discovery.ts

/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.dev/license
 */

/**
 * @fileoverview This file contains the logic for discovering the package manager
 * used in a project by searching for lockfiles. It is designed to be efficient
 * and to correctly handle monorepo structures.
 */

import { dirname, join } from 'node:path';
import { Host } from './host';
import { Logger } from './logger';
import {
  PACKAGE_MANAGER_PRECEDENCE,
  PackageManagerName,
  SUPPORTED_PACKAGE_MANAGERS,
} from './package-manager-descriptor';

/**
 * Searches a directory for lockfiles and returns a set of package managers that correspond to them.
 * @param host A `Host` instance for interacting with the file system.
 * @param directory The directory to search.
 * @param logger An optional logger instance.
 * @returns A promise that resolves to a set of package manager names.
 */
async function findLockfiles(
  host: Host,
  directory: string,
  logger?: Logger,
): Promise<Set<PackageManagerName>> {
  logger?.debug(`Searching for lockfiles in '${directory}'...`);

  const foundPackageManagers = new Set<PackageManagerName>();
  const checks: Promise<void>[] = [];

  for (const [name, descriptor] of Object.entries(SUPPORTED_PACKAGE_MANAGERS)) {
    const manager = name as PackageManagerName;
    for (const lockfile of descriptor.lockfiles) {
      checks.push(
        (async () => {
          try {
            const path = join(directory, lockfile);
            const stats = await host.stat(path);
            if (stats.isFile()) {
              logger?.debug(`  Found '${lockfile}'.`);
              foundPackageManagers.add(manager);
            }
          } catch {
            // File does not exist or cannot be accessed.
          }
        })(),
      );
    }
  }

  await Promise.all(checks);

  return foundPackageManagers;
}

/**
 * Checks if a given path is a directory.
 * @param host A `Host` instance for interacting with the file system.
 * @param path The path to check.
 * @returns A promise that resolves to true if the path is a directory, false otherwise.
 */
async function isDirectory(host: Host, path: string): Promise<boolean> {
  try {
    return (await host.stat(path)).isDirectory();
  } catch {
    return false;
  }
}

/**
 * Discovers the package manager used in a project by searching for lockfiles.
 *
 * This function searches for lockfiles in the given directory and its ancestors.
 * If multiple lockfiles are found, it uses the precedence array to determine
 * which package manager to use. The search is bounded by the git repository root.
 *
 * @param host A `Host` instance for interacting with the file system.
 * @param startDir The directory to start the search from.
 * @param logger An optional logger instance.
 * @returns A promise that resolves to the name of the discovered package manager, or null if none is found.
 */
export async function discover(
  host: Host,
  startDir: string,
  logger?: Logger,
): Promise<PackageManagerName | null> {
  logger?.debug(`Starting package manager discovery in '${startDir}'...`);
  let currentDir = startDir;

  while (true) {
    const found = await findLockfiles(host, currentDir, logger);

    if (found.size > 0) {
      logger?.debug(`Found lockfile(s): [${[...found].join(', ')}]. Applying precedence...`);
      for (const packageManager of PACKAGE_MANAGER_PRECEDENCE) {
        if (found.has(packageManager)) {
          logger?.debug(`Selected '${packageManager}' based on precedence.`);

          return packageManager;
        }
      }
    }

    // Stop searching if we reach the git repository root.
    if (await isDirectory(host, join(currentDir, '.git'))) {
      logger?.debug(`Reached repository root at '${currentDir}'. Stopping search.`);

      return null;
    }

    const parentDir = dirname(currentDir);
    if (parentDir === currentDir) {
      // We have reached the filesystem root.
      logger?.debug('Reached filesystem root. No lockfile found.');

      return null;
    }

    currentDir = parentDir;
  }
}