package mathpuzzle.service;

import static mathpuzzle.service.PrimarySchoolGenerator.isNumeric;

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

/**
 * 高中题目生成器 题目必须包含至少一个 sin, cos, tan 三角函数运算符
 */
public class SeniorHighGenerator implements QuestionGenerator {

  private static final String[] TRIG_FUNCS = {"sin", "cos", "tan"};
  private static final String[] OPERATORS = {"+", "-", "*", "/"};
  private final Random random = new Random();

  @Override
  public List<String> generateQuestions(int count) {
    List<String> questions = new ArrayList<>();
    for (int i = 0; i < count; i++) {
      String question = generateSingleQuestion();
      questions.add(question);
    }
    return questions;
  }

  private String generateSingleQuestion() {
    List<String> parts = new ArrayList<>();
    int operandCount = random.nextInt(5) + 1;
    parts = generateBase(operandCount, parts);
    String advancedOp;
    // hasAdvancedOp用以检测下面的循环是否加入了高级运算符，如果没有就启动保底
    if (operandCount == 1) {
      advancedOp = TRIG_FUNCS[random.nextInt(TRIG_FUNCS.length)];
      parts.set(0, advancedOp + parts.get(0));
    } else {
      // 遍历查找左括号的合理位置
      for (int i = 0; i < parts.size(); i++) {
        // 最后一次循环保底生成高中三角函数
        if (i == parts.size() - 1) {
          advancedOp = TRIG_FUNCS[random.nextInt(TRIG_FUNCS.length)];
          parts.set(i, advancedOp + parts.get(i));
        } else if (isNumeric(parts.get(i)) && random.nextBoolean()) {// 随机数看是否为操作数且随即进入生成程序
          // 进入随机生成tan\sin\cos的程序
          parts = generateTrig(parts, i);
          break;
        }
      }
    }
    return String.join(" ", parts) + " =";
  }

  // 产生基本操作
  public List<String> generateBase(int operandCount, List<String> parts) {
    for (int i = 0; i < operandCount; i++) {
      int num = random.nextInt(100) + 1;
      parts.add(String.valueOf(num));
      if (i < operandCount - 1) {
        parts.add(OPERATORS[random.nextInt(OPERATORS.length)]);
      }
    }
    return parts;
  }

  // 产生三角函数运算符
  public List<String> generateTrig(List<String> parts, int i) {
    String trigOp = TRIG_FUNCS[random.nextInt(TRIG_FUNCS.length)];
    if (random.nextBoolean()) {
      parts.set(i, trigOp + parts.get(i));
    } else {
      parts.set(i, trigOp + "(" + parts.get(i));
      // 为避免随机数上限出现0，此处要单独判断一下左括号正好括住倒数第二个操作数的情况
      if (i == parts.size() - 3) {
        parts.set(parts.size() - 1, parts.get(parts.size() - 1) + ")");
      } else {
        while (true) {
          int i2 = random.nextInt(parts.size() - 3 - i) + 2;
          if (isNumeric(parts.get(i + i2))) {
            parts.set(i + i2, parts.get(i + i2) + ")");
            break;
          }
        }
      }
    }
    return parts;
  }
}