namespace ts.TestFSWithWatch {
    export const libFile: File = {
        path: "/a/lib/lib.d.ts",
        content: `/// <reference no-default-lib="true"/>
interface Boolean {}
interface Function {}
interface CallableFunction {}
interface NewableFunction {}
interface IArguments {}
interface Number { toExponential: any; }
interface Object {}
interface RegExp {}
interface String { charAt: any; }
interface Array<T> { length: number; [n: number]: T; }`
    };

    function getExecutingFilePathFromLibFile(): string {
        return combinePaths(getDirectoryPath(libFile.path), "tsc.js");
    }

    export interface TestServerHostCreationParameters {
        useCaseSensitiveFileNames?: boolean;
        executingFilePath?: string;
        currentDirectory?: string;
        newLine?: string;
        windowsStyleRoot?: string;
        environmentVariables?: ESMap<string, string>;
        runWithoutRecursiveWatches?: boolean;
        runWithFallbackPolling?: boolean;
        inodeWatching?: boolean;
    }

    export function createWatchedSystem(fileOrFolderList: FileOrFolderOrSymLinkMap | readonly FileOrFolderOrSymLink[], params?: TestServerHostCreationParameters): TestServerHost {
        return new TestServerHost(fileOrFolderList, params);
    }

    export function createServerHost(fileOrFolderList: FileOrFolderOrSymLinkMap | readonly FileOrFolderOrSymLink[], params?: TestServerHostCreationParameters): TestServerHost {
        const host = new TestServerHost(fileOrFolderList, params);
        // Just like sys, patch the host to use writeFile
        patchWriteFileEnsuringDirectory(host);
        return host;
    }

    export interface File {
        path: string;
        content: string;
        fileSize?: number;
    }

    export interface Folder {
        path: string;
    }

    export interface SymLink {
        /** Location of the symlink. */
        path: string;
        /** Relative path to the real file. */
        symLink: string;
    }

    export type FileOrFolderOrSymLink = File | Folder | SymLink;
    export interface FileOrFolderOrSymLinkMap {
        [path: string]: string | Omit<FileOrFolderOrSymLink, "path">;
    }
    export function isFile(fileOrFolderOrSymLink: FileOrFolderOrSymLink): fileOrFolderOrSymLink is File {
        return isString((fileOrFolderOrSymLink as File).content);
    }

    export function isSymLink(fileOrFolderOrSymLink: FileOrFolderOrSymLink): fileOrFolderOrSymLink is SymLink {
        return isString((fileOrFolderOrSymLink as SymLink).symLink);
    }

    interface FSEntryBase {
        path: Path;
        fullPath: string;
        modifiedTime: Date;
    }

    interface FsFile extends FSEntryBase {
        content: string;
        fileSize?: number;
    }

    interface FsFolder extends FSEntryBase {
        entries: SortedArray<FSEntry>;
    }

    interface FsSymLink extends FSEntryBase {
        symLink: string;
    }

    export type FSEntry = FsFile | FsFolder | FsSymLink;

    function isFsFolder(s: FSEntry | undefined): s is FsFolder {
        return !!s && isArray((s as FsFolder).entries);
    }

    function isFsFile(s: FSEntry | undefined): s is FsFile {
        return !!s && isString((s as FsFile).content);
    }

    function isFsSymLink(s: FSEntry | undefined): s is FsSymLink {
        return !!s && isString((s as FsSymLink).symLink);
    }

    function invokeWatcherCallbacks<T>(callbacks: readonly T[] | undefined, invokeCallback: (cb: T) => void): void {
        if (callbacks) {
            // The array copy is made to ensure that even if one of the callback removes the callbacks,
            // we dont miss any callbacks following it
            const cbs = callbacks.slice();
            for (const cb of cbs) {
                invokeCallback(cb);
            }
        }
    }

    function createWatcher<T>(map: MultiMap<Path, T>, path: Path, callback: T): FileWatcher {
        map.add(path, callback);
        let closed = false;
        return {
            close: () => {
                Debug.assert(!closed);
                map.remove(path, callback);
                closed = true;
            }
        };
    }

    export function getDiffInKeys<T>(map: ESMap<string, T>, expectedKeys: readonly string[]) {
        if (map.size === expectedKeys.length) {
            return "";
        }
        const notInActual: string[] = [];
        const duplicates: string[] = [];
        const seen = new Map<string, true>();
        forEach(expectedKeys, expectedKey => {
            if (seen.has(expectedKey)) {
                duplicates.push(expectedKey);
                return;
            }
            seen.set(expectedKey, true);
            if (!map.has(expectedKey)) {
                notInActual.push(expectedKey);
            }
        });
        const inActualNotExpected: string[] = [];
        map.forEach((_value, key) => {
            if (!seen.has(key)) {
                inActualNotExpected.push(key);
            }
            seen.set(key, true);
        });
        return `\n\nNotInActual: ${notInActual}\nDuplicates: ${duplicates}\nInActualButNotInExpected: ${inActualNotExpected}`;
    }

    export function verifyMapSize(caption: string, map: ESMap<string, any>, expectedKeys: readonly string[]) {
        assert.equal(map.size, expectedKeys.length, `${caption}: incorrect size of map: Actual keys: ${arrayFrom(map.keys())} Expected: ${expectedKeys}${getDiffInKeys(map, expectedKeys)}`);
    }

    export type MapValueTester<T, U> = [ESMap<string, U[]> | undefined, (value: T) => U];

    export function checkMap<T, U = undefined>(caption: string, actual: MultiMap<string, T>, expectedKeys: ReadonlyESMap<string, number>, valueTester?: MapValueTester<T,U>): void;
    export function checkMap<T, U = undefined>(caption: string, actual: MultiMap<string, T>, expectedKeys: readonly string[], eachKeyCount: number, valueTester?: MapValueTester<T, U>): void;
    export function checkMap<T>(caption: string, actual: ESMap<string, T> | MultiMap<string, T>, expectedKeys: readonly string[], eachKeyCount: undefined): void;
    export function checkMap<T, U = undefined>(
        caption: string,
        actual: ESMap<string, T> | MultiMap<string, T>,
        expectedKeysMapOrArray: ReadonlyESMap<string, number> | readonly string[],
        eachKeyCountOrValueTester?: number | MapValueTester<T, U>,
        valueTester?: MapValueTester<T, U>) {
        const expectedKeys = isArray(expectedKeysMapOrArray) ? arrayToMap(expectedKeysMapOrArray, s => s, () => eachKeyCountOrValueTester as number) : expectedKeysMapOrArray;
        verifyMapSize(caption, actual, isArray(expectedKeysMapOrArray) ? expectedKeysMapOrArray : arrayFrom(expectedKeys.keys()));
        if (!isNumber(eachKeyCountOrValueTester)) {
            valueTester = eachKeyCountOrValueTester;
        }
        const [expectedValues, valueMapper] = valueTester || [undefined, undefined!];
        expectedKeys.forEach((count, name) => {
            assert.isTrue(actual.has(name), `${caption}: expected to contain ${name}, actual keys: ${arrayFrom(actual.keys())}`);
            // Check key information only if eachKeyCount is provided
            if (!isArray(expectedKeysMapOrArray) || eachKeyCountOrValueTester !== undefined) {
                assert.equal((actual as MultiMap<string, T>).get(name)!.length, count, `${caption}: Expected to be have ${count} entries for ${name}. Actual entry: ${JSON.stringify(actual.get(name))}`);
                if (expectedValues) {
                    assert.deepEqual(
                        (actual as MultiMap<string, T>).get(name)!.map(valueMapper),
                        expectedValues.get(name),
                        `${caption}:: expected values mismatch for ${name}`
                    );
                }
            }
        });
    }

    export function checkArray(caption: string, actual: readonly string[], expected: readonly string[]) {
        checkMap(caption, arrayToMap(actual, identity), expected, /*eachKeyCount*/ undefined);
    }

    export function checkOutputContains(host: TestServerHost, expected: readonly string[]) {
        const mapExpected = new Set(expected);
        const mapSeen = new Set<string>();
        for (const f of host.getOutput()) {
            assert.isFalse(mapSeen.has(f), `Already found ${f} in ${JSON.stringify(host.getOutput())}`);
            if (mapExpected.has(f)) {
                mapExpected.delete(f);
                mapSeen.add(f);
            }
        }
        assert.equal(mapExpected.size, 0, `Output has missing ${JSON.stringify(arrayFrom(mapExpected.keys()))} in ${JSON.stringify(host.getOutput())}`);
    }

    export function checkOutputDoesNotContain(host: TestServerHost, expectedToBeAbsent: string[] | readonly string[]) {
        const mapExpectedToBeAbsent = new Set(expectedToBeAbsent);
        for (const f of host.getOutput()) {
            assert.isFalse(mapExpectedToBeAbsent.has(f), `Contains ${f} in ${JSON.stringify(host.getOutput())}`);
        }
    }

    interface CallbackData {
        cb: TimeOutCallback;
        args: any[];
        ms: number | undefined;
        time: number;
    }
    class Callbacks {
        private map: { cb: TimeOutCallback; args: any[]; ms: number | undefined; time: number; }[] = [];
        private nextId = 1;

        constructor(private host: TestServerHost) {
        }

        getNextId() {
            return this.nextId;
        }

        register(cb: TimeOutCallback, args: any[], ms?: number) {
            const timeoutId = this.nextId;
            this.nextId++;
            this.map[timeoutId] = { cb, args, ms, time: this.host.getTime() };
            return timeoutId;
        }

        unregister(id: any) {
            if (typeof id === "number") {
                delete this.map[id];
            }
        }

        count() {
            let n = 0;
            for (const _ in this.map) {
                n++;
            }
            return n;
        }

        private invokeCallback({ cb, args, ms, time }: CallbackData) {
            if (ms !== undefined) {
                const newTime = ms + time;
                if (this.host.getTime() < newTime) {
                    this.host.setTime(newTime);
                }
            }
            cb(...args);
        }

        invoke(invokeKey?: number) {
            if (invokeKey) {
                this.invokeCallback(this.map[invokeKey]);
                delete this.map[invokeKey];
                return;
            }

            // Note: invoking a callback may result in new callbacks been queued,
            // so do not clear the entire callback list regardless. Only remove the
            // ones we have invoked.
            for (const key in this.map) {
                this.invokeCallback(this.map[key]);
                delete this.map[key];
            }
        }
    }

    type TimeOutCallback = (...args: any[]) => void;

    export interface TestFileWatcher {
        cb: FileWatcherCallback;
        fileName: string;
        pollingInterval: PollingInterval;
    }

    export interface TestFsWatcher {
        cb: FsWatchCallback;
        directoryName: string;
        inode: number | undefined;
    }

    export interface WatchInvokeOptions {
        /** Invokes the directory watcher for the parent instead of the file changed */
        invokeDirectoryWatcherInsteadOfFileChanged: boolean;
        /** When new file is created, do not invoke watches for it */
        ignoreWatchInvokedWithTriggerAsFileCreate: boolean;
        /** Invoke the file delete, followed by create instead of file changed */
        invokeFileDeleteCreateAsPartInsteadOfChange: boolean;
        /** Dont invoke delete watches */
        ignoreDelete: boolean;
        /** Skip inode check on file or folder create*/
        skipInodeCheckOnCreate: boolean;
        /** When invoking rename event on fs watch, send event with file name suffixed with tilde */
        useTildeAsSuffixInRenameEventFileName: boolean;
    }

    export enum Tsc_WatchFile {
        DynamicPolling = "DynamicPriorityPolling",
        SingleFileWatcherPerName = "SingleFileWatcherPerName"
    }

    export enum Tsc_WatchDirectory {
        WatchFile = "RecursiveDirectoryUsingFsWatchFile",
        NonRecursiveWatchDirectory = "RecursiveDirectoryUsingNonRecursiveWatchDirectory",
        DynamicPolling = "RecursiveDirectoryUsingDynamicPriorityPolling"
    }

    export const timeIncrements = 1000;
    export interface TestServerHostOptions {
        useCaseSensitiveFileNames: boolean;
        executingFilePath: string;
        currentDirectory: string;
        newLine?: string;
        useWindowsStylePaths?: boolean;
        environmentVariables?: ESMap<string, string>;
    }

    export class TestServerHost implements server.ServerHost, FormatDiagnosticsHost, ModuleResolutionHost {
        args: string[] = [];

        private readonly output: string[] = [];

        private fs: ESMap<Path, FSEntry> = new Map();
        private time = timeIncrements;
        getCanonicalFileName: (s: string) => string;
        private toPath: (f: string) => Path;
        private timeoutCallbacks = new Callbacks(this);
        private immediateCallbacks = new Callbacks(this);
        readonly screenClears: number[] = [];

        readonly watchedFiles = createMultiMap<Path, TestFileWatcher>();
        readonly fsWatches = createMultiMap<Path, TestFsWatcher>();
        readonly fsWatchesRecursive = createMultiMap<Path, TestFsWatcher>();
        runWithFallbackPolling: boolean;
        public readonly useCaseSensitiveFileNames: boolean;
        public readonly newLine: string;
        public readonly windowsStyleRoot?: string;
        private readonly environmentVariables?: ESMap<string, string>;
        private readonly executingFilePath: string;
        private readonly currentDirectory: string;
        public require: ((initialPath: string, moduleName: string) => RequireResult) | undefined;
        public defaultWatchFileKind?: () => WatchFileKind | undefined;
        public storeFilesChangingSignatureDuringEmit = true;
        watchFile: HostWatchFile;
        private inodeWatching: boolean | undefined;
        private readonly inodes?: ESMap<Path, number>;
        watchDirectory: HostWatchDirectory;
        constructor(
            fileOrFolderorSymLinkList: FileOrFolderOrSymLinkMap | readonly FileOrFolderOrSymLink[],
            {
                useCaseSensitiveFileNames, executingFilePath, currentDirectory,
                newLine, windowsStyleRoot, environmentVariables,
                runWithoutRecursiveWatches, runWithFallbackPolling,
                inodeWatching,
            }: TestServerHostCreationParameters = {}) {
            this.useCaseSensitiveFileNames = !!useCaseSensitiveFileNames;
            this.newLine = newLine || "\n";
            this.windowsStyleRoot = windowsStyleRoot;
            this.environmentVariables = environmentVariables;
            currentDirectory = currentDirectory || "/";
            this.getCanonicalFileName = createGetCanonicalFileName(!!useCaseSensitiveFileNames);
            this.toPath = s => toPath(s, currentDirectory, this.getCanonicalFileName);
            this.executingFilePath = this.getHostSpecificPath(executingFilePath || getExecutingFilePathFromLibFile());
            this.currentDirectory = this.getHostSpecificPath(currentDirectory);
            this.runWithFallbackPolling = !!runWithFallbackPolling;
            const tscWatchFile = this.environmentVariables && this.environmentVariables.get("TSC_WATCHFILE");
            const tscWatchDirectory = this.environmentVariables && this.environmentVariables.get("TSC_WATCHDIRECTORY");
            if (inodeWatching) {
                this.inodeWatching = true;
                this.inodes = new Map();
            }

            const { watchFile, watchDirectory } = createSystemWatchFunctions({
                // We dont have polling watch file
                // it is essentially fsWatch but lets get that separate from fsWatch and
                // into watchedFiles for easier testing
                pollingWatchFile: tscWatchFile === Tsc_WatchFile.SingleFileWatcherPerName ?
                    createSingleFileWatcherPerName(
                        this.watchFileWorker.bind(this),
                        this.useCaseSensitiveFileNames
                    ) :
                    this.watchFileWorker.bind(this),
                getModifiedTime: this.getModifiedTime.bind(this),
                setTimeout: this.setTimeout.bind(this),
                clearTimeout: this.clearTimeout.bind(this),
                fsWatchWorker: this.fsWatchWorker.bind(this),
                fileSystemEntryExists: this.fileSystemEntryExists.bind(this),
                useCaseSensitiveFileNames: this.useCaseSensitiveFileNames,
                getCurrentDirectory: this.getCurrentDirectory.bind(this),
                fsSupportsRecursiveFsWatch: tscWatchDirectory ? false : !runWithoutRecursiveWatches,
                getAccessibleSortedChildDirectories: path => this.getDirectories(path),
                realpath: this.realpath.bind(this),
                tscWatchFile,
                tscWatchDirectory,
                defaultWatchFileKind: () => this.defaultWatchFileKind?.(),
                inodeWatching: !!this.inodeWatching,
                sysLog: s => this.write(s + this.newLine),
            });
            this.watchFile = watchFile;
            this.watchDirectory = watchDirectory;
            this.reloadFS(fileOrFolderorSymLinkList);
        }

        private nextInode = 0;
        private setInode(path: Path) {
            if (this.inodes) this.inodes.set(path, this.nextInode++);
        }

        // Output is pretty
        writeOutputIsTTY() {
            return true;
        }

        getNewLine() {
            return this.newLine;
        }

        toNormalizedAbsolutePath(s: string) {
            return getNormalizedAbsolutePath(s, this.currentDirectory);
        }

        toFullPath(s: string) {
            return this.toPath(this.toNormalizedAbsolutePath(s));
        }

        getHostSpecificPath(s: string) {
            if (this.windowsStyleRoot && s.startsWith(directorySeparator)) {
                return this.windowsStyleRoot + s.substring(1);
            }
            return s;
        }

        now() {
            this.time += timeIncrements;
            return new Date(this.time);
        }

        getTime() {
            return this.time;
        }

        setTime(time: number) {
            this.time = time;
        }

        private reloadFS(fileOrFolderOrSymLinkList: FileOrFolderOrSymLinkMap | readonly FileOrFolderOrSymLink[]) {
            Debug.assert(this.fs.size === 0);
            if (isArray(fileOrFolderOrSymLinkList)) {
                fileOrFolderOrSymLinkList.forEach(f => this.ensureFileOrFolder(!this.windowsStyleRoot ?
                    f :
                    { ...f, path: this.getHostSpecificPath(f.path) }
                ));
            }
            else {
                for (const key in fileOrFolderOrSymLinkList) {
                    if (hasProperty(fileOrFolderOrSymLinkList, key)) {
                        const path = this.getHostSpecificPath(key);
                        const value = fileOrFolderOrSymLinkList[key];
                        if (isString(value)) {
                            this.ensureFileOrFolder({ path, content: value });
                        }
                        else {
                            this.ensureFileOrFolder({ path, ...value });
                        }
                    }
                }
            }
        }

        modifyFile(filePath: string, content: string, options?: Partial<WatchInvokeOptions>) {
            const path = this.toFullPath(filePath);
            const currentEntry = this.fs.get(path);
            if (!currentEntry || !isFsFile(currentEntry)) {
                throw new Error(`file not present: ${filePath}`);
            }

            if (options && options.invokeFileDeleteCreateAsPartInsteadOfChange) {
                this.removeFileOrFolder(currentEntry, /*isRenaming*/ false, options);
                this.ensureFileOrFolder({ path: filePath, content }, /*ignoreWatchInvokedWithTriggerAsFileCreate*/ undefined, /*ignoreParentWatch*/ undefined, options);
            }
            else {
                currentEntry.content = content;
                currentEntry.modifiedTime = this.now();
                this.fs.get(getDirectoryPath(currentEntry.path))!.modifiedTime = this.now();
                if (options && options.invokeDirectoryWatcherInsteadOfFileChanged) {
                    const directoryFullPath = getDirectoryPath(currentEntry.fullPath);
                    this.invokeFileWatcher(directoryFullPath, FileWatcherEventKind.Changed, currentEntry.modifiedTime, /*useFileNameInCallback*/ true);
                    this.invokeFsWatchesCallbacks(directoryFullPath, "rename", currentEntry.modifiedTime, currentEntry.fullPath, options.useTildeAsSuffixInRenameEventFileName);
                    this.invokeRecursiveFsWatches(directoryFullPath, "rename", currentEntry.modifiedTime, currentEntry.fullPath, options.useTildeAsSuffixInRenameEventFileName);
                }
                else {
                    this.invokeFileAndFsWatches(currentEntry.fullPath, FileWatcherEventKind.Changed, currentEntry.modifiedTime, options?.useTildeAsSuffixInRenameEventFileName);
                }
            }
        }

        renameFile(fileName: string, newFileName: string) {
            const fullPath = getNormalizedAbsolutePath(fileName, this.currentDirectory);
            const path = this.toPath(fullPath);
            const file = this.fs.get(path) as FsFile;
            Debug.assert(!!file);

            // Only remove the file
            this.removeFileOrFolder(file, /*isRenaming*/ true);

            // Add updated folder with new folder name
            const newFullPath = getNormalizedAbsolutePath(newFileName, this.currentDirectory);
            const newFile = this.toFsFile({ path: newFullPath, content: file.content });
            const newPath = newFile.path;
            const basePath = getDirectoryPath(path);
            Debug.assert(basePath !== path);
            Debug.assert(basePath === getDirectoryPath(newPath));
            const baseFolder = this.fs.get(basePath) as FsFolder;
            this.addFileOrFolderInFolder(baseFolder, newFile);
        }

        renameFolder(folderName: string, newFolderName: string) {
            const fullPath = getNormalizedAbsolutePath(folderName, this.currentDirectory);
            const path = this.toPath(fullPath);
            const folder = this.fs.get(path) as FsFolder;
            Debug.assert(!!folder);

            // Only remove the folder
            this.removeFileOrFolder(folder, /*isRenaming*/ true);

            // Add updated folder with new folder name
            const newFullPath = getNormalizedAbsolutePath(newFolderName, this.currentDirectory);
            const newFolder = this.toFsFolder(newFullPath);
            const newPath = newFolder.path;
            const basePath = getDirectoryPath(path);
            Debug.assert(basePath !== path);
            Debug.assert(basePath === getDirectoryPath(newPath));
            const baseFolder = this.fs.get(basePath) as FsFolder;
            this.addFileOrFolderInFolder(baseFolder, newFolder);

            // Invoke watches for files in the folder as deleted (from old path)
            this.renameFolderEntries(folder, newFolder);
        }

        private renameFolderEntries(oldFolder: FsFolder, newFolder: FsFolder) {
            for (const entry of oldFolder.entries) {
                this.fs.delete(entry.path);
                this.invokeFileAndFsWatches(entry.fullPath, FileWatcherEventKind.Deleted);

                entry.fullPath = combinePaths(newFolder.fullPath, getBaseFileName(entry.fullPath));
                entry.path = this.toPath(entry.fullPath);
                if (newFolder !== oldFolder) {
                    newFolder.entries.push(entry);
                }
                this.fs.set(entry.path, entry);
                this.setInode(entry.path);
                this.invokeFileAndFsWatches(entry.fullPath, FileWatcherEventKind.Created);
                if (isFsFolder(entry)) {
                    this.renameFolderEntries(entry, entry);
                }
            }
        }

        ensureFileOrFolder(fileOrDirectoryOrSymLink: FileOrFolderOrSymLink, ignoreWatchInvokedWithTriggerAsFileCreate?: boolean, ignoreParentWatch?: boolean, options?: Partial<WatchInvokeOptions>) {
            if (isFile(fileOrDirectoryOrSymLink)) {
                const file = this.toFsFile(fileOrDirectoryOrSymLink);
                // file may already exist when updating existing type declaration file
                if (!this.fs.get(file.path)) {
                    const baseFolder = this.ensureFolder(getDirectoryPath(file.fullPath), ignoreParentWatch, options);
                    this.addFileOrFolderInFolder(baseFolder, file, ignoreWatchInvokedWithTriggerAsFileCreate, options);
                }
            }
            else if (isSymLink(fileOrDirectoryOrSymLink)) {
                const symLink = this.toFsSymLink(fileOrDirectoryOrSymLink);
                Debug.assert(!this.fs.get(symLink.path));
                const baseFolder = this.ensureFolder(getDirectoryPath(symLink.fullPath), ignoreParentWatch, options);
                this.addFileOrFolderInFolder(baseFolder, symLink, ignoreWatchInvokedWithTriggerAsFileCreate, options);
            }
            else {
                const fullPath = getNormalizedAbsolutePath(fileOrDirectoryOrSymLink.path, this.currentDirectory);
                this.ensureFolder(getDirectoryPath(fullPath), ignoreParentWatch, options);
                this.ensureFolder(fullPath, ignoreWatchInvokedWithTriggerAsFileCreate, options);
            }
        }

        private ensureFolder(fullPath: string, ignoreWatch: boolean | undefined, options: Partial<WatchInvokeOptions> | undefined): FsFolder {
            const path = this.toPath(fullPath);
            let folder = this.fs.get(path) as FsFolder;
            if (!folder) {
                folder = this.toFsFolder(fullPath);
                const baseFullPath = getDirectoryPath(fullPath);
                if (fullPath !== baseFullPath) {
                    // Add folder in the base folder
                    const baseFolder = this.ensureFolder(baseFullPath, ignoreWatch, options);
                    this.addFileOrFolderInFolder(baseFolder, folder, ignoreWatch, options);
                }
                else {
                    // root folder
                    Debug.assert(this.fs.size === 0 || !!this.windowsStyleRoot);
                    this.fs.set(path, folder);
                    this.setInode(path);
                }
            }
            Debug.assert(isFsFolder(folder));
            return folder;
        }

        private addFileOrFolderInFolder(folder: FsFolder, fileOrDirectory: FsFile | FsFolder | FsSymLink, ignoreWatch?: boolean, options?: Partial<WatchInvokeOptions>) {
            if (!this.fs.has(fileOrDirectory.path)) {
                insertSorted(folder.entries, fileOrDirectory, (a, b) => compareStringsCaseSensitive(getBaseFileName(a.path), getBaseFileName(b.path)));
            }
            folder.modifiedTime = this.now();
            this.fs.set(fileOrDirectory.path, fileOrDirectory);
            this.setInode(fileOrDirectory.path);

            if (ignoreWatch) {
                return;
            }
            const inodeWatching = this.inodeWatching;
            if (options?.skipInodeCheckOnCreate) this.inodeWatching = false;
            this.invokeFileAndFsWatches(fileOrDirectory.fullPath, FileWatcherEventKind.Created, fileOrDirectory.modifiedTime, options?.useTildeAsSuffixInRenameEventFileName);
            this.invokeFileAndFsWatches(folder.fullPath, FileWatcherEventKind.Changed, fileOrDirectory.modifiedTime, options?.useTildeAsSuffixInRenameEventFileName);
            this.inodeWatching = inodeWatching;
        }

        private removeFileOrFolder(fileOrDirectory: FsFile | FsFolder | FsSymLink, isRenaming?: boolean, options?: Partial<WatchInvokeOptions>) {
            const basePath = getDirectoryPath(fileOrDirectory.path);
            const baseFolder = this.fs.get(basePath) as FsFolder;
            if (basePath !== fileOrDirectory.path) {
                Debug.assert(!!baseFolder);
                baseFolder.modifiedTime = this.now();
                filterMutate(baseFolder.entries, entry => entry !== fileOrDirectory);
            }
            this.fs.delete(fileOrDirectory.path);

            if (isFsFolder(fileOrDirectory)) {
                Debug.assert(fileOrDirectory.entries.length === 0 || isRenaming);
            }
            if (!options?.ignoreDelete) this.invokeFileAndFsWatches(fileOrDirectory.fullPath, FileWatcherEventKind.Deleted, /*modifiedTime*/ undefined, options?.useTildeAsSuffixInRenameEventFileName);
            this.inodes?.delete(fileOrDirectory.path);
            if (!options?.ignoreDelete) this.invokeFileAndFsWatches(baseFolder.fullPath, FileWatcherEventKind.Changed, baseFolder.modifiedTime, options?.useTildeAsSuffixInRenameEventFileName);
        }

        deleteFile(filePath: string) {
            const path = this.toFullPath(filePath);
            const currentEntry = this.fs.get(path) as FsFile;
            Debug.assert(isFsFile(currentEntry));
            this.removeFileOrFolder(currentEntry);
        }

        deleteFolder(folderPath: string, recursive?: boolean) {
            const path = this.toFullPath(folderPath);
            const currentEntry = this.fs.get(path) as FsFolder;
            Debug.assert(isFsFolder(currentEntry));
            if (recursive && currentEntry.entries.length) {
                const subEntries = currentEntry.entries.slice();
                subEntries.forEach(fsEntry => {
                    if (isFsFolder(fsEntry)) {
                        this.deleteFolder(fsEntry.fullPath, recursive);
                    }
                    else {
                        this.removeFileOrFolder(fsEntry);
                    }
                });
            }
            this.removeFileOrFolder(currentEntry);
        }

        private watchFileWorker(fileName: string, cb: FileWatcherCallback, pollingInterval: PollingInterval) {
            return createWatcher(
                this.watchedFiles,
                this.toFullPath(fileName),
                { fileName, cb, pollingInterval }
            );
        }

        private fsWatchWorker(
            fileOrDirectory: string,
            recursive: boolean,
            cb: FsWatchCallback,
        ) {
            if (this.runWithFallbackPolling) throw new Error("Need to use fallback polling instead of file system native watching");
            const path = this.toFullPath(fileOrDirectory);
            // Error if the path does not exist
            if (this.inodeWatching && !this.inodes?.has(path)) throw new Error();
            const result = createWatcher(
                recursive ? this.fsWatchesRecursive : this.fsWatches,
                path,
                {
                    directoryName: fileOrDirectory,
                    cb,
                    inode: this.inodes?.get(path)
                }
            ) as FsWatchWorkerWatcher;
            result.on = noop;
            return result;
        }

        invokeFileWatcher(fileFullPath: string, eventKind: FileWatcherEventKind, modifiedTime?: Date, useFileNameInCallback?: boolean) {
            invokeWatcherCallbacks(this.watchedFiles.get(this.toPath(fileFullPath)), ({ cb, fileName }) => cb(useFileNameInCallback ? fileName : fileFullPath, eventKind, modifiedTime));
        }

        private fsWatchCallback(map: MultiMap<Path, TestFsWatcher>, fullPath: string, eventName: "rename" | "change", modifiedTime: Date | undefined, entryFullPath: string | undefined, useTildeSuffix: boolean | undefined) {
            const path = this.toPath(fullPath);
            const currentInode = this.inodes?.get(path);
            invokeWatcherCallbacks(map.get(path), ({ cb, inode }) => {
                // TODO::
                if (this.inodeWatching && inode !== undefined && inode !== currentInode) return;
                let relativeFileName = (entryFullPath ? this.getRelativePathToDirectory(fullPath, entryFullPath) : "");
                if (useTildeSuffix) relativeFileName = (relativeFileName ? relativeFileName : getBaseFileName(fullPath)) + "~";
                cb(eventName, relativeFileName, modifiedTime);
            });
        }

        invokeFsWatchesCallbacks(fullPath: string, eventName: "rename" | "change", modifiedTime?: Date, entryFullPath?: string, useTildeSuffix?: boolean) {
            this.fsWatchCallback(this.fsWatches, fullPath, eventName, modifiedTime, entryFullPath, useTildeSuffix);
        }

        invokeFsWatchesRecursiveCallbacks(fullPath: string, eventName: "rename" | "change", modifiedTime?: Date, entryFullPath?: string, useTildeSuffix?: boolean) {
            this.fsWatchCallback(this.fsWatchesRecursive, fullPath, eventName, modifiedTime, entryFullPath, useTildeSuffix);
        }

        private getRelativePathToDirectory(directoryFullPath: string, fileFullPath: string) {
            return getRelativePathToDirectoryOrUrl(directoryFullPath, fileFullPath, this.currentDirectory, this.getCanonicalFileName, /*isAbsolutePathAnUrl*/ false);
        }

        private invokeRecursiveFsWatches(fullPath: string, eventName: "rename" | "change", modifiedTime?: Date, entryFullPath?: string, useTildeSuffix?: boolean) {
            this.invokeFsWatchesRecursiveCallbacks(fullPath, eventName, modifiedTime, entryFullPath, useTildeSuffix);
            const basePath = getDirectoryPath(fullPath);
            if (this.getCanonicalFileName(fullPath) !== this.getCanonicalFileName(basePath)) {
                this.invokeRecursiveFsWatches(basePath, eventName, modifiedTime, entryFullPath || fullPath, useTildeSuffix);
            }
        }

        private invokeFsWatches(fullPath: string, eventName: "rename" | "change", modifiedTime: Date | undefined, useTildeSuffix: boolean | undefined) {
            this.invokeFsWatchesCallbacks(fullPath, eventName, modifiedTime, fullPath, useTildeSuffix);
            this.invokeFsWatchesCallbacks(getDirectoryPath(fullPath), eventName, modifiedTime, fullPath, useTildeSuffix);
            this.invokeRecursiveFsWatches(fullPath, eventName, modifiedTime, /*entryFullPath*/ undefined, useTildeSuffix);
        }

        private invokeFileAndFsWatches(fileOrFolderFullPath: string, eventKind: FileWatcherEventKind, modifiedTime?: Date, useTildeSuffix?: boolean) {
            this.invokeFileWatcher(fileOrFolderFullPath, eventKind, modifiedTime);
            this.invokeFsWatches(fileOrFolderFullPath, eventKind === FileWatcherEventKind.Changed ? "change" : "rename", modifiedTime, useTildeSuffix);
        }

        private toFsEntry(path: string): FSEntryBase {
            const fullPath = getNormalizedAbsolutePath(path, this.currentDirectory);
            return {
                path: this.toPath(fullPath),
                fullPath,
                modifiedTime: this.now()
            };
        }

        private toFsFile(file: File): FsFile {
            const fsFile = this.toFsEntry(file.path) as FsFile;
            fsFile.content = file.content;
            fsFile.fileSize = file.fileSize;
            return fsFile;
        }

        private toFsSymLink(symLink: SymLink): FsSymLink {
            const fsSymLink = this.toFsEntry(symLink.path) as FsSymLink;
            fsSymLink.symLink = getNormalizedAbsolutePath(symLink.symLink, getDirectoryPath(fsSymLink.fullPath));
            return fsSymLink;
        }

        private toFsFolder(path: string): FsFolder {
            const fsFolder = this.toFsEntry(path) as FsFolder;
            fsFolder.entries = [] as FSEntry[] as SortedArray<FSEntry>; // https://github.com/Microsoft/TypeScript/issues/19873
            return fsFolder;
        }

        private getRealFsEntry<T extends FSEntry>(isFsEntry: (fsEntry: FSEntry) => fsEntry is T, path: Path, fsEntry = this.fs.get(path)!): T | undefined {
            if (isFsEntry(fsEntry)) {
                return fsEntry;
            }

            if (isFsSymLink(fsEntry)) {
                return this.getRealFsEntry(isFsEntry, this.toPath(fsEntry.symLink));
            }

            if (fsEntry) {
                // This fs entry is something else
                return undefined;
            }

            const realpath = this.toPath(this.realpath(path));
            if (path !== realpath) {
                return this.getRealFsEntry(isFsEntry, realpath);
            }

            return undefined;
        }

        private isFsFile(fsEntry: FSEntry) {
            return !!this.getRealFile(fsEntry.path, fsEntry);
        }

        private getRealFile(path: Path, fsEntry?: FSEntry): FsFile | undefined {
            return this.getRealFsEntry(isFsFile, path, fsEntry);
        }

        private isFsFolder(fsEntry: FSEntry) {
            return !!this.getRealFolder(fsEntry.path, fsEntry);
        }

        private getRealFolder(path: Path, fsEntry = this.fs.get(path)): FsFolder | undefined {
            return this.getRealFsEntry(isFsFolder, path, fsEntry);
        }

        fileSystemEntryExists(s: string, entryKind: FileSystemEntryKind) {
            return entryKind === FileSystemEntryKind.File ? this.fileExists(s) : this.directoryExists(s);
        }

        fileExists(s: string) {
            const path = this.toFullPath(s);
            return !!this.getRealFile(path);
        }

        getModifiedTime(s: string) {
            const path = this.toFullPath(s);
            const fsEntry = this.fs.get(path);
            return (fsEntry && fsEntry.modifiedTime)!; // TODO: GH#18217
        }

        setModifiedTime(s: string, date: Date) {
            const path = this.toFullPath(s);
            const fsEntry = this.fs.get(path);
            if (fsEntry) {
                fsEntry.modifiedTime = date;
                this.invokeFileAndFsWatches(fsEntry.fullPath, FileWatcherEventKind.Changed, fsEntry.modifiedTime);
            }
        }

        readFile(s: string): string | undefined {
            const fsEntry = this.getRealFile(this.toFullPath(s));
            return fsEntry ? fsEntry.content : undefined;
        }

        getFileSize(s: string) {
            const path = this.toFullPath(s);
            const entry = this.fs.get(path)!;
            if (isFsFile(entry)) {
                return entry.fileSize ? entry.fileSize : entry.content.length;
            }
            return undefined!; // TODO: GH#18217
        }

        directoryExists(s: string) {
            const path = this.toFullPath(s);
            return !!this.getRealFolder(path);
        }

        getDirectories(s: string): string[] {
            const path = this.toFullPath(s);
            const folder = this.getRealFolder(path);
            if (folder) {
                return mapDefined(folder.entries, entry => this.isFsFolder(entry) ? getBaseFileName(entry.fullPath) : undefined);
            }
            Debug.fail(folder ? "getDirectories called on file" : "getDirectories called on missing folder");
            return [];
        }

        readDirectory(path: string, extensions?: readonly string[], exclude?: readonly string[], include?: readonly string[], depth?: number): string[] {
            return matchFiles(path, extensions, exclude, include, this.useCaseSensitiveFileNames, this.getCurrentDirectory(), depth, (dir) => {
                const directories: string[] = [];
                const files: string[] = [];
                const folder = this.getRealFolder(this.toPath(dir));
                if (folder) {
                    folder.entries.forEach((entry) => {
                        if (this.isFsFolder(entry)) {
                            directories.push(getBaseFileName(entry.fullPath));
                        }
                        else if (this.isFsFile(entry)) {
                            files.push(getBaseFileName(entry.fullPath));
                        }
                        else {
                            Debug.fail("Unknown entry");
                        }
                    });
                }
                return { directories, files };
            }, path => this.realpath(path));
        }

        createHash(s: string): string {
            return `${generateDjb2Hash(s)}-${s}`;
        }

        createSHA256Hash(s: string): string {
            return sys.createSHA256Hash!(s);
        }

        // TOOD: record and invoke callbacks to simulate timer events
        setTimeout(callback: TimeOutCallback, ms: number, ...args: any[]) {
            return this.timeoutCallbacks.register(callback, args, ms);
        }

        getNextTimeoutId() {
            return this.timeoutCallbacks.getNextId();
        }

        clearTimeout(timeoutId: any): void {
            this.timeoutCallbacks.unregister(timeoutId);
        }

        clearScreen(): void {
            this.screenClears.push(this.output.length);
        }

        checkTimeoutQueueLengthAndRun(expected: number) {
            this.checkTimeoutQueueLength(expected);
            this.runQueuedTimeoutCallbacks();
        }

        checkTimeoutQueueLength(expected: number) {
            const callbacksCount = this.timeoutCallbacks.count();
            assert.equal(callbacksCount, expected, `expected ${expected} timeout callbacks queued but found ${callbacksCount}.`);
        }

        runQueuedTimeoutCallbacks(timeoutId?: number) {
            try {
                this.timeoutCallbacks.invoke(timeoutId);
            }
            catch (e) {
                if (e.message === this.exitMessage) {
                    return;
                }
                throw e;
            }
        }

        runQueuedImmediateCallbacks(checkCount?: number) {
            if (checkCount !== undefined) {
                assert.equal(this.immediateCallbacks.count(), checkCount);
            }
            this.immediateCallbacks.invoke();
        }

        setImmediate(callback: TimeOutCallback, ...args: any[]) {
            return this.immediateCallbacks.register(callback, args);
        }

        clearImmediate(timeoutId: any): void {
            this.immediateCallbacks.unregister(timeoutId);
        }

        createDirectory(directoryName: string): void {
            const folder = this.toFsFolder(directoryName);

            // base folder has to be present
            const base = getDirectoryPath(folder.path);
            const baseFolder = this.fs.get(base) as FsFolder;
            Debug.assert(isFsFolder(baseFolder));

            Debug.assert(!this.fs.get(folder.path));
            this.addFileOrFolderInFolder(baseFolder, folder);
        }

        writeFile(path: string, content: string): void {
            const file = this.toFsFile({ path, content });

            // base folder has to be present
            const base = getDirectoryPath(file.path);
            const folder = Debug.checkDefined(this.getRealFolder(base));

            if (folder.path === base) {
                if (!this.fs.has(file.path)) {
                    this.addFileOrFolderInFolder(folder, file);
                }
                else {
                    this.modifyFile(path, content);
                }
            }
            else {
                this.writeFile(this.realpath(path), content);
            }
        }

        prependFile(path: string, content: string, options?: Partial<WatchInvokeOptions>): void {
            this.modifyFile(path, content + this.readFile(path), options);
        }

        appendFile(path: string, content: string, options?: Partial<WatchInvokeOptions>): void {
            this.modifyFile(path, this.readFile(path) + content, options);
        }

        write(message: string) {
            this.output.push(message);
        }

        getOutput(): readonly string[] {
            return this.output;
        }

        clearOutput() {
            clear(this.output);
            this.screenClears.length = 0;
        }

        serializeOutput(baseline: string[]) {
            const output = this.getOutput();
            let start = 0;
            baseline.push("Output::");
            for (const screenClear of this.screenClears) {
                baselineOutputs(baseline, output, start, screenClear);
                start = screenClear;
                baseline.push(">> Screen clear");
            }
            baselineOutputs(baseline, output, start);
            baseline.push("");
            this.clearOutput();
        }

        snap(): ESMap<Path, FSEntry> {
            const result = new Map<Path, FSEntry>();
            this.fs.forEach((value, key) => {
                const cloneValue = clone(value);
                if (isFsFolder(cloneValue)) {
                    cloneValue.entries = cloneValue.entries.map(clone) as SortedArray<FSEntry>;
                }
                result.set(key, cloneValue);
            });

            return result;
        }

        writtenFiles?: ESMap<Path, number>;
        diff(baseline: string[], base: ESMap<Path, FSEntry> = new Map()) {
            this.fs.forEach((newFsEntry, path) => {
                diffFsEntry(baseline, base.get(path), newFsEntry, this.inodes?.get(path), this.writtenFiles);
            });
            base.forEach((oldFsEntry, path) => {
                const newFsEntry = this.fs.get(path);
                if (!newFsEntry) {
                    diffFsEntry(baseline, oldFsEntry, newFsEntry, this.inodes?.get(path), this.writtenFiles);
                }
            });
            baseline.push("");
        }

        serializeWatches(baseline: string[] = []) {
            serializeMultiMap(baseline, "WatchedFiles", this.watchedFiles, ({ fileName, pollingInterval }) => ({ fileName, pollingInterval }));
            baseline.push("");
            serializeMultiMap(baseline, "FsWatches", this.fsWatches, serializeTestFsWatcher);
            baseline.push("");
            serializeMultiMap(baseline, "FsWatchesRecursive", this.fsWatchesRecursive, serializeTestFsWatcher);
            baseline.push("");
            return baseline;
        }

        realpath(s: string): string {
            const fullPath = this.toNormalizedAbsolutePath(s);
            const path = this.toPath(fullPath);
            if (getDirectoryPath(path) === path) {
                // Root
                return s;
            }
            const dirFullPath = this.realpath(getDirectoryPath(fullPath));
            const realFullPath = combinePaths(dirFullPath, getBaseFileName(fullPath));
            const fsEntry = this.fs.get(this.toPath(realFullPath))!;
            if (isFsSymLink(fsEntry)) {
                return this.realpath(fsEntry.symLink);
            }

            // realpath supports non-existent files, so there may not be an fsEntry
            return fsEntry?.fullPath || realFullPath;
        }

        readonly exitMessage = "System Exit";
        exitCode: number | undefined;
        readonly resolvePath = (s: string) => s;
        readonly getExecutingFilePath = () => this.executingFilePath;
        readonly getCurrentDirectory = () => this.currentDirectory;
        exit(exitCode?: number) {
            this.exitCode = exitCode;
            throw new Error(this.exitMessage);
        }
        getEnvironmentVariable(name: string) {
            return this.environmentVariables && this.environmentVariables.get(name) || "";
        }
    }

    function diffFsFile(baseline: string[], fsEntry: FsFile, newInode: number | undefined) {
        baseline.push(`//// [${fsEntry.fullPath}]${inodeString(newInode)}\r\n${fsEntry.content}`, "");
    }
    function diffFsSymLink(baseline: string[], fsEntry: FsSymLink, newInode: number | undefined) {
        baseline.push(`//// [${fsEntry.fullPath}] symlink(${fsEntry.symLink})${inodeString(newInode)}`);
    }
    function inodeString(inode: number | undefined) {
        return inode !== undefined ? ` Inode:: ${inode}` : "";
    }
    function diffFsEntry(baseline: string[], oldFsEntry: FSEntry | undefined, newFsEntry: FSEntry | undefined, newInode: number | undefined, writtenFiles: ESMap<string, any> | undefined): void {
        const file = newFsEntry && newFsEntry.fullPath;
        if (isFsFile(oldFsEntry)) {
            if (isFsFile(newFsEntry)) {
                if (oldFsEntry.content !== newFsEntry.content) {
                    diffFsFile(baseline, newFsEntry, newInode);
                }
                else if (oldFsEntry.modifiedTime !== newFsEntry.modifiedTime) {
                    if (oldFsEntry.fullPath !== newFsEntry.fullPath) {
                        baseline.push(`//// [${file}] file was renamed from file ${oldFsEntry.fullPath}${inodeString(newInode)}`);
                    }
                    else if (writtenFiles && !writtenFiles.has(newFsEntry.path)) {
                        baseline.push(`//// [${file}] file changed its modified time${inodeString(newInode)}`);
                    }
                    else {
                        baseline.push(`//// [${file}] file written with same contents${inodeString(newInode)}`);
                    }
                }
            }
            else {
                baseline.push(`//// [${oldFsEntry.fullPath}] deleted`);
                if (isFsSymLink(newFsEntry)) {
                    diffFsSymLink(baseline, newFsEntry, newInode);
                }
            }
        }
        else if (isFsSymLink(oldFsEntry)) {
            if (isFsSymLink(newFsEntry)) {
                if (oldFsEntry.symLink !== newFsEntry.symLink) {
                    diffFsSymLink(baseline, newFsEntry, newInode);
                }
                else if (oldFsEntry.modifiedTime !== newFsEntry.modifiedTime) {
                    if (oldFsEntry.fullPath !== newFsEntry.fullPath) {
                        baseline.push(`//// [${file}] symlink was renamed from symlink ${oldFsEntry.fullPath}${inodeString(newInode)}`);
                    }
                    else if (writtenFiles && !writtenFiles.has(newFsEntry.path)) {
                        baseline.push(`//// [${file}] symlink changed its modified time${inodeString(newInode)}`);
                    }
                    else {
                        baseline.push(`//// [${file}] symlink written with same link${inodeString(newInode)}`);
                    }
                }
            }
            else {
                baseline.push(`//// [${oldFsEntry.fullPath}] deleted symlink`);
                if (isFsFile(newFsEntry)) {
                    diffFsFile(baseline, newFsEntry, newInode);
                }
            }
        }
        else if (isFsFile(newFsEntry)) {
            diffFsFile(baseline, newFsEntry, newInode);
        }
        else if (isFsSymLink(newFsEntry)) {
            diffFsSymLink(baseline, newFsEntry, newInode);
        }
    }

    function serializeTestFsWatcher({ directoryName, inode }: TestFsWatcher) {
        return {
            directoryName,
            inode,
        };
    }

    function serializeMultiMap<T, U>(baseline: string[], caption: string, multiMap: MultiMap<string, T>, valueMapper: (value: T) => U) {
        baseline.push(`${caption}::`);
        multiMap.forEach((values, key) => {
            baseline.push(`${key}:`);
            for (const value of values) {
                baseline.push(`  ${JSON.stringify(valueMapper(value))}`);
            }
        });
    }

    function baselineOutputs(baseline: string[], output: readonly string[], start: number, end = output.length) {
        let baselinedOutput: string[] | undefined;
        for (let i = start; i < end; i++) {
            (baselinedOutput ||= []).push(output[i].replace(/Elapsed::\s[0-9]+(?:\.\d+)?ms/g, "Elapsed:: *ms"));
        }
        if (baselinedOutput) baseline.push(baselinedOutput.join(""));
    }

    export type TestServerHostTrackingWrittenFiles = TestServerHost & { writtenFiles: ESMap<Path, number>; };

    export function changeToHostTrackingWrittenFiles(inputHost: TestServerHost) {
        const host = inputHost as TestServerHostTrackingWrittenFiles;
        const originalWriteFile = host.writeFile;
        host.writtenFiles = new Map<Path, number>();
        host.writeFile = (fileName, content) => {
            originalWriteFile.call(host, fileName, content);
            const path = host.toFullPath(fileName);
            host.writtenFiles.set(path, (host.writtenFiles.get(path) || 0) + 1);
        };
        return host;
    }
    export const tsbuildProjectsLocation = "/user/username/projects";
    export function getTsBuildProjectFilePath(project: string, file: string) {
        return `${tsbuildProjectsLocation}/${project}/${file}`;
    }

    export function getTsBuildProjectFile(project: string, file: string): File {
        return {
            path: getTsBuildProjectFilePath(project, file),
            content: Harness.IO.readFile(`${Harness.IO.getWorkspaceRoot()}/tests/projects/${project}/${file}`)!
        };
    }
}