const express = require('express');
const fs = require('fs');
const path = require('path');

const router = express.Router();

const THEMES_DIR = path.join(__dirname, '..', '..', 'frontend', 'themes');

/* Surface order — themes whose folder name appears here are listed first,
   in this order. Anything else is appended alphabetically. Lets us keep
   the built-ins (nebula / dark-blue / light) at the top of the dropdown
   without hardcoding their existence in the API. */
const PREFERRED_ORDER = ['nebula', 'dark-blue', 'light'];

/* =========================
   GET /api/themes/list

   Walks frontend/themes/<name>/ and returns one entry per directory that
   contains a theme.css. Optional meta.json supplies a friendlier display
   name. No hardcoded list — built-ins live in folders just like any
   custom theme.

   Public — the list of theme names isn't sensitive and the frontend
   needs it before login to render the right palette on the login
   overlay too.
========================= */
router.get('/list', (req, res) => {
  const themes = [];
  try {
    if (fs.existsSync(THEMES_DIR)) {
      for (const entry of fs.readdirSync(THEMES_DIR, { withFileTypes: true })) {
        if (!entry.isDirectory()) continue;
        const name = entry.name;
        const cssPath = path.join(THEMES_DIR, name, 'theme.css');
        if (!fs.existsSync(cssPath)) continue;

        let displayName = name;
        let builtin = false;
        const metaPath = path.join(THEMES_DIR, name, 'meta.json');
        if (fs.existsSync(metaPath)) {
          try {
            const meta = JSON.parse(fs.readFileSync(metaPath, 'utf8'));
            if (meta && typeof meta.displayName === 'string' && meta.displayName.trim()) {
              displayName = meta.displayName.trim();
            }
            if (meta && meta.builtin === true) builtin = true;
          } catch (_) {
            /* malformed meta.json — fall back to folder name */
          }
        }

        themes.push({ name, displayName, css: `/themes/${name}/theme.css`, builtin });
      }
    }
  } catch (err) {
    console.error('Error scanning themes directory:', err);
  }

  themes.sort((a, b) => {
    const ai = PREFERRED_ORDER.indexOf(a.name);
    const bi = PREFERRED_ORDER.indexOf(b.name);
    if (ai !== -1 && bi !== -1) return ai - bi;
    if (ai !== -1) return -1;
    if (bi !== -1) return 1;
    return a.displayName.localeCompare(b.displayName);
  });

  res.json(themes);
});

module.exports = router;