feat(vocab): enhance lesson state management and persistence in VocabLessonView

- Added a new JSONB field `lessonState` to the VocabCourseProgress model to store detailed lesson state information.
- Implemented methods in VocabService for sanitizing and serializing lesson state, ensuring robust data handling.
- Updated VocabLessonView to manage lesson state persistence, including local storage and server synchronization, improving user experience during vocabulary lessons.
- Introduced mechanisms for exporting and normalizing exercise answers, enhancing the accuracy of saved progress.

backend/services/vocabService.js

@@ -15,6 +15,181 @@ import { Op } from 'sequelize';
 import { BISAYA_PHASE1_DIDACTICS } from '../scripts/bisaya-course-phase1.js';
 
 export default class VocabService {
+  _clampInteger(value, { min = 0, max = 100000, fallback = 0 } = {}) {
+    const numeric = Number(value);
+    if (!Number.isFinite(numeric)) {
+      return fallback;
+    }
+    return Math.max(min, Math.min(max, Math.trunc(numeric)));
+  }
+
+  _sanitizeShortString(value, maxLength = 400) {
+    const text = String(value ?? '').trim();
+    if (!text) {
+      return '';
+    }
+    return text.slice(0, maxLength);
+  }
+
+  _sanitizeStringArray(value, { maxItems = 12, maxLength = 400, keepEmpty = false } = {}) {
+    if (!Array.isArray(value)) {
+      return [];
+    }
+    return value
+      .slice(0, maxItems)
+      .map((entry) => this._sanitizeShortString(entry, maxLength))
+      .filter((entry) => keepEmpty || Boolean(entry));
+  }
+
+  _sanitizeExerciseAnswers(value) {
+    if (!value || typeof value !== 'object' || Array.isArray(value)) {
+      return {};
+    }
+
+    const sanitized = {};
+    Object.entries(value).slice(0, 200).forEach(([exerciseId, answer]) => {
+      if (!/^\d+$/.test(String(exerciseId))) {
+        return;
+      }
+      if (Array.isArray(answer)) {
+        sanitized[exerciseId] = this._sanitizeStringArray(answer, {
+          maxItems: 12,
+          maxLength: 200,
+          keepEmpty: true
+        });
+        return;
+      }
+      if (typeof answer === 'string') {
+        sanitized[exerciseId] = this._sanitizeShortString(answer, 200);
+        return;
+      }
+      if (typeof answer === 'number' && Number.isFinite(answer)) {
+        sanitized[exerciseId] = Math.trunc(answer);
+      }
+    });
+
+    return sanitized;
+  }
+
+  _sanitizeExerciseResults(value) {
+    if (!value || typeof value !== 'object' || Array.isArray(value)) {
+      return {};
+    }
+
+    const sanitized = {};
+    Object.entries(value).slice(0, 200).forEach(([exerciseId, result]) => {
+      if (!/^\d+$/.test(String(exerciseId)) || !result || typeof result !== 'object' || Array.isArray(result)) {
+        return;
+      }
+
+      sanitized[exerciseId] = {
+        correct: Boolean(result.correct),
+        correctAnswer: this._sanitizeShortString(result.correctAnswer, 400),
+        alternatives: this._sanitizeStringArray(result.alternatives, { maxItems: 8, maxLength: 200 }),
+        explanation: this._sanitizeShortString(result.explanation, 1200)
+      };
+    });
+
+    return sanitized;
+  }
+
+  _sanitizeVocabTrainerStats(value) {
+    if (!value || typeof value !== 'object' || Array.isArray(value)) {
+      return {};
+    }
+
+    const sanitized = {};
+    Object.entries(value).slice(0, 400).forEach(([key, stats]) => {
+      const safeKey = this._sanitizeShortString(key, 200);
+      if (!safeKey || !stats || typeof stats !== 'object' || Array.isArray(stats)) {
+        return;
+      }
+
+      sanitized[safeKey] = {
+        attempts: this._clampInteger(stats.attempts, { max: 5000 }),
+        correct: this._clampInteger(stats.correct, { max: 5000 }),
+        wrong: this._clampInteger(stats.wrong, { max: 5000 })
+      };
+    });
+
+    return sanitized;
+  }
+
+  _sanitizeLessonState(value) {
+    if (!value || typeof value !== 'object' || Array.isArray(value)) {
+      return {};
+    }
+
+    const knownKeys = [
+      'version',
+      'updatedAt',
+      'activeTab',
+      'exercisePreparationCompleted',
+      'lessonPrepStage',
+      'lessonPrepIndex',
+      'vocabTrainerActive',
+      'vocabTrainerMode',
+      'vocabTrainerAutoSwitchedToTyping',
+      'vocabTrainerCorrect',
+      'vocabTrainerWrong',
+      'vocabTrainerTotalAttempts',
+      'vocabTrainerCurrentAttempts',
+      'vocabTrainerReviewAttempts',
+      'vocabTrainerStats',
+      'exerciseAnswers',
+      'exerciseResults',
+      'exerciseRetryPending',
+      'exerciseRetryPendingSinceAttempts'
+    ];
+    const hasKnownState = knownKeys.some((key) => Object.prototype.hasOwnProperty.call(value, key));
+    if (!hasKnownState) {
+      return {};
+    }
+
+    const activeTab = value.activeTab === 'exercises' ? 'exercises' : 'learn';
+    const vocabTrainerMode = value.vocabTrainerMode === 'typing' ? 'typing' : 'multiple_choice';
+
+    return {
+      version: this._clampInteger(value.version, { min: 1, max: 1000, fallback: 1 }),
+      updatedAt: this._sanitizeShortString(value.updatedAt || new Date().toISOString(), 64),
+      activeTab,
+      exercisePreparationCompleted: Boolean(value.exercisePreparationCompleted),
+      lessonPrepStage: this._clampInteger(value.lessonPrepStage, { min: 0, max: 2 }),
+      lessonPrepIndex: this._clampInteger(value.lessonPrepIndex, { min: 0, max: 500 }),
+      vocabTrainerActive: Boolean(value.vocabTrainerActive),
+      vocabTrainerMode,
+      vocabTrainerAutoSwitchedToTyping: Boolean(value.vocabTrainerAutoSwitchedToTyping),
+      vocabTrainerCorrect: this._clampInteger(value.vocabTrainerCorrect, { max: 5000 }),
+      vocabTrainerWrong: this._clampInteger(value.vocabTrainerWrong, { max: 5000 }),
+      vocabTrainerTotalAttempts: this._clampInteger(value.vocabTrainerTotalAttempts, { max: 10000 }),
+      vocabTrainerCurrentAttempts: this._clampInteger(value.vocabTrainerCurrentAttempts, { max: 10000 }),
+      vocabTrainerReviewAttempts: this._clampInteger(value.vocabTrainerReviewAttempts, { max: 10000 }),
+      vocabTrainerStats: this._sanitizeVocabTrainerStats(value.vocabTrainerStats),
+      exerciseAnswers: this._sanitizeExerciseAnswers(value.exerciseAnswers),
+      exerciseResults: this._sanitizeExerciseResults(value.exerciseResults),
+      exerciseRetryPending: Boolean(value.exerciseRetryPending),
+      exerciseRetryPendingSinceAttempts: this._clampInteger(value.exerciseRetryPendingSinceAttempts, { max: 10000 })
+    };
+  }
+
+  _serializeLessonProgress(progress, lessonData = null) {
+    if (!progress) {
+      return null;
+    }
+
+    const plainProgress = progress.get ? progress.get({ plain: true }) : { ...progress };
+    const targetScore = lessonData?.targetScorePercent || plainProgress.lesson?.targetScorePercent || 80;
+    const hasReachedTarget = (plainProgress.score || 0) >= targetScore;
+
+    return {
+      ...plainProgress,
+      lessonState: this._sanitizeLessonState(plainProgress.lessonState),
+      targetScore,
+      hasReachedTarget,
+      needsReview: Boolean((lessonData?.requiresReview ?? plainProgress.lesson?.requiresReview) && !hasReachedTarget)
+    };
+  }
+
   async _getUserByHashedId(hashedUserId) {
     const user = await User.findOne({ where: { hashedId: hashedUserId } });
     if (!user) {
@@ -1652,6 +1827,13 @@ export default class VocabService {
       throw err;
     }
 
+    const progress = await VocabCourseProgress.findOne({
+      where: {
+        userId: user.id,
+        lessonId: lesson.id
+      }
+    });
+
     const plainLesson = lesson.get({ plain: true });
     
     // Lade Vokabeln aus vorherigen Lektionen (für Wiederholung UND für gemischten Vokabeltrainer)
@@ -1666,6 +1848,7 @@ export default class VocabService {
     
     plainLesson.didactics = this._buildLessonDidactics(plainLesson);
     plainLesson.pedagogy = this._buildLessonPedagogy(plainLesson);
+    plainLesson.progress = this._serializeLessonProgress(progress, plainLesson);
     return plainLesson;
   }
 
@@ -2053,10 +2236,10 @@ export default class VocabService {
       order: [[{ model: VocabCourseLesson, as: 'lesson' }, 'lessonNumber', 'ASC']]
     });
 
-    return progress.map(p => p.get({ plain: true }));
+    return progress.map((entry) => this._serializeLessonProgress(entry, entry.lesson));
   }
 
-  async updateLessonProgress(hashedUserId, lessonId, { completed, score, timeSpentMinutes }) {
+  async updateLessonProgress(hashedUserId, lessonId, { completed, score, timeSpentMinutes, lessonState }) {
     const user = await this._getUserByHashedId(hashedUserId);
     const lesson = await VocabCourseLesson.findByPk(lessonId, {
       include: [{ model: VocabCourse, as: 'course' }]
@@ -2083,6 +2266,7 @@ export default class VocabService {
     const targetScore = lessonData.targetScorePercent || 80;
     const actualScore = Number(score) || 0;
     const hasReachedTarget = actualScore >= targetScore;
+    const sanitizedLessonState = lessonState === undefined ? undefined : this._sanitizeLessonState(lessonState);
     
     // Prüfe, ob Lektion als abgeschlossen gilt (nur wenn Ziel erreicht oder explizit completed=true)
     const isCompleted = Boolean(completed) || (hasReachedTarget && lessonData.requiresReview === false);
@@ -2095,6 +2279,7 @@ export default class VocabService {
         lessonId: lesson.id,
         completed: isCompleted,
         score: actualScore,
+        lessonState: sanitizedLessonState || {},
         lastAccessedAt: new Date()
       }
     });
@@ -2117,6 +2302,9 @@ export default class VocabService {
           updates.completedAt = new Date();
         }
       }
+      if (sanitizedLessonState !== undefined) {
+        updates.lessonState = sanitizedLessonState;
+      }
       await progress.update(updates);
     } else if (isCompleted) {
       progress.completed = true;
@@ -2124,12 +2312,7 @@ export default class VocabService {
       await progress.save();
     }
 
-    const progressData = progress.get({ plain: true });
-    progressData.targetScore = targetScore;
-    progressData.hasReachedTarget = progressData.score >= targetScore;
-    progressData.needsReview = lessonData.requiresReview && !progressData.hasReachedTarget;
-
-    return progressData;
+    return this._serializeLessonProgress(progress, lessonData);
   }
 
   // ========== GRAMMAR EXERCISE METHODS ==========