add backend

backend/src/main/java/com/yoyuzh/auth/AuthService.java

@@ -0,0 +1,83 @@
+package com.yoyuzh.auth;
+
+import com.yoyuzh.auth.dto.AuthResponse;
+import com.yoyuzh.auth.dto.LoginRequest;
+import com.yoyuzh.auth.dto.RegisterRequest;
+import com.yoyuzh.auth.dto.UserProfileResponse;
+import com.yoyuzh.common.BusinessException;
+import com.yoyuzh.common.ErrorCode;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@RequiredArgsConstructor
+public class AuthService {
+
+    private final UserRepository userRepository;
+    private final PasswordEncoder passwordEncoder;
+    private final AuthenticationManager authenticationManager;
+    private final JwtTokenProvider jwtTokenProvider;
+
+    @Transactional
+    public AuthResponse register(RegisterRequest request) {
+        if (userRepository.existsByUsername(request.username())) {
+            throw new BusinessException(ErrorCode.UNKNOWN, "用户名已存在");
+        }
+        if (userRepository.existsByEmail(request.email())) {
+            throw new BusinessException(ErrorCode.UNKNOWN, "邮箱已存在");
+        }
+
+        User user = new User();
+        user.setUsername(request.username());
+        user.setEmail(request.email());
+        user.setPasswordHash(passwordEncoder.encode(request.password()));
+        User saved = userRepository.save(user);
+        return new AuthResponse(jwtTokenProvider.generateToken(saved.getId(), saved.getUsername()), toProfile(saved));
+    }
+
+    public AuthResponse login(LoginRequest request) {
+        try {
+            authenticationManager.authenticate(
+                    new UsernamePasswordAuthenticationToken(request.username(), request.password()));
+        } catch (BadCredentialsException ex) {
+            throw new BusinessException(ErrorCode.NOT_LOGGED_IN, "用户名或密码错误");
+        }
+
+        User user = userRepository.findByUsername(request.username())
+                .orElseThrow(() -> new BusinessException(ErrorCode.NOT_LOGGED_IN, "用户不存在"));
+        return new AuthResponse(jwtTokenProvider.generateToken(user.getId(), user.getUsername()), toProfile(user));
+    }
+
+    @Transactional
+    public AuthResponse devLogin(String username) {
+        String candidate = username == null ? "" : username.trim();
+        if (candidate.isEmpty()) {
+            candidate = "1";
+        }
+
+        final String finalCandidate = candidate;
+        User user = userRepository.findByUsername(finalCandidate).orElseGet(() -> {
+            User created = new User();
+            created.setUsername(finalCandidate);
+            created.setEmail(finalCandidate + "@dev.local");
+            created.setPasswordHash(passwordEncoder.encode("1"));
+            return userRepository.save(created);
+        });
+        return new AuthResponse(jwtTokenProvider.generateToken(user.getId(), user.getUsername()), toProfile(user));
+    }
+
+    public UserProfileResponse getProfile(String username) {
+        User user = userRepository.findByUsername(username)
+                .orElseThrow(() -> new BusinessException(ErrorCode.NOT_LOGGED_IN, "用户不存在"));
+        return toProfile(user);
+    }
+
+    private UserProfileResponse toProfile(User user) {
+        return new UserProfileResponse(user.getId(), user.getUsername(), user.getEmail(), user.getCreatedAt());
+    }
+}