        });

        channel.close(() => {
            this._unregisterChannel(channel);
            setImmediate(inner_callback);
        });
    }

    /**
     * @private
     */
    private _prevent_DDOS_Attack(establish_connection: () => void) {
        const nbConnections = this.activeChannelCount;

        if (nbConnections >= this.maxConnections) {
            // istanbul ignore next
            console.log(chalk.bgRed.white("PREVENTING DDOS ATTACK => Closing unused channels"));

            const unused_channels: ServerSecureChannelLayer[] = this.getChannels().filter(
                (channel1: ServerSecureChannelLayer) => {
                    return !channel1.isOpened && !channel1.hasSession;
                }
            );
            if (unused_channels.length === 0) {
                // all channels are in used , we cannot get any

                // istanbul ignore next
                console.log("  - all channel are used !!!!");
                dumpChannelInfo(this.getChannels());
                setImmediate(establish_connection);
                return;
            }
            // istanbul ignore next
            if (doDebug) {
                console.log(
                    "   - Unused channels that can be clobbered",
                    unused_channels.map((channel1: ServerSecureChannelLayer) => channel1.hashKey).join(" ")
                );
            }
            const channel = unused_channels[0];

            channel.close(() => {
                // istanbul ignore next
                if (doDebug) {
                    console.log("   _ Unused channel has been closed ", channel.hashKey);
                }
                this._unregisterChannel(channel);
                establish_connection();
            });
        } else {
            setImmediate(establish_connection);
        }
    }
}

interface MakeEndpointDescriptionOptions {
    /**
     * port number s
     */
    port: number;

    /**
     * @default  default hostname (default value will be full qualified domain name)
     */
    hostname: string;
    endpointUrl: string;

    serverCertificateChain: Certificate;
    securityMode: MessageSecurityMode;
    securityPolicy: SecurityPolicy;

    securityLevel?: number;

    server: ApplicationDescription;
    /*
        {
            applicationUri: string;
            applicationName: LocalizedTextOptions;
            applicationType: ApplicationType;
            gatewayServerUri: string;
            discoveryProfileUri: string;
            discoveryUrls: string[];
        };
     */
    resourcePath?: string;
    allowAnonymous?: boolean; // default true

    // allow un-encrypted password in userNameIdentity
    allowUnsecurePassword?: boolean; // default false

    restricted: boolean;

    collection: { [key: string]: number };
}

interface EndpointDescriptionEx extends EndpointDescription {
    restricted: boolean;
}

function estimateSecurityLevel(securityMode: MessageSecurityMode, securityPolicy: SecurityPolicy): number {
    if (securityMode === MessageSecurityMode.None) {
        return 1;
    }
    let offset = 100;
    if (securityMode === MessageSecurityMode.SignAndEncrypt) {
        offset = 200;
    }
    switch (securityPolicy) {
        case SecurityPolicy.Basic128:
        case SecurityPolicy.Basic128Rsa15:
        case SecurityPolicy.Basic192:
            return 2; // deprecated => low
        case SecurityPolicy.Basic192Rsa15:
            return 3; // deprecated => low
        case SecurityPolicy.Basic256:
            return 4; // deprecated => low
        case SecurityPolicy.Basic256Rsa15:
            return 4 + offset;
        case SecurityPolicy.Basic256Sha256:
            return 6 + offset;
        case SecurityPolicy.Aes128_Sha256_RsaOaep:
            return 1;

        default:
        case SecurityPolicy.None:
            return 1;
    }
}
/**
 * @private
 */
function _makeEndpointDescription(options: MakeEndpointDescriptionOptions): EndpointDescriptionEx {
    assert(isFinite(options.port), "expecting a valid port number");
    assert(options.hasOwnProperty("serverCertificateChain"));
    assert(!options.hasOwnProperty("serverCertificate"));
    assert(!!options.securityMode); // s.MessageSecurityMode
    assert(!!options.securityPolicy);
    assert(options.server !== null && typeof options.server === "object");
    assert(!!options.hostname && typeof options.hostname === "string");
    assert(typeof options.restricted === "boolean");

    const u = (n: string) => getUniqueName(n, options.collection);
    options.securityLevel =
        options.securityLevel === undefined
            ? estimateSecurityLevel(options.securityMode, options.securityPolicy)
            : options.securityLevel;
    assert(isFinite(options.securityLevel), "expecting a valid securityLevel");

    const securityPolicyUri = toURI(options.securityPolicy);

    const userIdentityTokens = [];

    if (options.securityPolicy === SecurityPolicy.None) {
        if (options.allowUnsecurePassword) {
            userIdentityTokens.push({
                policyId: u("username_unsecure"),
                tokenType: UserTokenType.UserName,

                issuedTokenType: null,
                issuerEndpointUrl: null,
                securityPolicyUri: null
            });
        }

        userIdentityTokens.push({
            policyId: u("username_basic256"),
            tokenType: UserTokenType.UserName,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: SecurityPolicy.Basic256
        });

        userIdentityTokens.push({
            policyId: u("username_basic128Rsa15"),
            tokenType: UserTokenType.UserName,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: SecurityPolicy.Basic128Rsa15
        });

        userIdentityTokens.push({
            policyId: u("username_basic256Sha256"),
            tokenType: UserTokenType.UserName,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: SecurityPolicy.Basic256Sha256
        });

        // X509
        userIdentityTokens.push({
            policyId: u("certificate_basic256"),
            tokenType: UserTokenType.UserName,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: SecurityPolicy.Basic256
        });
        userIdentityTokens.push({
            policyId: u("certificate_basic256Sha256"),
            tokenType: UserTokenType.Certificate,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: SecurityPolicy.Basic256Sha256
        });
    } else {
        // note:
        //  when channel session security is not "None",
        //  userIdentityTokens can be left to null.
        //  in this case this mean that secure policy will be the same as connection security policy
        userIdentityTokens.push({
            policyId: u("usernamePassword"),
            tokenType: UserTokenType.UserName,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: null
        });

        userIdentityTokens.push({
            policyId: u("certificateX509"),
            tokenType: UserTokenType.Certificate,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: null
        });
    }

    if (options.allowAnonymous) {
        userIdentityTokens.push({
            policyId: u("anonymous"),
            tokenType: UserTokenType.Anonymous,

            issuedTokenType: null,
            issuerEndpointUrl: null,
            securityPolicyUri: null
        });
    }

    // return the endpoint object
    const endpoint = new EndpointDescription({
        endpointUrl: options.endpointUrl,

        server: undefined, // options.server,
        serverCertificate: options.serverCertificateChain,

        securityMode: options.securityMode,
        securityPolicyUri,
        userIdentityTokens,

        securityLevel: options.securityLevel,
        transportProfileUri: default_transportProfileUri
    }) as EndpointDescriptionEx;

    (endpoint as any).__defineGetter__("endpointUrl", () => {
        return resolveFullyQualifiedDomainName(options.endpointUrl);
    });

    endpoint.server = options.server;

    endpoint.restricted = options.restricted;

    return endpoint;
}

/**
 * return true if the end point matches security mode and policy
 * @param endpoint
 * @param securityMode
 * @param securityPolicy
 * @internal
 *
 */
function matching_endpoint(
    securityMode: MessageSecurityMode,
    securityPolicy: SecurityPolicy,
    endpointUrl: string | null,
    endpoint: EndpointDescription
): boolean {
    assert(endpoint instanceof EndpointDescription);
    const endpoint_securityPolicy = fromURI(endpoint.securityPolicyUri);
    if (endpointUrl && endpoint.endpointUrl! !== endpointUrl) {
        return false;
    }
    return endpoint.securityMode === securityMode && endpoint_securityPolicy === securityPolicy;
}

const defaultSecurityModes = [MessageSecurityMode.None, MessageSecurityMode.Sign, MessageSecurityMode.SignAndEncrypt];
const defaultSecurityPolicies = [
    SecurityPolicy.Basic128Rsa15,
    SecurityPolicy.Basic256,
    // xx UNUSED!!    SecurityPolicy.Basic256Rsa15,
    SecurityPolicy.Basic256Sha256
];