public class PrimaryQuestionGenerator extends AbstractQuestionGenerator {
    private static final String[] OPERATORS = {"+", "-", "×", "÷"};
    
    @Override
    public String generateQuestion() {
        int attempts = 0;
        while (attempts < 100) {
            attempts++; 
            int operandCount = random.nextInt(4) + 2; // 2~5个操作数
            StringBuilder question = new StringBuilder();
            
            // 生成操作数和运算符
            for (int i = 0; i < operandCount; i++) {
                question.append(generateNumber());
                if (i < operandCount - 1) {
                    question.append(" ").append(generateOperator(OPERATORS)).append(" ");
                }
            }
            // 随机添加括号
            String result = addReasonableParentheses(question.toString(), operandCount);
            result = ensureBalancedParentheses(result); // 确保括号平衡
            
            if (isQuestionUnique(result) && isValidParentheses(result) && hasOperator(result)) {
                addToGeneratedQuestions(result);
                String regex = "(?<!\\s)\\)(?=[^)]*$)";
                result = result.replaceAll(regex, " )");
                return result;
            }
        }
        return "3 + 5"; // 备用题目
    }
    
    private String addReasonableParentheses(String expression, int operandCount) {
    	if (operandCount <= 2 || random.nextDouble() < 0.3) {
            return expression;
        }
        
        String[] parts = expression.split(" ");
        if (parts.length < 5) return expression;
        
        StringBuilder newExpr = new StringBuilder();
        
        int start = random.nextInt(parts.length / 2);
        int end = start + random.nextInt(parts.length / 2 - start + 1) + 1;
        end = Math.min(end, parts.length / 2 - 1);
        
        for (int i = 0; i < parts.length; i++) {
            if (i == start * 2) {
                newExpr.append("( ");
            }
            newExpr.append(parts[i]);
            
            if (i == end * 2 && i >= start * 2 + 2) {
                newExpr.append(" )");
            }
            if (i < parts.length - 1) {
                newExpr.append(" ");
            }
        }
        
        return newExpr.toString().trim();
    }
    
}