import java.util.ArrayList;
import java.util.List;

/**
 * 高中题目生成器（具体策略）。
 * 它首先生成一个包含初中难度运算（平方/开方）的题目，
 * 然后再额外加入一个三角函数运算，使得题目难度递增。
 */
public class HighSchoolProblemGenerator extends MiddleSchoolProblemGenerator {

  private static final int[] PREDEFINED_ANGLES = {0, 30, 45, 60, 90};
  private static final String[] TRIG_FUNCTIONS = {"sin", "cos", "tan"};

  @Override
  protected Equation createProblem() {
    // 1. 调用父类（已修正的 MiddleSchoolProblemGenerator）的方法
    Equation middleSchoolEquation = super.createProblem();

    List<String> operands = new ArrayList<>(middleSchoolEquation.getOperands());
    List<Operator> operators = new ArrayList<>(middleSchoolEquation.getOperators());

    // 2. 随机替换一个操作数为三角函数
    int modifyIndex = random.nextInt(operands.size());
    int angle = PREDEFINED_ANGLES[random.nextInt(PREDEFINED_ANGLES.length)];
    String funcType = TRIG_FUNCTIONS[random.nextInt(TRIG_FUNCTIONS.length)];

    if ("tan".equals(funcType) && angle == 90) {
      angle = 45; // 避免 tan(90)
    }

    String trigExpression = String.format("%s(%d)", funcType, angle);
    operands.set(modifyIndex, trigExpression);

    return new Equation(operands, operators);
  }
}