/*@internal*/
namespace ts.server {
    interface LogOptions {
        file?: string;
        detailLevel?: LogLevel;
        traceToConsole?: boolean;
        logToFile?: boolean;
    }

    interface NodeChildProcess {
        send(message: any, sendHandle?: any): void;
        on(message: "message" | "exit", f: (m: any) => void): void;
        kill(): void;
        pid: number;
    }

    interface ReadLineOptions {
        input: NodeJS.ReadableStream;
        output?: NodeJS.WritableStream;
        terminal?: boolean;
        historySize?: number;
    }

    interface NodeSocket {
        write(data: string, encoding: string): boolean;
    }

    function parseLoggingEnvironmentString(logEnvStr: string | undefined): LogOptions {
        if (!logEnvStr) {
            return {};
        }
        const logEnv: LogOptions = { logToFile: true };
        const args = logEnvStr.split(" ");
        const len = args.length - 1;
        for (let i = 0; i < len; i += 2) {
            const option = args[i];
            const { value, extraPartCounter } = getEntireValue(i + 1);
            i += extraPartCounter;
            if (option && value) {
                switch (option) {
                    case "-file":
                        logEnv.file = value;
                        break;
                    case "-level":
                        const level = getLogLevel(value);
                        logEnv.detailLevel = level !== undefined ? level : LogLevel.normal;
                        break;
                    case "-traceToConsole":
                        logEnv.traceToConsole = value.toLowerCase() === "true";
                        break;
                    case "-logToFile":
                        logEnv.logToFile = value.toLowerCase() === "true";
                        break;
                }
            }
        }
        return logEnv;

        function getEntireValue(initialIndex: number) {
            let pathStart = args[initialIndex];
            let extraPartCounter = 0;
            if (pathStart.charCodeAt(0) === CharacterCodes.doubleQuote &&
                pathStart.charCodeAt(pathStart.length - 1) !== CharacterCodes.doubleQuote) {
                for (let i = initialIndex + 1; i < args.length; i++) {
                    pathStart += " ";
                    pathStart += args[i];
                    extraPartCounter++;
                    if (pathStart.charCodeAt(pathStart.length - 1) === CharacterCodes.doubleQuote) break;
                }
            }
            return { value: stripQuotes(pathStart), extraPartCounter };
        }
    }

    function parseServerMode(): LanguageServiceMode | string | undefined {
        const mode = findArgument("--serverMode");
        if (!mode) return undefined;

        switch (mode.toLowerCase()) {
            case "semantic":
                return LanguageServiceMode.Semantic;
            case "partialsemantic":
                return LanguageServiceMode.PartialSemantic;
            case "syntactic":
                return LanguageServiceMode.Syntactic;
            default:
                return mode;
        }
    }

    export function initializeNodeSystem(): StartInput {
        const sys = Debug.checkDefined(ts.sys) as ServerHost;
        const childProcess: {
            execFileSync(file: string, args: string[], options: { stdio: "ignore", env: MapLike<string> }): string | Buffer;
        } = require("child_process");

        interface Stats {
            isFile(): boolean;
            isDirectory(): boolean;
            isBlockDevice(): boolean;
            isCharacterDevice(): boolean;
            isSymbolicLink(): boolean;
            isFIFO(): boolean;
            isSocket(): boolean;
            dev: number;
            ino: number;
            mode: number;
            nlink: number;
            uid: number;
            gid: number;
            rdev: number;
            size: number;
            blksize: number;
            blocks: number;
            atime: Date;
            mtime: Date;
            ctime: Date;
            birthtime: Date;
        }

        const fs: {
            openSync(path: string, options: string): number;
            close(fd: number, callback: (err: NodeJS.ErrnoException) => void): void;
            writeSync(fd: number, buffer: Buffer, offset: number, length: number, position?: number): number;
            statSync(path: string): Stats;
            stat(path: string, callback?: (err: NodeJS.ErrnoException, stats: Stats) => any): void;
        } = require("fs");

        class Logger extends BaseLogger {
            private fd = -1;
            constructor(
                private readonly logFilename: string,
                private readonly traceToConsole: boolean,
                level: LogLevel
            ) {
                super(level);
                if (this.logFilename) {
                    try {
                        this.fd = fs.openSync(this.logFilename, "w");
                    }
                    catch (_) {
                        // swallow the error and keep logging disabled if file cannot be opened
                    }
                }
            }

            close() {
                if (this.fd >= 0) {
                    fs.close(this.fd, noop);
                }
            }

            getLogFileName() {
                return this.logFilename;
            }

            loggingEnabled() {
                return !!this.logFilename || this.traceToConsole;
            }

            protected canWrite() {
                return this.fd >= 0 || this.traceToConsole;
            }

            protected write(s: string, _type: Msg) {
                if (this.fd >= 0) {
                    const buf = sys.bufferFrom!(s);
                    // eslint-disable-next-line no-null/no-null
                    fs.writeSync(this.fd, buf as globalThis.Buffer, 0, buf.length, /*position*/ null!); // TODO: GH#18217
                }
                if (this.traceToConsole) {
                    console.warn(s);
                }
            }
        }

        const nodeVersion = getNodeMajorVersion();
        // use watchGuard process on Windows when node version is 4 or later
        const useWatchGuard = process.platform === "win32" && nodeVersion! >= 4;
        const originalWatchDirectory: ServerHost["watchDirectory"] = sys.watchDirectory.bind(sys);
        const logger = createLogger();

        // enable deprecation logging
        Debug.loggingHost = {
            log(level, s) {
                switch (level) {
                    case ts.LogLevel.Error:
                    case ts.LogLevel.Warning:
                        return logger.msg(s, Msg.Err);
                    case ts.LogLevel.Info:
                    case ts.LogLevel.Verbose:
                        return logger.msg(s, Msg.Info);
                }
            }
        };

        const pending = createQueue<Buffer>();
        let canWrite = true;

        if (useWatchGuard) {
            const currentDrive = extractWatchDirectoryCacheKey(sys.resolvePath(sys.getCurrentDirectory()), /*currentDriveKey*/ undefined);
            const statusCache = new Map<string, boolean>();
            sys.watchDirectory = (path, callback, recursive, options) => {
                const cacheKey = extractWatchDirectoryCacheKey(path, currentDrive);
                let status = cacheKey && statusCache.get(cacheKey);
                if (status === undefined) {
                    if (logger.hasLevel(LogLevel.verbose)) {
                        logger.info(`${cacheKey} for path ${path} not found in cache...`);
                    }
                    try {
                        const args = [combinePaths(__dirname, "watchGuard.js"), path];
                        if (logger.hasLevel(LogLevel.verbose)) {
                            logger.info(`Starting ${process.execPath} with args:${stringifyIndented(args)}`);
                        }
                        childProcess.execFileSync(process.execPath, args, { stdio: "ignore", env: { ELECTRON_RUN_AS_NODE: "1" } });
                        status = true;
                        if (logger.hasLevel(LogLevel.verbose)) {
                            logger.info(`WatchGuard for path ${path} returned: OK`);
                        }
                    }
                    catch (e) {
                        status = false;
                        if (logger.hasLevel(LogLevel.verbose)) {
                            logger.info(`WatchGuard for path ${path} returned: ${e.message}`);
                        }
                    }
                    if (cacheKey) {
                        statusCache.set(cacheKey, status);
                    }
                }
                else if (logger.hasLevel(LogLevel.verbose)) {
                    logger.info(`watchDirectory for ${path} uses cached drive information.`);
                }
                if (status) {
                    // this drive is safe to use - call real 'watchDirectory'
                    return watchDirectorySwallowingException(path, callback, recursive, options);
                }
                else {
                    // this drive is unsafe - return no-op watcher
                    return noopFileWatcher;
                }
            };
        }
        else {
            sys.watchDirectory = watchDirectorySwallowingException;
        }

        // Override sys.write because fs.writeSync is not reliable on Node 4
        sys.write = (s: string) => writeMessage(sys.bufferFrom!(s, "utf8") as globalThis.Buffer);

        /* eslint-disable no-restricted-globals */
        sys.setTimeout = setTimeout;
        sys.clearTimeout = clearTimeout;
        sys.setImmediate = setImmediate;
        sys.clearImmediate = clearImmediate;
        /* eslint-enable no-restricted-globals */

        if (typeof global !== "undefined" && global.gc) {
            sys.gc = () => global.gc?.();
        }

        sys.require = (initialDir: string, moduleName: string): ModuleImportResult => {
            try {
                return { module: require(resolveJSModule(moduleName, initialDir, sys)), error: undefined };
            }
            catch (error) {
                return { module: undefined, error };
            }
        };

        let cancellationToken: ServerCancellationToken;
        try {
            const factory = require("./cancellationToken");
            cancellationToken = factory(sys.args);
        }
        catch (e) {
            cancellationToken = nullCancellationToken;
        }

        const localeStr = findArgument("--locale");
        if (localeStr) {
            validateLocaleAndSetLanguage(localeStr, sys);
        }

        const modeOrUnknown = parseServerMode();
        let serverMode: LanguageServiceMode | undefined;
        let unknownServerMode: string | undefined;
        if (modeOrUnknown !== undefined) {
            if (typeof modeOrUnknown === "number") serverMode = modeOrUnknown;
            else unknownServerMode = modeOrUnknown;
        }
        return {
            args: process.argv,
            logger,
            cancellationToken,
            serverMode,
            unknownServerMode,
            startSession: startNodeSession
        };

        // TSS_LOG "{ level: "normal | verbose | terse", file?: string}"
        function createLogger() {
            const cmdLineLogFileName = findArgument("--logFile");
            const cmdLineVerbosity = getLogLevel(findArgument("--logVerbosity"));
            const envLogOptions = parseLoggingEnvironmentString(process.env.TSS_LOG);

            const unsubstitutedLogFileName = cmdLineLogFileName
                ? stripQuotes(cmdLineLogFileName)
                : envLogOptions.logToFile
                    ? envLogOptions.file || (__dirname + "/.log" + process.pid.toString())
                    : undefined;

            const substitutedLogFileName = unsubstitutedLogFileName
                ? unsubstitutedLogFileName.replace("PID", process.pid.toString())
                : undefined;

            const logVerbosity = cmdLineVerbosity || envLogOptions.detailLevel;
            return new Logger(substitutedLogFileName!, envLogOptions.traceToConsole!, logVerbosity!); // TODO: GH#18217
        }

        function writeMessage(buf: Buffer) {
            if (!canWrite) {
                pending.enqueue(buf);
            }
            else {
                canWrite = false;
                process.stdout.write(buf, setCanWriteFlagAndWriteMessageIfNecessary);
            }
        }

        function setCanWriteFlagAndWriteMessageIfNecessary() {
            canWrite = true;
            if (!pending.isEmpty()) {
                writeMessage(pending.dequeue());
            }
        }

        function extractWatchDirectoryCacheKey(path: string, currentDriveKey: string | undefined) {
            path = normalizeSlashes(path);
            if (isUNCPath(path)) {
                // UNC path: extract server name
                // //server/location
                //         ^ <- from 0 to this position
                const firstSlash = path.indexOf(directorySeparator, 2);
                return firstSlash !== -1 ? toFileNameLowerCase(path.substring(0, firstSlash)) : path;
            }
            const rootLength = getRootLength(path);
            if (rootLength === 0) {
                // relative path - assume file is on the current drive
                return currentDriveKey;
            }
            if (path.charCodeAt(1) === CharacterCodes.colon && path.charCodeAt(2) === CharacterCodes.slash) {
                // rooted path that starts with c:/... - extract drive letter
                return toFileNameLowerCase(path.charAt(0));
            }
            if (path.charCodeAt(0) === CharacterCodes.slash && path.charCodeAt(1) !== CharacterCodes.slash) {
                // rooted path that starts with slash - /somename - use key for current drive
                return currentDriveKey;
            }
            // do not cache any other cases
            return undefined;
        }

        function isUNCPath(s: string): boolean {
            return s.length > 2 && s.charCodeAt(0) === CharacterCodes.slash && s.charCodeAt(1) === CharacterCodes.slash;
        }

        // This is the function that catches the exceptions when watching directory, and yet lets project service continue to function
        // Eg. on linux the number of watches are limited and one could easily exhaust watches and the exception ENOSPC is thrown when creating watcher at that point
        function watchDirectorySwallowingException(path: string, callback: DirectoryWatcherCallback, recursive?: boolean, options?: WatchOptions): FileWatcher {
            try {
                return originalWatchDirectory(path, callback, recursive, options);
            }
            catch (e) {
                logger.info(`Exception when creating directory watcher: ${e.message}`);
                return noopFileWatcher;
            }
        }
    }

    function parseEventPort(eventPortStr: string | undefined) {
        const eventPort = eventPortStr === undefined ? undefined : parseInt(eventPortStr);
        return eventPort !== undefined && !isNaN(eventPort) ? eventPort : undefined;
    }

    function startNodeSession(options: StartSessionOptions, logger: Logger, cancellationToken: ServerCancellationToken) {
        const childProcess: {
            fork(modulePath: string, args: string[], options?: { execArgv: string[], env?: MapLike<string> }): NodeChildProcess;
        } = require("child_process");

        const os: {
            homedir?(): string;
            tmpdir(): string;
        } = require("os");

        const net: {
            connect(options: { port: number }, onConnect?: () => void): NodeSocket
        } = require("net");

        const readline: {
            createInterface(options: ReadLineOptions): NodeJS.EventEmitter;
        } = require("readline");

        const rl = readline.createInterface({
            input: process.stdin,
            output: process.stdout,
            terminal: false,
        });

        interface QueuedOperation {
            operationId: string;
            operation: () => void;
        }

        class NodeTypingsInstaller implements ITypingsInstaller {
            private installer!: NodeChildProcess;
            private projectService!: ProjectService;
            private activeRequestCount = 0;
            private requestQueue = createQueue<QueuedOperation>();
            private requestMap = new Map<string, QueuedOperation>(); // Maps operation ID to newest requestQueue entry with that ID
            /** We will lazily request the types registry on the first call to `isKnownTypesPackageName` and store it in `typesRegistryCache`. */
            private requestedRegistry = false;
            private typesRegistryCache: ESMap<string, MapLike<string>> | undefined;

            // This number is essentially arbitrary.  Processing more than one typings request
            // at a time makes sense, but having too many in the pipe results in a hang
            // (see https://github.com/nodejs/node/issues/7657).
            // It would be preferable to base our limit on the amount of space left in the
            // buffer, but we have yet to find a way to retrieve that value.
            private static readonly maxActiveRequestCount = 10;
            private static readonly requestDelayMillis = 100;
            private packageInstalledPromise: { resolve(value: ApplyCodeActionCommandResult): void, reject(reason: unknown): void } | undefined;

            constructor(
                private readonly telemetryEnabled: boolean,
                private readonly logger: Logger,
                private readonly host: ServerHost,
                readonly globalTypingsCacheLocation: string,
                readonly typingSafeListLocation: string,
                readonly typesMapLocation: string,
                private readonly npmLocation: string | undefined,
                private readonly validateDefaultNpmLocation: boolean,
                private event: Event) {
            }

            isKnownTypesPackageName(name: string): boolean {
                // We want to avoid looking this up in the registry as that is expensive. So first check that it's actually an NPM package.
                const validationResult = JsTyping.validatePackageName(name);
                if (validationResult !== JsTyping.NameValidationResult.Ok) {
                    return false;
                }

                if (this.requestedRegistry) {
                    return !!this.typesRegistryCache && this.typesRegistryCache.has(name);
                }

                this.requestedRegistry = true;
                this.send({ kind: "typesRegistry" });
                return false;
            }

            installPackage(options: InstallPackageOptionsWithProject): Promise<ApplyCodeActionCommandResult> {
                this.send<InstallPackageRequest>({ kind: "installPackage", ...options });
                Debug.assert(this.packageInstalledPromise === undefined);
                return new Promise<ApplyCodeActionCommandResult>((resolve, reject) => {
                    this.packageInstalledPromise = { resolve, reject };
                });
            }

            attach(projectService: ProjectService) {
                this.projectService = projectService;
                if (this.logger.hasLevel(LogLevel.requestTime)) {
                    this.logger.info("Binding...");
                }

                const args: string[] = [Arguments.GlobalCacheLocation, this.globalTypingsCacheLocation];
                if (this.telemetryEnabled) {
                    args.push(Arguments.EnableTelemetry);
                }
                if (this.logger.loggingEnabled() && this.logger.getLogFileName()) {
                    args.push(Arguments.LogFile, combinePaths(getDirectoryPath(normalizeSlashes(this.logger.getLogFileName()!)), `ti-${process.pid}.log`));
                }
                if (this.typingSafeListLocation) {
                    args.push(Arguments.TypingSafeListLocation, this.typingSafeListLocation);
                }
                if (this.typesMapLocation) {
                    args.push(Arguments.TypesMapLocation, this.typesMapLocation);
                }
                if (this.npmLocation) {
                    args.push(Arguments.NpmLocation, this.npmLocation);
                }
                if (this.validateDefaultNpmLocation) {
                    args.push(Arguments.ValidateDefaultNpmLocation);
                }

                const execArgv: string[] = [];
                for (const arg of process.execArgv) {
                    const match = /^--((?:debug|inspect)(?:-brk)?)(?:=(\d+))?$/.exec(arg);
                    if (match) {
                        // if port is specified - use port + 1
                        // otherwise pick a default port depending on if 'debug' or 'inspect' and use its value + 1
                        const currentPort = match[2] !== undefined
                            ? +match[2]
                            : match[1].charAt(0) === "d" ? 5858 : 9229;
                        execArgv.push(`--${match[1]}=${currentPort + 1}`);
                        break;
                    }
                }

                this.installer = childProcess.fork(combinePaths(__dirname, "typingsInstaller.js"), args, { execArgv });
                this.installer.on("message", m => this.handleMessage(m));

                // We have to schedule this event to the next tick
                // cause this fn will be called during
                // new IOSession => super(which is Session) => new ProjectService => NodeTypingsInstaller.attach
                // and if "event" is referencing "this" before super class is initialized, it will be a ReferenceError in ES6 class.
                this.host.setImmediate(() => this.event({ pid: this.installer.pid }, "typingsInstallerPid"));

                process.on("exit", () => {
                    this.installer.kill();
                });
            }

            onProjectClosed(p: Project): void {
                this.send({ projectName: p.getProjectName(), kind: "closeProject" });
            }

            private send<T extends TypingInstallerRequestUnion>(rq: T): void {
                this.installer.send(rq);
            }

            enqueueInstallTypingsRequest(project: Project, typeAcquisition: TypeAcquisition, unresolvedImports: SortedReadonlyArray<string>): void {
                const request = createInstallTypingsRequest(project, typeAcquisition, unresolvedImports);
                if (this.logger.hasLevel(LogLevel.verbose)) {
                    if (this.logger.hasLevel(LogLevel.verbose)) {
                        this.logger.info(`Scheduling throttled operation:${stringifyIndented(request)}`);
                    }
                }

                const operationId = project.getProjectName();
                const operation = () => {
                    if (this.logger.hasLevel(LogLevel.verbose)) {
                        this.logger.info(`Sending request:${stringifyIndented(request)}`);
                    }
                    this.send(request);
                };
                const queuedRequest: QueuedOperation = { operationId, operation };

                if (this.activeRequestCount < NodeTypingsInstaller.maxActiveRequestCount) {
                    this.scheduleRequest(queuedRequest);
                }
                else {
                    if (this.logger.hasLevel(LogLevel.verbose)) {
                        this.logger.info(`Deferring request for: ${operationId}`);
                    }
                    this.requestQueue.enqueue(queuedRequest);
                    this.requestMap.set(operationId, queuedRequest);
                }
            }

            private handleMessage(response: TypesRegistryResponse | PackageInstalledResponse | SetTypings | InvalidateCachedTypings | BeginInstallTypes | EndInstallTypes | InitializationFailedResponse) {
                if (this.logger.hasLevel(LogLevel.verbose)) {
                    this.logger.info(`Received response:${stringifyIndented(response)}`);
                }

                switch (response.kind) {
                    case EventTypesRegistry:
                        this.typesRegistryCache = new Map(getEntries(response.typesRegistry));
                        break;
                    case ActionPackageInstalled: {
                        const { success, message } = response;
                        if (success) {
                            this.packageInstalledPromise!.resolve({ successMessage: message });
                        }
                        else {
                            this.packageInstalledPromise!.reject(message);
                        }
                        this.packageInstalledPromise = undefined;

                        this.projectService.updateTypingsForProject(response);

                        // The behavior is the same as for setTypings, so send the same event.
                        this.event(response, "setTypings");
                        break;
                    }
                    case EventInitializationFailed: {
                        const body: protocol.TypesInstallerInitializationFailedEventBody = {
                            message: response.message
                        };
                        const eventName: protocol.TypesInstallerInitializationFailedEventName = "typesInstallerInitializationFailed";
                        this.event(body, eventName);
                        break;
                    }
                    case EventBeginInstallTypes: {
                        const body: protocol.BeginInstallTypesEventBody = {
                            eventId: response.eventId,
                            packages: response.packagesToInstall,
                        };
                        const eventName: protocol.BeginInstallTypesEventName = "beginInstallTypes";
                        this.event(body, eventName);
                        break;
                    }
                    case EventEndInstallTypes: {
                        if (this.telemetryEnabled) {
                            const body: protocol.TypingsInstalledTelemetryEventBody = {
                                telemetryEventName: "typingsInstalled",
                                payload: {
                                    installedPackages: response.packagesToInstall.join(","),
                                    installSuccess: response.installSuccess,
                                    typingsInstallerVersion: response.typingsInstallerVersion
                                }
                            };
                            const eventName: protocol.TelemetryEventName = "telemetry";
                            this.event(body, eventName);
                        }

                        const body: protocol.EndInstallTypesEventBody = {
                            eventId: response.eventId,
                            packages: response.packagesToInstall,
                            success: response.installSuccess,
                        };
                        const eventName: protocol.EndInstallTypesEventName = "endInstallTypes";
                        this.event(body, eventName);
                        break;
                    }
                    case ActionInvalidate: {
                        this.projectService.updateTypingsForProject(response);
                        break;
                    }
                    case ActionSet: {
                        if (this.activeRequestCount > 0) {
                            this.activeRequestCount--;
                        }
                        else {
                            Debug.fail("Received too many responses");
                        }

                        while (!this.requestQueue.isEmpty()) {
                            const queuedRequest = this.requestQueue.dequeue();
                            if (this.requestMap.get(queuedRequest.operationId) === queuedRequest) {
                                this.requestMap.delete(queuedRequest.operationId);
                                this.scheduleRequest(queuedRequest);
                                break;
                            }

                            if (this.logger.hasLevel(LogLevel.verbose)) {
                                this.logger.info(`Skipping defunct request for: ${queuedRequest.operationId}`);
                            }
                        }

                        this.projectService.updateTypingsForProject(response);

                        this.event(response, "setTypings");

                        break;
                    }
                    default:
                        assertType<never>(response);
                }
            }

            private scheduleRequest(request: QueuedOperation) {
                if (this.logger.hasLevel(LogLevel.verbose)) {
                    this.logger.info(`Scheduling request for: ${request.operationId}`);
                }
                this.activeRequestCount++;
                this.host.setTimeout(request.operation, NodeTypingsInstaller.requestDelayMillis);
            }
        }

        class IOSession extends Session {
            private eventPort: number | undefined;
            private eventSocket: NodeSocket | undefined;
            private socketEventQueue: { body: any, eventName: string }[] | undefined;
            /** No longer needed if syntax target is es6 or above. Any access to "this" before initialized will be a runtime error. */
            private constructed: boolean | undefined;

            constructor() {
                const event = (body: object, eventName: string) => {
                    this.event(body, eventName);
                };

                const host = sys as ServerHost;

                const typingsInstaller = disableAutomaticTypingAcquisition
                    ? undefined
                    : new NodeTypingsInstaller(telemetryEnabled, logger, host, getGlobalTypingsCacheLocation(), typingSafeListLocation, typesMapLocation, npmLocation, validateDefaultNpmLocation, event);

                super({
                    host,
                    cancellationToken,
                    ...options,
                    typingsInstaller: typingsInstaller || nullTypingsInstaller,
                    byteLength: Buffer.byteLength,
                    hrtime: process.hrtime,
                    logger,
                    canUseEvents: true,
                    typesMapLocation,
                });

                this.eventPort = eventPort;
                if (this.canUseEvents && this.eventPort) {
                    const s = net.connect({ port: this.eventPort }, () => {
                        this.eventSocket = s;
                        if (this.socketEventQueue) {
                            // flush queue.
                            for (const event of this.socketEventQueue) {
                                this.writeToEventSocket(event.body, event.eventName);
                            }
                            this.socketEventQueue = undefined;
                        }
                    });
                }

                this.constructed = true;
            }

            event<T extends object>(body: T, eventName: string): void {
                Debug.assert(!!this.constructed, "Should only call `IOSession.prototype.event` on an initialized IOSession");

                if (this.canUseEvents && this.eventPort) {
                    if (!this.eventSocket) {
                        if (this.logger.hasLevel(LogLevel.verbose)) {
                            this.logger.info(`eventPort: event "${eventName}" queued, but socket not yet initialized`);
                        }
                        (this.socketEventQueue || (this.socketEventQueue = [])).push({ body, eventName });
                        return;
                    }
                    else {
                        Debug.assert(this.socketEventQueue === undefined);
                        this.writeToEventSocket(body, eventName);
                    }
                }
                else {
                    super.event(body, eventName);
                }
            }

            private writeToEventSocket(body: object, eventName: string): void {
                this.eventSocket!.write(formatMessage(toEvent(eventName, body), this.logger, this.byteLength, this.host.newLine), "utf8");
            }

            exit() {
                this.logger.info("Exiting...");
                this.projectService.closeLog();
                tracing?.stopTracing();
                process.exit(0);
            }

            listen() {
                rl.on("line", (input: string) => {
                    const message = input.trim();
                    this.onMessage(message);
                });

                rl.on("close", () => {
                    this.exit();
                });
            }
        }

        class IpcIOSession extends IOSession {

            protected writeMessage(msg: protocol.Message): void {
                const verboseLogging = logger.hasLevel(LogLevel.verbose);
                if (verboseLogging) {
                    const json = JSON.stringify(msg);
                    logger.info(`${msg.type}:${indent(json)}`);
                }

                process.send!(msg);
            }

            protected parseMessage(message: any): protocol.Request {
                return message as protocol.Request;
            }

            protected toStringMessage(message: any) {
                return JSON.stringify(message, undefined, 2);
            }

            public listen() {
                process.on("message", (e: any) => {
                    this.onMessage(e);
                });

                process.on("disconnect", () => {
                    this.exit();
                });
            }
        }

        const eventPort: number | undefined = parseEventPort(findArgument("--eventPort"));
        const typingSafeListLocation = findArgument(Arguments.TypingSafeListLocation)!; // TODO: GH#18217
        const typesMapLocation = findArgument(Arguments.TypesMapLocation) || combinePaths(getDirectoryPath(sys.getExecutingFilePath()), "typesMap.json");
        const npmLocation = findArgument(Arguments.NpmLocation);
        const validateDefaultNpmLocation = hasArgument(Arguments.ValidateDefaultNpmLocation);
        const disableAutomaticTypingAcquisition = hasArgument("--disableAutomaticTypingAcquisition");
        const useNodeIpc = hasArgument("--useNodeIpc");
        const telemetryEnabled = hasArgument(Arguments.EnableTelemetry);
        const commandLineTraceDir = findArgument("--traceDirectory");
        const traceDir = commandLineTraceDir
            ? stripQuotes(commandLineTraceDir)
            : process.env.TSS_TRACE;
        if (traceDir) {
            startTracing("server", traceDir);
        }

        const ioSession = useNodeIpc ? new IpcIOSession() : new IOSession();
        process.on("uncaughtException", err => {
            ioSession.logError(err, "unknown");
        });
        // See https://github.com/Microsoft/TypeScript/issues/11348
        (process as any).noAsar = true;
        // Start listening
        ioSession.listen();

        function getGlobalTypingsCacheLocation() {
            switch (process.platform) {
                case "win32": {
                    const basePath = process.env.LOCALAPPDATA ||
                        process.env.APPDATA ||
                        (os.homedir && os.homedir()) ||
                        process.env.USERPROFILE ||
                        (process.env.HOMEDRIVE && process.env.HOMEPATH && normalizeSlashes(process.env.HOMEDRIVE + process.env.HOMEPATH)) ||
                        os.tmpdir();
                    return combinePaths(combinePaths(normalizeSlashes(basePath), "Microsoft/TypeScript"), versionMajorMinor);
                }
                case "openbsd":
                case "freebsd":
                case "netbsd":
                case "darwin":
                case "linux":
                case "android": {
                    const cacheLocation = getNonWindowsCacheLocation(process.platform === "darwin");
                    return combinePaths(combinePaths(cacheLocation, "typescript"), versionMajorMinor);
                }
                default:
                    return Debug.fail(`unsupported platform '${process.platform}'`);
            }
        }

        function getNonWindowsCacheLocation(platformIsDarwin: boolean) {
            if (process.env.XDG_CACHE_HOME) {
                return process.env.XDG_CACHE_HOME;
            }
            const usersDir = platformIsDarwin ? "Users" : "home";
            const homePath = (os.homedir && os.homedir()) ||
                process.env.HOME ||
                ((process.env.LOGNAME || process.env.USER) && `/${usersDir}/${process.env.LOGNAME || process.env.USER}`) ||
                os.tmpdir();
            const cacheFolder = platformIsDarwin
                ? "Library/Caches"
                : ".cache";
            return combinePaths(normalizeSlashes(homePath), cacheFolder);
        }
    }
}
