BankQuestionSource.java

import java.util.List;
import java.util.Random;

/**
 * PART D: Question Sourcing Integration
 * Concrete QuestionSource - fetches pseudo-random predefined questions
 * from the QuestionBank repository.
 */
public class BankQuestionSource implements QuestionSource {

    private final Random random = new Random();
    private final List<Question> bank;
    private final String questionType;

    /**
     * @param questionType Filters bank items by type (e.g. "MCQ", "Essay").
     *                     Pass null to draw from the full bank.
     */
    public BankQuestionSource(String questionType) {
        this.questionType = questionType;
        this.bank = QuestionBank.getAll();
    }

    @Override
    public Question getQuestion() {
        List<Question> filtered = bank.stream()
                .filter(q -> questionType == null || q.getType().equalsIgnoreCase(questionType))
                .toList();

        if (filtered.isEmpty()) {
            throw new IllegalStateException(
                    "No questions of type '" + questionType + "' found in the bank.");
        }
        return filtered.get(random.nextInt(filtered.size()));
    }
}