feat: progressive Level-Kurve + atomarer /auth/progress-Vertrag

- levelForEp/levelInfo (Level 1 bei 20 EP statt fixer 500/Level), src/lib/leveling.js
- /auth/me liefert level + ep_into_level + ep_to_next_level
- /auth/progress liefert prev_level, streak_increased, daily_ep, daily_goal_ep, goal_just_reached
  (CTE fängt die Pre-Update-Werte, damit Level-Up/Streak-Up atomar erkennbar sind)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/leveling.js

@@ -0,0 +1,30 @@
+// Progressive Level-Kurve — Single Source of Truth fürs Backend.
+// Kumulative EP, die für Level n nötig sind: 5·n·(n+3).
+//   Level 1 → 20 EP, Level 2 → 50, Level 3 → 90, Level 4 → 140, Level 5 → 200 …
+// Früh schnelle Level (erste Level fallen in der ersten Session), danach sanft steiler.
+function epForLevel(level) {
+  if (level <= 0) return 0;
+  return 5 * level * (level + 3);
+}
+
+// Höchstes n mit 5n²+15n ≤ ep  →  n ≤ (−15 + √(225 + 20·ep)) / 10
+function levelForEp(ep) {
+  const e = Math.max(0, ep || 0);
+  return Math.floor((-15 + Math.sqrt(225 + 20 * e)) / 10);
+}
+
+// Level + Fortschritt innerhalb des Levels (für Momentum-Anzeige im Client).
+function levelInfo(ep) {
+  const e = Math.max(0, ep || 0);
+  const level = levelForEp(e);
+  const base = epForLevel(level);
+  const next = epForLevel(level + 1);
+  return {
+    level,
+    ep_into_level: e - base,
+    ep_to_next_level: next - e,
+    ep_for_next_level: next - base,
+  };
+}
+
+module.exports = { epForLevel, levelForEp, levelInfo };

src/routes/auth.js

@@ -2,6 +2,7 @@ const router = require('express').Router();
 const bcrypt = require('bcryptjs');
 const jwt = require('jsonwebtoken');
 const { query } = require('../db');
+const { levelForEp, levelInfo } = require('../lib/leveling');
 
 function signToken(user) {
   return jwt.sign(
@@ -153,7 +154,7 @@ router.get('/me', requireJwt, async (req, res, next) => {
     );
     if (!r.rows.length) return res.status(404).json({ error: 'User not found' });
     const row = r.rows[0];
-    row.level = Math.floor((row.total_ep || 0) / 500);
+    Object.assign(row, levelInfo(row.total_ep)); // level + ep_into_level + ep_to_next_level
     res.json(row);
   } catch (err) { next(err); }
 });
@@ -179,38 +180,58 @@ router.post('/progress', requireJwt, async (req, res, next) => {
       [userId, pair_id, isCorrect ? 1 : 0, isCorrect ? 0 : 1, pts]
     );
 
-    // Tagesverlauf upserten (für Streak-Kalender, Wochengraph, Tagesziel)
-    await query(
+    // Tagesverlauf upserten (für Streak-Kalender, Wochengraph, Tagesziel).
+    // RETURNING ep_earned = NEUER Tagesstand → Tagesziel-Übergang erkennbar.
+    const day = await query(
       `INSERT INTO user_daily_activity (user_id, activity_date, ep_earned, cards_done, correct_count)
        VALUES ($1, CURRENT_DATE, $2, 1, $3)
        ON CONFLICT (user_id, activity_date) DO UPDATE SET
          ep_earned     = user_daily_activity.ep_earned + $2,
          cards_done    = user_daily_activity.cards_done + 1,
-         correct_count = user_daily_activity.correct_count + $3`,
+         correct_count = user_daily_activity.correct_count + $3
+       RETURNING ep_earned`,
       [userId, pts, isCorrect ? 1 : 0]
     );
 
-    // EP + Streak auf users_public; Streak: +1 bei neuem Tag, Reset bei Lücke > 1 Tag
+    // EP + Streak auf users_public; Streak: +1 bei neuem Tag, Reset bei Lücke > 1 Tag.
+    // CTE fängt die Pre-Update-Werte mit, damit Level-Up/Streak-Up atomar erkennbar sind.
     const upd = await query(
-      `UPDATE users_public SET
-         total_ep    = total_ep + $2,
+      `WITH prev AS (
+         SELECT total_ep AS prev_ep, streak_days AS prev_streak
+           FROM users_public WHERE user_id = $1
+       )
+       UPDATE users_public up SET
+         total_ep    = up.total_ep + $2,
          streak_days = CASE
-           WHEN last_practice_at IS NULL THEN 1
-           WHEN last_practice_at::date = CURRENT_DATE THEN streak_days
-           WHEN last_practice_at::date = CURRENT_DATE - INTERVAL '1 day' THEN streak_days + 1
+           WHEN up.last_practice_at IS NULL THEN 1
+           WHEN up.last_practice_at::date = CURRENT_DATE THEN up.streak_days
+           WHEN up.last_practice_at::date = CURRENT_DATE - INTERVAL '1 day' THEN up.streak_days + 1
            ELSE 1
          END,
          last_practice_at = NOW()
-       WHERE user_id = $1
-       RETURNING total_ep, streak_days`,
+       FROM prev
+       WHERE up.user_id = $1
+       RETURNING up.total_ep, up.streak_days, up.daily_goal_ep, prev.prev_ep, prev.prev_streak`,
       [userId, pts]
     );
 
     if (!upd.rows.length)
       return res.status(409).json({ error: 'Kein Profil vorhanden. Bitte zuerst Profil anlegen.' });
 
-    const { total_ep, streak_days } = upd.rows[0];
-    res.json({ total_ep, streak_days, level: Math.floor(total_ep / 500) });
+    const r = upd.rows[0];
+    const daily_ep      = day.rows[0]?.ep_earned ?? pts;
+    const daily_goal_ep = r.daily_goal_ep || 30;
+    res.json({
+      total_ep:   r.total_ep,
+      level:      levelForEp(r.total_ep),
+      prev_level: levelForEp(r.prev_ep),
+      streak_days:      r.streak_days,
+      streak_increased: r.streak_days > r.prev_streak,
+      daily_ep,
+      daily_goal_ep,
+      // Schwellen-Übergang: jetzt erreicht, vorher (ohne diese Karte) noch nicht
+      goal_just_reached: daily_ep >= daily_goal_ep && (daily_ep - pts) < daily_goal_ep,
+    });
   } catch (err) { next(err); }
 });