function routingInitialNavigationRule()

in modules/express-engine/schematics/install/index.ts [157:264]
64 lines of code
16 McCabe index (conditional complexity)

function routingInitialNavigationRule(options: UniversalOptions): Rule {
  return async (host) => {
    const project = await getProject(host, options.project);
    const serverTarget = project.targets.get('server');
    if (!serverTarget || !serverTarget.options) {
      return;
    }

    const tsConfigPath = serverTarget.options.tsConfig;
    if (!tsConfigPath || typeof tsConfigPath !== 'string' || !host.exists(tsConfigPath)) {
      // No tsconfig path
      return;
    }

    const parseConfigHost: ts.ParseConfigHost = {
      useCaseSensitiveFileNames: ts.sys.useCaseSensitiveFileNames,
      readDirectory: ts.sys.readDirectory,
      fileExists: function (fileName: string): boolean {
        return host.exists(fileName);
      },
      readFile: function (fileName: string): string {
        return host.read(fileName).toString();
      },
    };
    const { config } = ts.readConfigFile(tsConfigPath, parseConfigHost.readFile);
    const parsed = ts.parseJsonConfigFileContent(
      config,
      parseConfigHost,
      dirname(normalize(tsConfigPath)),
    );
    const tsHost = ts.createCompilerHost(parsed.options, true);
    // Strip BOM as otherwise TSC methods (Ex: getWidth) will return an offset,
    // which breaks the CLI UpdateRecorder.
    // See: https://github.com/angular/angular/pull/30719
    tsHost.readFile = function (fileName: string): string {
      return host
        .read(fileName)
        .toString()
        .replace(/^\uFEFF/, '');
    };
    tsHost.directoryExists = function (directoryName: string): boolean {
      // When the path is file getDir will throw.
      try {
        const dir = host.getDir(directoryName);

        return !!(dir.subdirs.length || dir.subfiles.length);
      } catch {
        return false;
      }
    };
    tsHost.fileExists = function (fileName: string): boolean {
      return host.exists(fileName);
    };
    tsHost.realpath = function (path: string): string {
      return path;
    };
    tsHost.getCurrentDirectory = function () {
      return host.root.path;
    };

    const program = ts.createProgram(parsed.fileNames, parsed.options, tsHost);
    const typeChecker = program.getTypeChecker();
    const sourceFiles = program
      .getSourceFiles()
      .filter((f) => !f.isDeclarationFile && !program.isSourceFileFromExternalLibrary(f));
    const printer = ts.createPrinter();
    const routerModule = 'RouterModule';
    const routerSource = '@angular/router';

    sourceFiles.forEach((sourceFile) => {
      const routerImport = findImport(sourceFile, routerSource, routerModule);
      if (!routerImport) {
        return;
      }

      let routerModuleNode: ts.CallExpression;
      ts.forEachChild(sourceFile, function visitNode(node: ts.Node) {
        if (
          ts.isCallExpression(node) &&
          ts.isPropertyAccessExpression(node.expression) &&
          ts.isIdentifier(node.expression.expression) &&
          node.expression.name.text === 'forRoot'
        ) {
          const imp = getImportOfIdentifier(typeChecker, node.expression.expression);

          if (imp && imp.name === routerModule && imp.importModule === routerSource) {
            routerModuleNode = node;
          }
        }

        ts.forEachChild(node, visitNode);
      });

      if (routerModuleNode) {
        const print = printer.printNode(
          ts.EmitHint.Unspecified,
          addInitialNavigation(routerModuleNode),
          sourceFile,
        );

        const recorder = host.beginUpdate(sourceFile.fileName);
        recorder.remove(routerModuleNode.getStart(), routerModuleNode.getWidth());
        recorder.insertRight(routerModuleNode.getStart(), print);
        host.commitUpdate(recorder);
      }
    });
  };
}