angular-cli/packages/@angular/cli/utilities/resolve-module-file.ts

import * as path from 'path';
import * as fs from 'fs';
import { dynamicPathParser } from './dynamic-path-parser';

export function resolveModulePath(
  moduleNameFromFlag: string, project: any, projectRoot: any, appConfig: any): string {
  let baseModuleName = moduleNameFromFlag;
  let parentFolders = '';

  if (baseModuleName.includes(path.sep)) {
    const splitPath = baseModuleName.split(path.sep);
    baseModuleName = splitPath.pop();
    parentFolders = splitPath.join(path.sep);
  }

  if (baseModuleName.includes('.')) {
    baseModuleName = baseModuleName
      .split('.')
      .filter(part => part !== 'module' && part !== 'ts')
      .join('.');
  }

  const baseModuleWithFileSuffix = `${baseModuleName}.module.ts`;

  const moduleRelativePath = path.join(parentFolders, baseModuleWithFileSuffix);
  let fullModulePath = buildFullPath(project, moduleRelativePath, appConfig, projectRoot);

  if (!fs.existsSync(fullModulePath)) {
    const moduleWithFolderPrefix =
      path.join(parentFolders, baseModuleName, baseModuleWithFileSuffix);
    fullModulePath = buildFullPath(project, moduleWithFolderPrefix, appConfig, projectRoot);
  }

  if (!fs.existsSync(fullModulePath)) {
    throw 'Specified module does not exist';
  }

  return fullModulePath;
}

function buildFullPath(project: any, relativeModulePath: string, appConfig: any, projectRoot: any) {
  const parsedPath = dynamicPathParser(project, relativeModulePath, appConfig);
  const fullModulePath = path.join(projectRoot, parsedPath.dir, parsedPath.base);

  return fullModulePath;
}