feat(auth+db): 实现注册登录核心逻辑，以及自动建表，用户信息落库

backend/internal/service/auth.go

@@ -0,0 +1,79 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"gen2d/internal/db"
+	"gen2d/internal/model"
+
+	"github.com/golang-jwt/jwt/v5"
+	"golang.org/x/crypto/bcrypt"
+	"gorm.io/gorm"
+)
+
+// AuthService 用户认证服务。
+type AuthService struct {
+	jwtSecret []byte
+	jwtExpire time.Duration
+}
+
+// NewAuthService 创建 AuthService 实例。
+func NewAuthService(jwtSecret string, jwtExpire int64) *AuthService {
+	return &AuthService{
+		jwtSecret: []byte(jwtSecret),
+		jwtExpire: time.Duration(jwtExpire) * time.Second,
+	}
+}
+
+// Register 注册新用户，密码使用 bcrypt 加密存储。
+func (s *AuthService) Register(ctx context.Context, username, password, email string) (*model.User, error) {
+	hashed, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		return nil, err
+	}
+
+	user := model.User{
+		Username: username,
+		Password: string(hashed),
+		Email:    email,
+	}
+
+	if err := db.DB.WithContext(ctx).Create(&user).Error; err != nil {
+		if errors.Is(err, gorm.ErrDuplicatedKey) {
+			return nil, errors.New("用户名已存在")
+		}
+		return nil, err
+	}
+
+	return &user, nil
+}
+
+// Login 校验用户名密码，成功返回 JWT token 及用户信息。
+func (s *AuthService) Login(ctx context.Context, username, password string) (string, int64, *model.User, error) {
+	var user model.User
+	if err := db.DB.WithContext(ctx).Where("username = ?", username).First(&user).Error; err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return "", 0, nil, errors.New("用户名或密码错误")
+		}
+		return "", 0, nil, err
+	}
+
+	if err := bcrypt.CompareHashAndPassword([]byte(user.Password), []byte(password)); err != nil {
+		return "", 0, nil, errors.New("用户名或密码错误")
+	}
+
+	expiresAt := time.Now().Add(s.jwtExpire)
+	claims := jwt.MapClaims{
+		"sub": user.ID,
+		"exp": expiresAt.Unix(),
+		"iat": time.Now().Unix(),
+	}
+	token, err := jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString(s.jwtSecret)
+	if err != nil {
+		return "", 0, nil, err
+	}
+
+	return token, int64(s.jwtExpire.Seconds()), &user, nil
+}