servicesHost.ts

import * as path from 'path';
import * as typescript from 'typescript';
import * as webpack from 'webpack';

import { getParsedCommandLine } from './config';
import * as constants from './constants';
import {
  CustomResolveModuleName,
  CustomResolveTypeReferenceDirective,
  FormatDiagnosticsHost,
  ModuleResolutionHost,
  ResolvedModule,
  ResolveSync,
  SolutionBuilderWithWatchHost,
  SolutionDiagnostics,
  TSFile,
  TSInstance,
  WatchCallbacks,
  WatchFactory,
  WatchHost,
  WebpackError
} from './interfaces';
import * as logger from './logger';
import { makeResolver } from './resolver';
import { formatErrors, readFile, unorderedRemoveItem } from './utils';

export type Action = () => void;

export interface ServiceHostWhichMayBeCacheable {
  servicesHost: typescript.LanguageServiceHost;
  clearCache: Action | null;
}

/**
 * Create the TypeScript language service
 */
export function makeServicesHost(
  scriptRegex: RegExp,
  log: logger.Logger,
  loader: webpack.loader.LoaderContext,
  instance: TSInstance,
  enableFileCaching: boolean,
  projectReferences?: ReadonlyArray<typescript.ProjectReference>
): ServiceHostWhichMayBeCacheable {
  const {
    compiler,
    compilerOptions,
    appendTsTsxSuffixesIfRequired,
    files,
    loaderOptions: {
      resolveModuleName: customResolveModuleName,
      resolveTypeReferenceDirective: customResolveTypeReferenceDirective
    }
  } = instance;

  const newLine =
    compilerOptions.newLine === constants.CarriageReturnLineFeedCode
      ? constants.CarriageReturnLineFeed
      : compilerOptions.newLine === constants.LineFeedCode
      ? constants.LineFeed
      : constants.EOL;

  // make a (sync) resolver that follows webpack's rules
  const resolveSync = makeResolver(loader._compiler.options);

  const readFileWithFallback = (
    filePath: string,
    encoding?: string | undefined
  ): string | undefined =>
    compiler.sys.readFile(filePath, encoding) || readFile(filePath, encoding);

  const fileExists = (filePathToCheck: string) =>
    compiler.sys.fileExists(filePathToCheck) ||
    readFile(filePathToCheck) !== undefined;

  let clearCache: Action | null = null;
  let moduleResolutionHost: ModuleResolutionHost = {
    fileExists,
    readFile: readFileWithFallback,
    realpath: compiler.sys.realpath,
    directoryExists: compiler.sys.directoryExists,
    getCurrentDirectory: compiler.sys.getCurrentDirectory,
    getDirectories: compiler.sys.getDirectories
  };

  if (enableFileCaching) {
    const cached = addCache(moduleResolutionHost);
    clearCache = cached.clearCache;
    moduleResolutionHost = cached.moduleResolutionHost;
  }

  // loader.context seems to work fine on Linux / Mac regardless causes problems for @types resolution on Windows for TypeScript < 2.3
  const getCurrentDirectory = () => loader.context;

  const resolvers = makeResolvers(
    compiler,
    compilerOptions,
    moduleResolutionHost,
    customResolveTypeReferenceDirective,
    customResolveModuleName,
    resolveSync,
    appendTsTsxSuffixesIfRequired,
    scriptRegex,
    instance
  );

  const servicesHost: typescript.LanguageServiceHost = {
    getProjectVersion: () => `${instance.version}`,

    getProjectReferences: () => projectReferences,

    getScriptFileNames: () =>
      [...files.keys()].filter(filePath => filePath.match(scriptRegex)),

    getScriptVersion: (fileName: string) => {
      fileName = path.normalize(fileName);
      const file = files.get(fileName);
      return file === undefined ? '' : file.version.toString();
    },

    getScriptSnapshot: (fileName: string) => {
      // This is called any time TypeScript needs a file's text
      // We either load from memory or from disk
      fileName = path.normalize(fileName);
      let file = files.get(fileName);

      if (file === undefined) {
        const text = readFile(fileName);
        if (text === undefined) {
          return undefined;
        }

        file = { version: 0, text };
        files.set(fileName, file);
      }

      return compiler.ScriptSnapshot.fromString(file.text!);
    },

    /**
     * getDirectories is also required for full import and type reference completions.
     * Without it defined, certain completions will not be provided
     */
    getDirectories: compiler.sys.getDirectories,

    /**
     * For @types expansion, these two functions are needed.
     */
    directoryExists: moduleResolutionHost.directoryExists,

    useCaseSensitiveFileNames: () => compiler.sys.useCaseSensitiveFileNames,

    realpath: moduleResolutionHost.realpath,

    // The following three methods are necessary for @types resolution from TS 2.4.1 onwards see: https://github.com/Microsoft/TypeScript/issues/16772
    fileExists: moduleResolutionHost.fileExists,
    readFile: moduleResolutionHost.readFile,
    readDirectory: compiler.sys.readDirectory,

    getCurrentDirectory,

    getCompilationSettings: () => compilerOptions,
    getDefaultLibFileName: (options: typescript.CompilerOptions) =>
      compiler.getDefaultLibFilePath(options),
    getNewLine: () => newLine,
    trace: log.log,
    log: log.log,

    // used for (/// <reference types="...">) see https://github.com/Realytics/fork-ts-checker-webpack-plugin/pull/250#issuecomment-485061329
    resolveTypeReferenceDirectives: resolvers.resolveTypeReferenceDirectives,

    resolveModuleNames: resolvers.resolveModuleNames,

    getCustomTransformers: () => instance.transformers
  };

  return { servicesHost, clearCache };
}

function makeResolvers(
  compiler: typeof typescript,
  compilerOptions: typescript.CompilerOptions,
  moduleResolutionHost: typescript.ModuleResolutionHost,
  customResolveTypeReferenceDirective: CustomResolveTypeReferenceDirective,
  customResolveModuleName: CustomResolveModuleName,
  resolveSync: ResolveSync,
  appendTsTsxSuffixesIfRequired: (filePath: string) => string,
  scriptRegex: RegExp,
  instance: TSInstance
) {
  const resolveTypeReferenceDirective = makeResolveTypeReferenceDirective(
    compiler,
    compilerOptions,
    moduleResolutionHost,
    customResolveTypeReferenceDirective
  );

  const resolveTypeReferenceDirectives = (
    typeDirectiveNames: string[],
    containingFile: string,
    _redirectedReference?: typescript.ResolvedProjectReference
  ): (typescript.ResolvedTypeReferenceDirective | undefined)[] =>
    typeDirectiveNames.map(
      directive =>
        resolveTypeReferenceDirective(
          directive,
          containingFile,
          _redirectedReference
        ).resolvedTypeReferenceDirective
    );

  const resolveModuleName = makeResolveModuleName(
    compiler,
    compilerOptions,
    moduleResolutionHost,
    customResolveModuleName
  );

  const resolveModuleNames = (
    moduleNames: string[],
    containingFile: string,
    _reusedNames?: string[] | undefined,
    _redirectedReference?: typescript.ResolvedProjectReference | undefined
  ): (typescript.ResolvedModule | undefined)[] => {
    const resolvedModules = moduleNames.map(moduleName =>
      resolveModule(
        resolveSync,
        resolveModuleName,
        appendTsTsxSuffixesIfRequired,
        scriptRegex,
        moduleName,
        containingFile
      )
    );

    populateDependencyGraphs(resolvedModules, instance, containingFile);

    return resolvedModules;
  };

  return {
    resolveTypeReferenceDirectives,
    resolveModuleNames
  };
}

function createWatchFactory(
  beforeCallbacks?: (
    key: string,
    cb: typescript.FileWatcherCallback[] | typescript.DirectoryWatcherCallback[]
  ) => void
): WatchFactory {
  const watchedFiles: WatchCallbacks<
    typescript.FileWatcherCallback
  > = new Map();
  const watchedDirectories: WatchCallbacks<
    typescript.DirectoryWatcherCallback
  > = new Map();
  const watchedDirectoriesRecursive: WatchCallbacks<
    typescript.DirectoryWatcherCallback
  > = new Map();

  return {
    watchedFiles,
    watchedDirectories,
    watchedDirectoriesRecursive,
    invokeFileWatcher,
    invokeDirectoryWatcher,
    watchFile,
    watchDirectory
  };

  function invokeWatcherCallbacks(
    map:
      | Map<string, typescript.FileWatcherCallback[]>
      | Map<string, typescript.DirectoryWatcherCallback[]>,
    key: string,
    fileName: string,
    eventKind?: typescript.FileWatcherEventKind
  ) {
    const callbacks = map.get(key);
    if (callbacks !== undefined && callbacks.length) {
      // 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();
      if (beforeCallbacks) {
        beforeCallbacks(key, cbs);
      }
      for (const cb of cbs) {
        cb(fileName, eventKind as typescript.FileWatcherEventKind);
      }
    }
  }

  function invokeFileWatcher(
    fileName: string,
    eventKind: typescript.FileWatcherEventKind
  ) {
    fileName = path.normalize(fileName);
    invokeWatcherCallbacks(watchedFiles, fileName, fileName, eventKind);
  }

  function invokeDirectoryWatcher(
    directory: string,
    fileAddedOrRemoved: string
  ) {
    directory = path.normalize(directory);
    invokeWatcherCallbacks(watchedDirectories, directory, fileAddedOrRemoved);
    invokeRecursiveDirectoryWatcher(directory, fileAddedOrRemoved);
  }

  function invokeRecursiveDirectoryWatcher(
    directory: string,
    fileAddedOrRemoved: string
  ) {
    directory = path.normalize(directory);
    invokeWatcherCallbacks(
      watchedDirectoriesRecursive,
      directory,
      fileAddedOrRemoved
    );
    const basePath = path.dirname(directory);
    if (directory !== basePath) {
      invokeRecursiveDirectoryWatcher(basePath, fileAddedOrRemoved);
    }
  }

  function createWatcher<T>(
    file: string,
    callbacks: WatchCallbacks<T>,
    callback: T
  ): typescript.FileWatcher {
    file = path.normalize(file);
    const existing = callbacks.get(file);
    if (existing === undefined) {
      callbacks.set(file, [callback]);
    } else {
      existing.push(callback);
    }
    return {
      close: () => {
        // tslint:disable-next-line:no-shadowed-variable
        const existing = callbacks.get(file);
        if (existing !== undefined) {
          unorderedRemoveItem(existing, callback);
          if (!existing.length) {
            callbacks.delete(file);
          }
        }
      }
    };
  }

  function watchFile(
    fileName: string,
    callback: typescript.FileWatcherCallback,
    _pollingInterval?: number
  ) {
    return createWatcher(fileName, watchedFiles, callback);
  }

  function watchDirectory(
    fileName: string,
    callback: typescript.DirectoryWatcherCallback,
    recursive?: boolean
  ) {
    return createWatcher(
      fileName,
      recursive === true ? watchedDirectoriesRecursive : watchedDirectories,
      callback
    );
  }
}

export function updateFileWithText(
  instance: TSInstance,
  filePath: string,
  text: (nFilePath: string) => string
) {
  const nFilePath = path.normalize(filePath);
  const file =
    instance.files.get(nFilePath) || instance.otherFiles.get(nFilePath);
  if (file !== undefined) {
    const newText = text(nFilePath);
    if (newText !== file.text) {
      file.text = newText;
      file.version++;
      instance.version!++;
      if (!instance.modifiedFiles) {
        instance.modifiedFiles = new Map<string, TSFile>();
      }
      instance.modifiedFiles.set(nFilePath, file);
      if (instance.watchHost !== undefined) {
        instance.watchHost.invokeFileWatcher(
          nFilePath,
          instance.compiler.FileWatcherEventKind.Changed
        );
      }
      if (instance.solutionBuilderHost !== undefined) {
        instance.solutionBuilderHost.invokeFileWatcher(
          nFilePath,
          instance.compiler.FileWatcherEventKind.Changed
        );
      }
    }
  }
}

/**
 * Create the TypeScript Watch host
 */
export function makeWatchHost(
  scriptRegex: RegExp,
  log: logger.Logger,
  loader: webpack.loader.LoaderContext,
  instance: TSInstance,
  projectReferences?: ReadonlyArray<typescript.ProjectReference>
) {
  const {
    compiler,
    compilerOptions,
    appendTsTsxSuffixesIfRequired,
    files,
    otherFiles,
    loaderOptions: {
      resolveModuleName: customResolveModuleName,
      resolveTypeReferenceDirective: customResolveTypeReferenceDirective
    }
  } = instance;

  const newLine =
    compilerOptions.newLine === constants.CarriageReturnLineFeedCode
      ? constants.CarriageReturnLineFeed
      : compilerOptions.newLine === constants.LineFeedCode
      ? constants.LineFeed
      : constants.EOL;

  // make a (sync) resolver that follows webpack's rules
  const resolveSync = makeResolver(loader._compiler.options);

  const readFileWithFallback = (
    filePath: string,
    encoding?: string | undefined
  ): string | undefined =>
    compiler.sys.readFile(filePath, encoding) || readFile(filePath, encoding);

  const moduleResolutionHost: ModuleResolutionHost = {
    fileExists,
    readFile: readFileWithFallback,
    realpath: compiler.sys.realpath
  };

  // loader.context seems to work fine on Linux / Mac regardless causes problems for @types resolution on Windows for TypeScript < 2.3
  const getCurrentDirectory = () => loader.context;

  const {
    watchFile,
    watchDirectory,
    invokeFileWatcher,
    invokeDirectoryWatcher
  } = createWatchFactory();
  const resolvers = makeResolvers(
    compiler,
    compilerOptions,
    moduleResolutionHost,
    customResolveTypeReferenceDirective,
    customResolveModuleName,
    resolveSync,
    appendTsTsxSuffixesIfRequired,
    scriptRegex,
    instance
  );

  const watchHost: WatchHost = {
    rootFiles: getRootFileNames(),
    options: compilerOptions,

    useCaseSensitiveFileNames: () => compiler.sys.useCaseSensitiveFileNames,
    getNewLine: () => newLine,
    getCurrentDirectory,
    getDefaultLibFileName: options => compiler.getDefaultLibFilePath(options),

    fileExists,
    readFile: readFileWithCachingText,
    directoryExists: dirPath =>
      compiler.sys.directoryExists(path.normalize(dirPath)),
    getDirectories: dirPath =>
      compiler.sys.getDirectories(path.normalize(dirPath)),
    readDirectory: (dirPath, extensions, exclude, include, depth) =>
      compiler.sys.readDirectory(
        path.normalize(dirPath),
        extensions,
        exclude,
        include,
        depth
      ),
    realpath: dirPath => compiler.sys.resolvePath(path.normalize(dirPath)),
    trace: logData => log.log(logData),

    watchFile,
    watchDirectory,

    // used for (/// <reference types="...">) see https://github.com/Realytics/fork-ts-checker-webpack-plugin/pull/250#issuecomment-485061329
    resolveTypeReferenceDirectives: resolvers.resolveTypeReferenceDirectives,

    resolveModuleNames: resolvers.resolveModuleNames,

    invokeFileWatcher,
    invokeDirectoryWatcher,
    updateRootFileNames: () => {
      instance.changedFilesList = false;
      if (instance.watchOfFilesAndCompilerOptions !== undefined) {
        instance.watchOfFilesAndCompilerOptions.updateRootFileNames(
          getRootFileNames()
        );
      }
    },
    createProgram:
      projectReferences === undefined
        ? compiler.createAbstractBuilder
        : createBuilderProgramWithReferences
  };
  return watchHost;

  function getRootFileNames() {
    return [...files.keys()].filter(filePath => filePath.match(scriptRegex));
  }

  function readFileWithCachingText(fileName: string, encoding?: string) {
    fileName = path.normalize(fileName);
    const file = files.get(fileName) || otherFiles.get(fileName);
    if (file !== undefined) {
      return file.text;
    }
    const text = readFileWithFallback(fileName, encoding);
    if (text === undefined) {
      return undefined;
    }
    otherFiles.set(fileName, { version: 0, text });
    return text;
  }

  function fileExists(fileName: string) {
    const filePath = path.normalize(fileName);
    return files.has(filePath) || compiler.sys.fileExists(filePath);
  }

  function createBuilderProgramWithReferences(
    rootNames: ReadonlyArray<string> | undefined,
    options: typescript.CompilerOptions | undefined,
    host: typescript.CompilerHost | undefined,
    oldProgram: typescript.BuilderProgram | undefined,
    configFileParsingDiagnostics:
      | ReadonlyArray<typescript.Diagnostic>
      | undefined
  ) {
    const program = compiler.createProgram({
      rootNames: rootNames!,
      options: options!,
      host,
      oldProgram: oldProgram && oldProgram.getProgram(),
      configFileParsingDiagnostics,
      projectReferences
    });

    const builderProgramHost: typescript.BuilderProgramHost = host!;
    return compiler.createAbstractBuilder(
      program,
      builderProgramHost,
      oldProgram,
      configFileParsingDiagnostics
    );
  }
}

/**
 * Create the TypeScript Watch host
 */
export function makeSolutionBuilderHost(
  scriptRegex: RegExp,
  log: logger.Logger,
  loader: webpack.loader.LoaderContext,
  instance: TSInstance
): SolutionBuilderWithWatchHost {
  const {
    compiler,
    compilerOptions,
    appendTsTsxSuffixesIfRequired,
    loaderOptions: {
      resolveModuleName: customResolveModuleName,
      resolveTypeReferenceDirective: customResolveTypeReferenceDirective,
      transpileOnly
    }
  } = instance;

  // loader.context seems to work fine on Linux / Mac regardless causes problems for @types resolution on Windows for TypeScript < 2.3
  const getCurrentDirectory = () => loader.context;
  const formatDiagnosticHost: FormatDiagnosticsHost = {
    getCurrentDirectory: compiler.sys.getCurrentDirectory,
    getCanonicalFileName: compiler.sys.useCaseSensitiveFileNames
      ? s => s
      : s => s.toLowerCase(),
    getNewLine: () => compiler.sys.newLine
  };

  const diagnostics: SolutionDiagnostics = {
    global: [],
    perFile: new Map(),
    transpileErrors: []
  };
  const reportDiagnostic = (d: typescript.Diagnostic) => {
    if (transpileOnly) {
      const filePath = d.file ? path.resolve(d.file.fileName) : undefined;
      const last =
        diagnostics.transpileErrors[diagnostics.transpileErrors.length - 1];
      if (diagnostics.transpileErrors.length && last[0] === filePath) {
        last[1].push(d);
      } else {
        diagnostics.transpileErrors.push([filePath, [d]]);
      }
    } else if (d.file) {
      const filePath = path.resolve(d.file.fileName);
      const existing = diagnostics.perFile.get(filePath);
      if (existing) {
        existing.push(d);
      } else {
        diagnostics.perFile.set(filePath, [d]);
      }
    } else {
      diagnostics.global.push(d);
    }
    log.logInfo(compiler.formatDiagnostic(d, formatDiagnosticHost));
  };

  const reportSolutionBuilderStatus = (d: typescript.Diagnostic) =>
    log.logInfo(compiler.formatDiagnostic(d, formatDiagnosticHost));
  const reportWatchStatus = (
    d: typescript.Diagnostic,
    newLine: string,
    _options: typescript.CompilerOptions
  ) =>
    log.logInfo(
      `${compiler.flattenDiagnosticMessageText(
        d.messageText,
        compiler.sys.newLine
      )}${newLine + newLine}`
    );
  const solutionBuilderHost: SolutionBuilderWithWatchHost = {
    ...compiler.createSolutionBuilderWithWatchHost(
      compiler.sys,
      compiler.createEmitAndSemanticDiagnosticsBuilderProgram,
      reportDiagnostic,
      reportSolutionBuilderStatus,
      reportWatchStatus
    ),
    diagnostics,
    ...createWatchFactory(beforeWatchCallbacks),
    // Overrides
    getCurrentDirectory,
    writeFile: (name, text, writeByteOrderMark) => {
      compiler.sys.writeFile(name, text, writeByteOrderMark);
      updateFileWithText(instance, name, () => text);
    },
    setTimeout: undefined,
    clearTimeout: undefined
  };
  solutionBuilderHost.trace = logData => log.logInfo(logData);
  solutionBuilderHost.getParsedCommandLine = file =>
    getParsedCommandLine(compiler, instance.loaderOptions, file);

  // make a (sync) resolver that follows webpack's rules
  const resolveSync = makeResolver(loader._compiler.options);
  const resolvers = makeResolvers(
    compiler,
    compilerOptions,
    solutionBuilderHost,
    customResolveTypeReferenceDirective,
    customResolveModuleName,
    resolveSync,
    appendTsTsxSuffixesIfRequired,
    scriptRegex,
    instance
  );
  // used for (/// <reference types="...">) see https://github.com/Realytics/fork-ts-checker-webpack-plugin/pull/250#issuecomment-485061329
  solutionBuilderHost.resolveTypeReferenceDirectives =
    resolvers.resolveTypeReferenceDirectives;
  solutionBuilderHost.resolveModuleNames = resolvers.resolveModuleNames;

  return solutionBuilderHost;

  function beforeWatchCallbacks() {
    diagnostics.global.length = 0;
    diagnostics.perFile.clear();
    diagnostics.transpileErrors.length = 0;
  }
}

export function getSolutionErrors(instance: TSInstance, context: string) {
  const solutionErrors: WebpackError[] = [];
  if (
    instance.solutionBuilderHost &&
    instance.solutionBuilderHost.diagnostics.transpileErrors.length
  ) {
    instance.solutionBuilderHost.diagnostics.transpileErrors.forEach(
      ([filePath, errors]) =>
        solutionErrors.push(
          ...formatErrors(
            errors,
            instance.loaderOptions,
            instance.colors,
            instance.compiler,
            { file: filePath ? undefined : 'tsconfig.json' },
            context
          )
        )
    );
  }
  return solutionErrors;
}

type ResolveTypeReferenceDirective = (
  directive: string,
  containingFile: string,
  redirectedReference?: typescript.ResolvedProjectReference
) => typescript.ResolvedTypeReferenceDirectiveWithFailedLookupLocations;

function makeResolveTypeReferenceDirective(
  compiler: typeof typescript,
  compilerOptions: typescript.CompilerOptions,
  moduleResolutionHost: ModuleResolutionHost,
  customResolveTypeReferenceDirective:
    | CustomResolveTypeReferenceDirective
    | undefined
): ResolveTypeReferenceDirective {
  if (customResolveTypeReferenceDirective === undefined) {
    return (directive, containingFile, redirectedReference) =>
      compiler.resolveTypeReferenceDirective(
        directive,
        containingFile,
        compilerOptions,
        moduleResolutionHost,
        redirectedReference
      );
  }

  return (directive, containingFile) =>
    customResolveTypeReferenceDirective(
      directive,
      containingFile,
      compilerOptions,
      moduleResolutionHost,
      compiler.resolveTypeReferenceDirective
    );
}

function isJsImplementationOfTypings(
  resolvedModule: ResolvedModule,
  tsResolution: ResolvedModule
) {
  return (
    resolvedModule.resolvedFileName.endsWith('js') &&
    /\.d\.ts$/.test(tsResolution.resolvedFileName)
  );
}

function resolveModule(
  resolveSync: ResolveSync,
  resolveModuleName: ResolveModuleName,
  appendTsTsxSuffixesIfRequired: (filePath: string) => string,
  scriptRegex: RegExp,
  moduleName: string,
  containingFile: string
) {
  let resolutionResult: ResolvedModule;

  try {
    const originalFileName = resolveSync(
      undefined,
      path.normalize(path.dirname(containingFile)),
      moduleName
    );

    const resolvedFileName = appendTsTsxSuffixesIfRequired(originalFileName);

    if (resolvedFileName.match(scriptRegex) !== null) {
      resolutionResult = { resolvedFileName, originalFileName };
    }
    // tslint:disable-next-line:no-empty
  } catch (e) {}

  const tsResolution = resolveModuleName(moduleName, containingFile);

  if (tsResolution.resolvedModule !== undefined) {
    const resolvedFileName = path.normalize(
      tsResolution.resolvedModule.resolvedFileName
    );
    const tsResolutionResult: ResolvedModule = {
      originalFileName: resolvedFileName,
      resolvedFileName,
      isExternalLibraryImport:
        tsResolution.resolvedModule.isExternalLibraryImport
    };

    return resolutionResult! === undefined ||
      resolutionResult.resolvedFileName ===
        tsResolutionResult.resolvedFileName ||
      isJsImplementationOfTypings(resolutionResult!, tsResolutionResult)
      ? tsResolutionResult
      : resolutionResult!;
  }
  return resolutionResult!;
}

type ResolveModuleName = (
  moduleName: string,
  containingFile: string
) => typescript.ResolvedModuleWithFailedLookupLocations;

function makeResolveModuleName(
  compiler: typeof typescript,
  compilerOptions: typescript.CompilerOptions,
  moduleResolutionHost: ModuleResolutionHost,
  customResolveModuleName: CustomResolveModuleName | undefined
): ResolveModuleName {
  if (customResolveModuleName === undefined) {
    return (moduleName: string, containingFile: string) =>
      compiler.resolveModuleName(
        moduleName,
        containingFile,
        compilerOptions,
        moduleResolutionHost
      );
  }

  return (moduleName: string, containingFile: string) =>
    customResolveModuleName(
      moduleName,
      containingFile,
      compilerOptions,
      moduleResolutionHost,
      compiler.resolveModuleName
    );
}

function populateDependencyGraphs(
  resolvedModules: ResolvedModule[],
  instance: TSInstance,
  containingFile: string
) {
  resolvedModules = resolvedModules.filter(
    mod => mod !== null && mod !== undefined
  );

  instance.dependencyGraph[path.normalize(containingFile)] = resolvedModules;

  resolvedModules.forEach(resolvedModule => {
    if (
      instance.reverseDependencyGraph[resolvedModule.resolvedFileName] ===
      undefined
    ) {
      instance.reverseDependencyGraph[resolvedModule.resolvedFileName] = {};
    }
    instance.reverseDependencyGraph[resolvedModule.resolvedFileName]![
      path.normalize(containingFile)
    ] = true;
  });
}

function addCache(
  servicesHost: typescript.ModuleResolutionHost
): {
  moduleResolutionHost: typescript.ModuleResolutionHost;
  clearCache: () => void;
} {
  const clearCacheFunctions: Action[] = [];
  return {
    moduleResolutionHost: {
      ...servicesHost,
      fileExists: createCache(servicesHost.fileExists),
      directoryExists:
        servicesHost.directoryExists &&
        createCache(servicesHost.directoryExists),
      realpath: servicesHost.realpath && createCache(servicesHost.realpath)
    },
    clearCache: () => clearCacheFunctions.forEach(clear => clear())
  };

  function createCache<TOut>(originalFunction: (arg: string) => TOut) {
    const cache = new Map<string, TOut>();
    clearCacheFunctions.push(() => cache.clear());
    return function getCached(arg: string) {
      let res = cache.get(arg);
      if (res !== undefined) {
        return res;
      }

      res = originalFunction(arg);
      cache.set(arg, res);
      return res;
    };
  }
}