import { readdir, readFile } from 'node:fs/promises';
import path from 'node:path';

// Content packs are discovered from the filesystem, so adding a theme or a
// language is just dropping files in a folder: no code change, no rebuild list.

const THEME_ID = /^[a-z0-9][a-z0-9-]*$/;
const LOCALE_CODE = /^[a-z]{2,3}(-[A-Za-z0-9]+)*$/;

async function readJson(file) {
  return JSON.parse(await readFile(file, 'utf8'));
}

async function listLocaleCodes(dir) {
  let names;
  try {
    names = await readdir(dir);
  } catch {
    return [];
  }
  return names
    .filter((n) => n.endsWith('.json'))
    .map((n) => n.slice(0, -'.json'.length))
    .filter((code) => LOCALE_CODE.test(code))
    .sort();
}

/** GET /api/themes -> [{ id, order, assets, locales }] */
async function listThemes(publicDir) {
  const root = path.join(publicDir, 'themes');
  const entries = await readdir(root, { withFileTypes: true }).catch(() => []);
  const themes = [];
  for (const entry of entries) {
    if (!entry.isDirectory() || !THEME_ID.test(entry.name)) continue;
    const dir = path.join(root, entry.name);
    try {
      const manifest = await readJson(path.join(dir, 'theme.json'));
      themes.push({
        id: entry.name,
        order: Number.isFinite(manifest.order) ? manifest.order : 100,
        assets: manifest.assets && typeof manifest.assets === 'object' ? manifest.assets : {},
        locales: await listLocaleCodes(path.join(dir, 'locales')),
      });
    } catch {
      // Skip folders without a valid theme.json rather than failing the whole list.
    }
  }
  return themes.sort((a, b) => a.order - b.order || a.id.localeCompare(b.id));
}

/** GET /api/locales -> [{ code, name }] */
async function listLocales(publicDir) {
  const dir = path.join(publicDir, 'locales');
  const out = [];
  for (const code of await listLocaleCodes(dir)) {
    try {
      const file = await readJson(path.join(dir, `${code}.json`));
      out.push({ code, name: file?.meta?.name ?? code });
    } catch {
      // Ignore malformed locale files.
    }
  }
  return out;
}

/** Returns a JSON payload for known /api routes, or undefined for unknown ones. */
export async function handleApi(publicDir, pathname) {
  switch (pathname) {
    case '/api/themes':
      return listThemes(publicDir);
    case '/api/locales':
      return listLocales(publicDir);
    default:
      return undefined;
  }
}