MathLearningSoftware/src/com/mathlearning/model/BaseQuestionGenerator.java

package com.mathlearning.model;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
import java.util.Set;

public abstract class BaseQuestionGenerator {
  protected Random random = new Random();

  public abstract Question generateQuestion(int index);

  protected void generateOperands(int[] operands, int min, int max) {
    for (int i = 0; i < operands.length; i++) {
      operands[i] = random.nextInt(max - min + 1) + min;
    }
  }

  protected void generateOperations(int[] operations, int operationTypes) {
    for (int i = 0; i < operations.length; i++) {
      operations[i] = random.nextInt(operationTypes);
    }
  }

  protected void appendOperator(StringBuilder sb, int operation) {
    switch (operation) {
      case 0:
        sb.append(" + ");
        break;
      case 1:
        sb.append(" - ");
        break;
      case 2:
        sb.append(" × ");
        break;
      case 3:
        sb.append(" ÷ ");
        break;
    }
  }

  protected boolean isValidAnswer(double answer) {
    return !(answer < 0 || Double.isNaN(answer) || Double.isInfinite(answer));
  }

  protected double calculateExpression(double[] values, int[] operations) {
    List<Double> numbers = new ArrayList<>();
    List<Integer> ops = new ArrayList<>();

    for (double value : values) numbers.add(value);
    for (int operation : operations) ops.add(operation);

    processMultiplicationAndDivision(numbers, ops);
    return processAdditionAndSubtraction(numbers, ops);
  }

  protected double calculateWithoutParentheses(int[] operands, int[] operations) {
    double[] doubleOperands = new double[operands.length];
    for (int i = 0; i < operands.length; i++) {
      doubleOperands[i] = operands[i];
    }
    return calculateExpression(doubleOperands, operations);
  }

  protected double calculateWithoutParentheses(List<Integer> numbers, List<Integer> ops) {
    double[] doubleNumbers = new double[numbers.size()];
    for (int i = 0; i < numbers.size(); i++) {
      doubleNumbers[i] = numbers.get(i);
    }

    int[] intOps = new int[ops.size()];
    for (int i = 0; i < ops.size(); i++) {
      intOps[i] = ops.get(i);
    }

    return calculateExpression(doubleNumbers, intOps);
  }

  private void processMultiplicationAndDivision(List<Double> numbers, List<Integer> ops) {
    for (int i = 0; i < ops.size(); i++) {
      int op = ops.get(i);
      if (op == 2 || op == 3) {
        double left = numbers.get(i);
        double right = numbers.get(i + 1);
        double result = performOperation(left, right, op);

        numbers.set(i, result);
        numbers.remove(i + 1);
        ops.remove(i);
        i--;
      }
    }
  }

  private double processAdditionAndSubtraction(List<Double> numbers, List<Integer> ops) {
    double result = numbers.get(0);

    for (int i = 0; i < ops.size(); i++) {
      int op = ops.get(i);
      double nextNum = numbers.get(i + 1);
      result = performOperation(result, nextNum, op);
    }

    return Math.round(result * 100) / 100.0;
  }

  private double performOperation(double left, double right, int operation) {
    switch (operation) {
      case 0:
        return left + right;
      case 1:
        return left - right;
      case 2:
        return left * right;
      case 3:
        if (right == 0) return Double.NaN;
        return left / right;
      default:
        return left;
    }
  }

  protected Question generateOptions(String questionText, double answer, String level) {
    String[] options = new String[4];
    Set<String> usedValues = new HashSet<>();

    boolean isIntegerAnswer = (answer == (int) answer);
    String correctAnswer = formatAnswer(answer);

    options[0] = correctAnswer;
    usedValues.add(correctAnswer);

    generateWrongOptions(options, usedValues, answer, isIntegerAnswer);
    shuffleArray(options);

    int correctIndex = findCorrectIndex(options, correctAnswer);
    return new Question(questionText, options, correctIndex, level);
  }

  private void generateWrongOptions(
      String[] options, Set<String> usedValues, double answer, boolean isIntegerAnswer) {
    for (int i = 1; i < 4; i++) {
      String wrongAnswer;
      int attempts = 0;

      do {
        double wrongValue = generateWrongValue(answer, isIntegerAnswer);
        wrongAnswer = formatAnswer(wrongValue);
        attempts++;
      } while (usedValues.contains(wrongAnswer) && attempts < 20);

      options[i] = wrongAnswer;
      usedValues.add(wrongAnswer);
    }
  }

  private double generateWrongValue(double answer, boolean isIntegerAnswer) {
    double offset = (random.nextDouble() * 5) + 1;

    if (isIntegerAnswer) {
      int intAnswer = (int) answer;
      int intOffset = random.nextInt(10) + 1;
      double wrongValue =
          random.nextBoolean() ? intAnswer + intOffset : Math.max(1, intAnswer - intOffset);
      return (int) wrongValue;
    } else {
      double wrongValue = random.nextBoolean() ? answer + offset : answer - offset;
      return Math.round(wrongValue * 100) / 100.0;
    }
  }

  private String formatAnswer(double answer) {
    return (answer == (int) answer) ? String.valueOf((int) answer) : String.format("%.2f", answer);
  }

  private void shuffleArray(String[] array) {
    for (int i = array.length - 1; i > 0; i--) {
      int j = random.nextInt(i + 1);
      String temp = array[i];
      array[i] = array[j];
      array[j] = temp;
    }
  }

  private int findCorrectIndex(String[] options, String correctAnswer) {
    for (int i = 0; i < options.length; i++) {
      if (options[i].equals(correctAnswer)) return i;
    }
    return 0;
  }
}