package com.ybw.mathapp.service;

import java.util.*;

/**
 * 扩展的计算类，支持基础四则运算、括号、平方、开根号、三角函数 (sin, cos, tan)。
 * 括号优先级最高。
 * 高级运算符 (平方, 开根号, sin, cos, tan) 优先级高于四则运算。
 * 平方是后置运算符，开根号和三角函数是前置运算符。
 * 例如: "3 + 开根号 16 平方" 解释为 "3 + (sqrt(16))^2" = "3 + 4^2" = "3 + 16" = 19
 *       "开根号 ( 4 + 5 ) 平方" 解释为 "(sqrt(4+5))^2" = "sqrt(9)^2" = "3^2" = 9
 *       "sin 30 + 5" 解释为 "sin(30) + 5" (假设30是度数)
 * 修正：在计算开根号时，若操作数为负数，则抛出 ArithmeticException。
 */
public class AdvancedCaculate {

  private static final Set<String> OPERATORS = new HashSet<>(Arrays.asList("+", "-", "*", "/"));
  private static final Set<String> ADVANCED_OPERATORS = new HashSet<>(Arrays.asList("平方", "开根号", "sin", "cos", "tan"));
  private static final Map<String, Integer> PRECEDENCE = new HashMap<>();

  static {
    PRECEDENCE.put("+", 1);
    PRECEDENCE.put("-", 1);
    PRECEDENCE.put("*", 2);
    PRECEDENCE.put("/", 2);
    // 高级运算符优先级更高
    PRECEDENCE.put("平方", 3); // 后置
    PRECEDENCE.put("开根号", 3); // 前置
    PRECEDENCE.put("sin", 3);   // 前置
    PRECEDENCE.put("cos", 3);   // 前置
    PRECEDENCE.put("tan", 3);   // 前置
  }

  /**
   * 计算给定表达式的值。
   *
   * @param expressionTokens 表达式分词列表，例如 ["3", "+", "开根号", "16", "平方"]
   * @return 计算结果
   * @throws IllegalArgumentException 如果表达式无效
   * @throws ArithmeticException        如果计算过程中出现错误（如除零、负数开根号）
   */
  public static double calculate(List<String> expressionTokens) {
    Stack<Double> numberStack = new Stack<>();
    Stack<String> operatorStack = new Stack<>();

    for (int i = 0; i < expressionTokens.size(); i++) {
      String token = expressionTokens.get(i);

      if (isNumeric(token)) {
        numberStack.push(Double.parseDouble(token));
      } else if (token.equals("(")) {
        operatorStack.push(token);
      } else if (token.equals(")")) {
        while (!operatorStack.isEmpty() && !operatorStack.peek().equals("(")) {
          processOperator(numberStack, operatorStack.pop());
        }
        if (!operatorStack.isEmpty()) { // Pop the "("
          operatorStack.pop();
        }
      } else if (ADVANCED_OPERATORS.contains(token)) {
        // 前置运算符 (开根号, sin, cos, tan) 直接入栈
        // 后置运算符 (平方) 需要等待其操作数先计算出来
        // 在标准调度场算法中，后置运算符通常在遇到时立即处理其栈顶的操作数
        // 这里我们可以在遇到 "平方" 时，立即对 numberStack 的顶部元素进行平方操作
        if ("平方".equals(token)) {
          if (numberStack.isEmpty()) {
            throw new IllegalArgumentException("Invalid expression: '平方' lacks an operand.");
          }
          double operand = numberStack.pop();
          numberStack.push(Math.pow(operand, 2));
        } else { // "开根号", "sin", "cos", "tan" 是前置运算符
          operatorStack.push(token);
        }
      } else if (OPERATORS.contains(token)) {
        // 处理四则运算符，遵循优先级
        while (!operatorStack.isEmpty() &&
            !operatorStack.peek().equals("(") &&
            PRECEDENCE.get(token) <= PRECEDENCE.getOrDefault(operatorStack.peek(), 0)) {
          processOperator(numberStack, operatorStack.pop());
        }
        operatorStack.push(token);
      } else {
        throw new IllegalArgumentException("Unknown token: " + token);
      }
    }

    // 处理栈中剩余的所有运算符
    while (!operatorStack.isEmpty()) {
      String op = operatorStack.pop();
      if (op.equals("(") || op.equals(")")) {
        throw new IllegalArgumentException("Mismatched parentheses in expression.");
      }
      processOperator(numberStack, op);
    }

    if (numberStack.size() != 1 || !operatorStack.isEmpty()) {
      throw new IllegalArgumentException("Invalid expression: " + String.join(" ", expressionTokens));
    }

    return numberStack.pop();
  }

  /**
   * 执行一次运算操作。
   *
   * @param numberStack 数字栈
   * @param operator    运算符
   */
  private static void processOperator(Stack<Double> numberStack, String operator) {
    if (numberStack.size() < 1) {
      throw new IllegalArgumentException("Invalid expression: operator '" + operator + "' lacks operand(s).");
    }

    if (ADVANCED_OPERATORS.contains(operator)) {
      double operand = numberStack.pop();
      switch (operator) {
        case "开根号":
          if (operand < 0) {
            // 抛出异常，让调用者（MultipleChoiceGenerator）处理
            throw new ArithmeticException("Cannot take square root of negative number: " + operand);
          }
          numberStack.push(Math.sqrt(operand));
          break;
        case "sin":
          numberStack.push(Math.sin(Math.toRadians(operand))); // 假设输入是度数
          break;
        case "cos":
          numberStack.push(Math.cos(Math.toRadians(operand)));
          break;
        case "tan":
          // tan(90 + n*180) 会趋向无穷，这里不特别处理，让其返回 Infinity 或 -Infinity
          numberStack.push(Math.tan(Math.toRadians(operand)));
          break;
        default:
          throw new IllegalArgumentException("Unknown advanced operator: " + operator);
      }
    } else if (OPERATORS.contains(operator)) {
      if (numberStack.size() < 2) {
        throw new IllegalArgumentException("Invalid expression: operator '" + operator + "' lacks operand(s).");
      }
      double b = numberStack.pop();
      double a = numberStack.pop();
      double result;
      switch (operator) {
        case "+":
          result = a + b;
          break;
        case "-":
          result = a - b;
          break;
        case "*":
          result = a * b;
          break;
        case "/":
          if (b == 0) {
            throw new ArithmeticException("Division by zero");
          }
          result = a / b;
          break;
        default:
          throw new IllegalArgumentException("Unknown operator: " + operator);
      }
      numberStack.push(result);
    } else {
      throw new IllegalArgumentException("Unexpected operator in process: " + operator);
    }
  }

  public static boolean isNumeric(String str) {
    if (str == null || str.isEmpty()) {
      return false;
    }
    try {
      Double.parseDouble(str);
      return true;
    } catch (NumberFormatException e) {
      return false;
    }
  }
}