feat(vocabService): enhance answer validation for multiple choice exercises

- Improved answer validation logic by expanding multiple choice answer data based on lesson context.
- Added methods to extract indices of correct answers and normalize question prompts for better accuracy.
- Refactored existing answer checking to accommodate new data handling, ensuring robust evaluation of user responses.

backend/services/vocabService.js

@@ -1702,8 +1702,18 @@ export default class VocabService {
       throw err;
     }
 
-    // Überprüfe Antwort (vereinfachte Logik - kann je nach Übungstyp erweitert werden)
-    const isCorrect = this._checkAnswer(exercise.answerData, exercise.questionData, userAnswer, exercise.exerciseTypeId);
+    const originalAnswerData = typeof exercise.answerData === 'string'
+      ? JSON.parse(exercise.answerData)
+      : exercise.answerData;
+    const questionData = typeof exercise.questionData === 'string'
+      ? JSON.parse(exercise.questionData)
+      : exercise.questionData;
+    const effectiveAnswerData = exercise.exerciseTypeId === 2
+      ? await this._expandMultipleChoiceAnswerData(exercise, originalAnswerData, questionData)
+      : originalAnswerData;
+
+    // Überprüfe Antwort
+    const isCorrect = this._checkAnswer(effectiveAnswerData, questionData, userAnswer, exercise.exerciseTypeId);
 
     // Speichere Fortschritt
     const [progress, created] = await VocabGrammarExerciseProgress.findOrCreate({
@@ -1736,12 +1746,7 @@ export default class VocabService {
     }
 
     // Extrahiere richtige Antwort und Alternativen
-    const answerData = typeof exercise.answerData === 'string' 
-      ? JSON.parse(exercise.answerData) 
-      : exercise.answerData;
-    const questionData = typeof exercise.questionData === 'string'
-      ? JSON.parse(exercise.questionData)
-      : exercise.questionData;
+    const answerData = effectiveAnswerData;
     
     let correctAnswer = null;
     let alternatives = [];
@@ -1817,6 +1822,86 @@ export default class VocabService {
     return type ? type.id : null;
   }
 
+  _extractMultipleChoiceIndices(answerData) {
+    if (!answerData) return [];
+    if (answerData.correctAnswer !== undefined) {
+      return Array.isArray(answerData.correctAnswer)
+        ? answerData.correctAnswer.map(idx => Number(idx)).filter(Number.isInteger)
+        : [Number(answerData.correctAnswer)].filter(Number.isInteger);
+    }
+    if (answerData.correct !== undefined) {
+      return Array.isArray(answerData.correct)
+        ? answerData.correct.map(idx => Number(idx)).filter(Number.isInteger)
+        : [Number(answerData.correct)].filter(Number.isInteger);
+    }
+    return [];
+  }
+
+  _getMultipleChoicePrompt(questionData) {
+    return this._normalizeTextAnswer(
+      questionData?.question || questionData?.text || questionData?.prompt || ''
+    );
+  }
+
+  async _expandMultipleChoiceAnswerData(exercise, answerData, questionData) {
+    const options = Array.isArray(questionData?.options) ? questionData.options : [];
+    const baseIndices = this._extractMultipleChoiceIndices(answerData);
+    if (!options.length || !baseIndices.length || !exercise?.lessonId) {
+      return answerData;
+    }
+
+    const prompt = this._getMultipleChoicePrompt(questionData);
+    if (!prompt) {
+      return answerData;
+    }
+
+    const optionIndexMap = new Map();
+    options.forEach((option, index) => {
+      const normalizedOption = this._normalizeTextAnswer(option);
+      if (!normalizedOption) return;
+      const existing = optionIndexMap.get(normalizedOption) || [];
+      existing.push(index);
+      optionIndexMap.set(normalizedOption, existing);
+    });
+
+    const lessonExercises = await VocabGrammarExercise.findAll({
+      where: {
+        lessonId: exercise.lessonId,
+        exerciseTypeId: 2
+      },
+      attributes: ['id', 'questionData', 'answerData']
+    });
+
+    const expandedIndices = new Set(baseIndices);
+    lessonExercises.forEach((candidate) => {
+      const candidateQuestionData = typeof candidate.questionData === 'string'
+        ? JSON.parse(candidate.questionData)
+        : candidate.questionData;
+      const candidatePrompt = this._getMultipleChoicePrompt(candidateQuestionData);
+      if (candidatePrompt !== prompt) {
+        return;
+      }
+
+      const candidateAnswerData = typeof candidate.answerData === 'string'
+        ? JSON.parse(candidate.answerData)
+        : candidate.answerData;
+      const candidateOptions = Array.isArray(candidateQuestionData?.options) ? candidateQuestionData.options : [];
+      const candidateIndices = this._extractMultipleChoiceIndices(candidateAnswerData);
+
+      candidateIndices.forEach((candidateIndex) => {
+        const candidateOption = candidateOptions[candidateIndex];
+        const normalizedOption = this._normalizeTextAnswer(candidateOption);
+        const matchingIndices = optionIndexMap.get(normalizedOption) || [];
+        matchingIndices.forEach((matchingIndex) => expandedIndices.add(matchingIndex));
+      });
+    });
+
+    return {
+      ...answerData,
+      correctAnswer: Array.from(expandedIndices).sort((a, b) => a - b)
+    };
+  }
+
   _checkAnswer(answerData, questionData, userAnswer, exerciseTypeId) {
     // Vereinfachte Antwortprüfung - kann je nach Übungstyp erweitert werden
     if (!answerData || userAnswer === undefined || userAnswer === null) return false;