Learn_System/backend/src/middleware/features.js

'use strict';

/**
 * Feature-flag middleware + helpers.
 *
 *   requireFeature(name)
 *     Express middleware that 404s when the GLOBAL feature flag is off.
 *     Doesn't see per-class overrides or free_student restrictions —
 *     those are layered on in computeFeaturesForUser below.
 *
 *   computeFeaturesForUser(userId, role)
 *     Synchronous merge of three sources, mirroring /api/features in
 *     server.js (kept in one place so other endpoints — gamification
 *     achievements, shop, etc. — can apply the same view of "is X
 *     enabled for THIS user right now"):
 *       1) global app_settings.feature_<name>_enabled (default = ON)
 *       2) class overlay (classes.features JSON, only `false` wins)
 *       3) free_student role overlay (app_settings.free_student_features)
 *     Returns { featureName: boolean } where boolean = is-enabled.
 *
 *   isFeatureEnabledForUser(userId, role, featureName)
 *     Thin wrapper around computeFeaturesForUser for single-feature
 *     checks. Returns true if the feature is on (or unknown — opt-in
 *     disable model).
 *
 * Usage:
 *   app.use('/api/pet', requireFeature('pet'), petRoutes);
 *   const feats = computeFeaturesForUser(userId, role);
 *   if (feats.exam9 === false) { ... }
 */
const db = require('../db/db');
const jwt = require('jsonwebtoken');

// Админ-оверрайд: requireFeature идёт ДО authMiddleware (req.user ещё нет),
// поэтому декодируем Bearer-токен сами — админ открывает и отключённые модули
// (зеркалит фронтовый _isAdminUser, см. project_gamification_killswitch).
function _isAdminReq(req) {
  try {
    const h = req.headers.authorization || '';
    if (!h.startsWith('Bearer ')) return false;
    const p = jwt.verify(h.slice(7), process.env.JWT_SECRET, { algorithms: ['HS256'] });
    return !!(p && p.role === 'admin');
  } catch (e) { return false; }
}

const _stmtSingle      = db.prepare("SELECT value FROM app_settings WHERE key = ?");
const _stmtGlobalFeats = db.prepare("SELECT key, value FROM app_settings WHERE key LIKE 'feature_%'");
const _stmtClassFeats  = db.prepare(
  'SELECT c.features FROM classes c JOIN class_members cm ON cm.class_id = c.id WHERE cm.user_id = ?'
);
const _stmtFreeStudentFeats = db.prepare("SELECT value FROM app_settings WHERE key = 'free_student_features'");

function requireFeature(name) {
  const settingKey = `feature_${name}_enabled`;
  return (req, res, next) => {
    const row = _stmtSingle.get(settingKey);
    if (row && row.value === '0' && !_isAdminReq(req)) {   // админ проходит к API даже выключенного модуля
      return res.status(404).json({ error: 'Feature disabled' });
    }
    next();
  };
}

function computeFeaturesForUser(userId, role) {
  // 1) Globals — missing = ON.
  const features = {};
  for (const r of _stmtGlobalFeats.all()) {
    const name = r.key.replace('feature_', '').replace('_enabled', '');
    features[name] = r.value === '1';
  }

  // 2) Class overlay — only `false` wins (more restrictive).
  if (userId && (role === 'student' || role === 'free_student')) {
    for (const row of _stmtClassFeats.all(userId)) {
      if (!row.features) continue;
      try {
        const f = JSON.parse(row.features);
        for (const [key, val] of Object.entries(f)) {
          if (val === false) features[key] = false;
        }
      } catch { /* malformed JSON — ignore */ }
    }
  }

  // 3) free_student overlay.
  if (role === 'free_student') {
    const fsRow = _stmtFreeStudentFeats.get();
    if (fsRow?.value) {
      try {
        const fsFeats = JSON.parse(fsRow.value);
        for (const [key, val] of Object.entries(fsFeats)) {
          if (val === false) features[key] = false;
        }
      } catch { /* malformed — ignore */ }
    }
  }
  return features;
}

function isFeatureEnabledForUser(userId, role, featureName) {
  if (!featureName) return true;
  const feats = computeFeaturesForUser(userId, role);
  // Missing key (no row in app_settings) → treat as ON (opt-in disable).
  return feats[featureName] !== false;
}

module.exports = { requireFeature, computeFeaturesForUser, isFeatureEnabledForUser };