// 第一个接口，创建一个帖子
@PostMapping("/threads")
public CommonResult<String> createThread(@RequestBody Thread thread) {...}

// 第二个接口，读取所有帖子
@GetMapping("/threads")
public CommonResult<List<Thread>> getThreads() {...}

// 第三个接口，读取指定 id 的帖子
@GetMapping("/threads/{id}")
public CommonResult<Thread> getThread(@PathVariable BigInteger id) {...}

// 第四个接口 (只写了 PUT)，更新一个帖子
@PutMapping("/threads/{id}")
public CommonResult<String> updateThread(@PathVariable BigInteger id, @RequestBody Thread thread) {...}

// 第五个接口，删除指定 id 的帖子
@DeleteMapping("/threads/{id}")
public CommonResult<String> deleteThread(@PathVariable BigInteger id) {...}

// 第六个接口，列出指定 id 的帖子的所有回复
@GetMapping("/threads/{threadId}/posts")
public CommonResult<List<Post>> getThreadPosts(@PathVariable BigInteger threadId) {...}

// 第七个接口，删除指定 id 的帖子下的指定 id 的回复
@DeleteMapping("/threads/{threadId}/posts/{postId}")
public CommonResult<String> deleteThreadPost(@PathVariable BigInteger threadId, @PathVariable BigInteger postId) {...}

public class User {
    private BigInteger id;
    private String userName;
    private String userPswHash;
    private String displayName;
    private int userLevel;
    private int userExp;
    // Getters and setters...
}

public interface UserMapper {
    @Select("SELECT * FROM user WHERE id = #{userId}")
    User findById(@Param("userId") String userId);
}

/********************
* 这样写其实不可取！！！！
********************/
@GetMapping("/users/{id}")
public User getUser(@PathVariable BigInteger id) {
    return userMapper.findById(id);
}

public class UserVO {
    private String displayName;
    private String userLevel;
    private String userExp;
    // Getters and Setters...
}

@GetMapping("/users/{id}")
public User getUser(@PathVariable BigInteger id) {
    // 先去数据库找 user
    User user = userMapper.findById(id);

    // 创建 userVO，把 user 中不敏感的数据拿出来，给到 userVO
    UserVO userVO = new userVO();
    userVO.setDisplayName(user.getDisplayName());
    userVO.setUserLevel(user.getUserLevel());
    userVO.setUserExp(user.getUserExp());

    // 把不包含敏感信息的 userVO 返回给用户
    return userVO;
}

@RestController
public class UserController {

    @Resource // 告诉 SpringBoot，如何初始化这个变量，这样就不用在 constructor 里去初始化了。
    private UserMapper userMapper;

    @GetMapping("/users/{id}")
    public CommonResult<UserVO> getUser(@PathVariable BigInteger id) {
        // 先去数据库找 user，跟之前一样，但是考虑数据库错误的情况
        User user;
        try {
            user = userMapper.findById(id);
        } catch (Exception e) {
            return CommonResult.failed("数据库错误。"); 
        }

        // 如果 user 找不到的话：
        if (!user) {
            return CommonResult.failed("操作失败，用户未找到。");
        }

        // 这跟之前一样
        UserVO userVO = new userVO();
        userVO.setDisplayName(user.getDisplayName());
        userVO.setUserLevel(user.getUserLevel());
        userVO.setUserExp(user.getUserExp());

        // 返回封装好的 result
        return CommonResult.success(userVO);
    }
}

@Service
public class UserService throws Exception{

    @Resource 
    private UserMapper userMapper;

    public User getUserById(BigInteger id) {
        User user;
        try {
            user = userMapper.findById(id);
        } catch (Exception e) {
            throw new Exception("Database error", e);
        }

        // 如果 user 找不到的话：
        if (user == null) {
            throw new NotFoundException("User not found");
        }
        
        return user;
    }

    public static UserVO UserToUserVO(User user) {
        UserVO userVO = new userVO();
        userVO.setDisplayName(user.getDisplayName());
        userVO.setUserLevel(user.getUserLevel());
        userVO.setUserExp(user.getUserExp());
        return userVO
    }
}

@RestController
public class UserController {

    // 用 UserService 去替换之前的 UserMapper
    // 这样 UserController 就没有权限去直接操控数据库了，一切处理都需要通过 UserService 完成
    @Resource
    private UserService userService; 

    @GetMapping("/users/{id}")
    public CommonResult<UserVO> getUser(@PathVariable BigInteger id) {
        // 先去数据库找 user，跟之前一样，但是考虑数据库错误的情况
        // 这跟之前一样
        try {
        	User user = userService.getUserById(id);
        } catch (NotFoundException e) {
            return CommonResult.failed(e.getMessage());
        } catch (Exception e) {
            e.printStackTrace(); // 这个错误信息对 debug 非常有用，要 print 出来
            return CommonResult.failed(e.getMessage());
        }
        UserVO userVO = UserService.UserToUserVO(user);
        // 返回封装好的 result
        return CommonResult.success(userVO);
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {

    // @ExceptionHandler 告诉 SpringBoot，所有的没有 catch 的 `NotFoundException` 全部送给这个函数处理
 	// @RespondBody 告诉 SpringBoot 把返回的对象变成 JSON（我们的 @RestController 标签其实就包含了 @ResponseBody)
    @ExceptionHandler(value=NotFoundException.class)
    @ResponseBody
    public CommonResult<String> notFoundExceptionHandler(NotFoundException e) {
        return CommonResult.failed(e.getMessage());
    }
    
    // 处理剩下的所有 Exception
    @ExceptionHandler(value = Exception.class)
    @ResponseBody
    public CommonResult<String> exceptionHandler(Exception e) {
        e.printStackTrace();
        return CommonResult.failed(e.getMessage());
    }

}

@GetMapping("/users/{id}")
public CommonResult<UserVO> getUser(@PathVariable BigInteger id) throws Exception {
    User user = userService.getUserById(id);
    UserVO userVO = UserService.UserToUserVO(user);
    return CommonResult.success(userVO);

public User getUserById(BigInteger id) {

    User user = userMapper.findById(id);
    if (user == null) {
        throw new NotFoundException("User not found");
    }
    return user;
}

@SpringBootApplication
@EnableSwagger2
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}