package question;

import java.util.Random;

public class PrimaryQuestionGenerator implements QuestionGenerator {
    private static final Random random = new Random();

    @Override
    public Question generateQuestion() {
        int numOperands = random.nextInt(5) + 1;
        StringBuilder sb = new StringBuilder();
        int currentValue = random.nextInt(100) + 1;
        sb.append(currentValue);

        for (int i = 1; i < numOperands; i++) {
            String[] ops = {"+", "-", "*", "/"};
            String op;
            int nextVal;
            do {
                op = ops[random.nextInt(ops.length)];
                nextVal = random.nextInt(100) + 1;
            } while ((op.equals("-") && currentValue < nextVal) ||
                    (op.equals("/") && (nextVal == 0 || currentValue % nextVal != 0)));

            sb.append(" ").append(op).append(" ").append(nextVal);
            switch (op) {
                case "+": currentValue += nextVal; break;
                case "-": currentValue -= nextVal; break;
                case "*": currentValue *= nextVal; break;
                case "/": currentValue /= nextVal; break;
            }
        }

        String expr = addParentheses(sb.toString());
        return new Question(expr, evaluate(expr));
    }

    private String addParentheses(String expr) {
        String[] tokens = expr.split(" ");
        if (tokens.length < 3) return expr;

        int start = random.nextInt(tokens.length / 2) * 2;
        int end = start + 2 + random.nextInt((tokens.length - start) / 2) * 2;
        end = Math.min(end, tokens.length - 1);

        StringBuilder newExpr = new StringBuilder();
        for (int i = 0; i < tokens.length; i++) {
            if (i == start) newExpr.append("(");
            newExpr.append(tokens[i]);
            if (i == end) newExpr.append(")");
            if (i != tokens.length - 1) newExpr.append(" ");
        }
        return newExpr.toString();
    }

    private String evaluate(String expr) {
        try {
            javax.script.ScriptEngineManager mgr = new javax.script.ScriptEngineManager();
            javax.script.ScriptEngine engine = mgr.getEngineByName("JavaScript");
            return String.valueOf(engine.eval(expr));
        } catch (Exception e) {
            return "?";
        }
    }
}