删除InvalidInputException和所有相关用法

删除EducationLevel和所有相关用法，为简化逻辑，改为直接使用难度字符串

src/Application.java

@@ -108,11 +108,10 @@ public class Application {
   private void handleSwitchLevel(String input) {
     Matcher matcher = SWITCH_COMMAND_PATTERN.matcher(input);
     if (matcher.matches()) {
-      String levelName = matcher.group(1);
-      EducationLevel level = EducationLevel.fromLevelName(levelName);
+      String level = matcher.group(1);
       if (level != null) {
         sessionManager.setCurrentGenerator(level);
-        System.out.println("成功切换到 " + levelName + " 出题模式。");
+        System.out.println("成功切换到 " + level + " 出题模式。");
       }
     }
   }

src/EducationLevel.java

@@ -1,39 +0,0 @@
-/**
- * 教育级别枚举。
- * 用于表示用户的默认级别以及题目生成的难度。
- */
-public enum EducationLevel {
-  PRIMARY("小学"),
-  MIDDLE("初中"),
-  HIGH("高中");
-
-  private final String levelName;
-
-  EducationLevel(String levelName) {
-    this.levelName = levelName;
-  }
-
-  /**
-   * 获取级别的名称。
-   *
-   * @return 级别名称字符串
-   */
-  public String getLevelName() {
-    return levelName;
-  }
-
-  /**
-   * 根据中称查找对应的枚举实例。
-   *
-   * @param levelName 要查找的名称，例如 "初中"
-   * @return 匹配的 EducationLevel 实例，若未找到则返回 null
-   */
-  public static EducationLevel fromLevelName(String levelName) {
-    for (EducationLevel level : values()) {
-      if (level.getLevelName().equals(levelName)) {
-        return level;
-      }
-    }
-    return null;
-  }
-}

src/InMemoryUserRepository.java

@@ -13,17 +13,17 @@ public class InMemoryUserRepository implements UserRepository {
   public InMemoryUserRepository() {
     // 初始化预定义的9个用户账户
     // 小学老师
-    userDatabase.put("张三1", new User("张三1", "123", EducationLevel.PRIMARY));
-    userDatabase.put("张三2", new User("张三2", "123", EducationLevel.PRIMARY));
-    userDatabase.put("张三3", new User("张三3", "123", EducationLevel.PRIMARY));
+    userDatabase.put("张三1", new User("张三1", "123", "小学"));
+    userDatabase.put("张三2", new User("张三2", "123", "小学"));
+    userDatabase.put("张三3", new User("张三3", "123", "小学"));
     // 初中老师
-    userDatabase.put("李四1", new User("李四1", "123", EducationLevel.MIDDLE));
-    userDatabase.put("李四2", new User("李四2", "123", EducationLevel.MIDDLE));
-    userDatabase.put("李四3", new User("李四3", "123", EducationLevel.MIDDLE));
+    userDatabase.put("李四1", new User("李四1", "123", "初中"));
+    userDatabase.put("李四2", new User("李四2", "123", "初中"));
+    userDatabase.put("李四3", new User("李四3", "123", "初中"));
     // 高中老师
-    userDatabase.put("王五1", new User("王五1", "123", EducationLevel.HIGH));
-    userDatabase.put("王五2", new User("王五2", "123", EducationLevel.HIGH));
-    userDatabase.put("王五3", new User("王五3", "123", EducationLevel.HIGH));
+    userDatabase.put("王五1", new User("王五1", "123", "高中"));
+    userDatabase.put("王五2", new User("王五2", "123", "高中"));
+    userDatabase.put("王五3", new User("王五3", "123", "高中"));
   }
 
   @Override

src/SessionManager.java

@@ -38,7 +38,7 @@ public final class SessionManager {
   public void startSession(User user) {
     this.currentUser = user;
     // 根据用户的默认级别，初始化对应的题目生成策略
-    setGeneratorByDefaultLevel(user.getDefaultLevel());
+    setGeneratorByLevel(user.getDefaultLevel());
   }
 
   /**
@@ -66,27 +66,26 @@ public final class SessionManager {
    *
    * @param level 新的教育级别
    */
-  public void setCurrentGenerator(EducationLevel level) {
+  public void setCurrentGenerator(String level) {
     if (level == null) {
       throw new IllegalArgumentException("难度等级不可为空。");
     }
-    setGeneratorByDefaultLevel(level);
+    setGeneratorByLevel(level);
   }
 
-  private void setGeneratorByDefaultLevel(EducationLevel level) {
+  private void setGeneratorByLevel(String level) {
     switch (level) {
-      case PRIMARY:
+      case "小学":
         this.currentGenerator = new ElementaryProblemGenerator();
         break;
-      case MIDDLE:
+      case "初中":
         this.currentGenerator = new MiddleSchoolProblemGenerator();
         break;
-      case HIGH:
+      case "高中":
         this.currentGenerator = new HighSchoolProblemGenerator();
         break;
       default:
-        // 理论上不会发生，因为枚举是固定的
-        throw new IllegalStateException("错误的难度等级: " + level);
+        System.out.println("错误的难度等级: " + level);
     }
   }
 

src/User.java

@@ -8,10 +8,10 @@ public class User {
 
   private final String username;
   private final String password; // 注意：在生产系统中应存储哈希值
-  private final EducationLevel defaultLevel;
+  private final String defaultLevel;
   private final String storagePath;
 
-  public User(String username, String password, EducationLevel defaultLevel) {
+  public User(String username, String password, String defaultLevel) {
     this.username = username;
     this.password = password;
     this.defaultLevel = defaultLevel;
@@ -27,7 +27,7 @@ public class User {
     return password;
   }
 
-  public EducationLevel getDefaultLevel() {
+  public String getDefaultLevel() {
     return defaultLevel;
   }