import { lstat, mkdir, readdir, symlink } from "node:fs/promises";
import path from "node:path";

/**
 * Links the repository's installed dependencies into a throwaway fixture root.
 *
 * The obvious form — one directory symlink at `<fixture>/node_modules` — is
 * destructive. A fixture runs `pnpm` inside itself, pnpm does not recognise the
 * modules directory it finds there, and its purge follows the symlink and
 * deletes the *repository's* real dependencies mid-run. With `CI=true` that
 * happens without a prompt, so a test suite silently uninstalls the workspace
 * it is running in.
 *
 * `node_modules` is therefore a real directory here, and every entry inside it
 * is an individual symlink. Package resolution is unchanged, but a recursive
 * delete unlinks the fixture's own symlinks instead of walking through one link
 * into the shared tree.
 */
export async function linkFixtureNodeModules(
  fixtureRoot: string,
  sourceRoot: string = process.cwd(),
): Promise<void> {
  const source = path.join(sourceRoot, "node_modules");
  const target = path.join(fixtureRoot, "node_modules");
  await mkdir(target, { recursive: true });
  for (const entry of await readdir(source)) {
    const from = path.join(source, entry);
    const stats = await lstat(from);
    await symlink(from, path.join(target, entry), stats.isDirectory() ? "dir" : "file");
  }
}