add login

internal/services/user/user_service.go

@@ -24,6 +24,12 @@ func (e *UsernameAlreadyExistsErr) Error() string {
 	return "username already exists error"
 }
 
+type UserNotFoundErr struct{}
+
+func (e *UserNotFoundErr) Error() string {
+	return "user not found error"
+}
+
 type UserService struct {
 	db *pgxpool.Pool
 }
@@ -54,6 +60,18 @@ func (s *UserService) AddUser(ctx context.Context, user *UserEntity) (*UserEntit
 	return user, nil
 }
 
+func (s *UserService) Login(ctx context.Context, user *UserEntity) (*UserEntity, error) {
+	query := `SELECT id FROM users WHERE username = @username AND password = @password`
+	args := pgx.NamedArgs{
+		"username": user.Username,
+		"password": hashPassword(user.Username, user.Password, "crab"),
+	}
+	if err := s.db.QueryRow(ctx, query, args).Scan(&user.Id); err != nil {
+		return nil, &UserNotFoundErr{}
+	}
+	return user, nil
+}
+
 func hashPassword(username string, password string, salt string) string {
 	return getMD5Hash(username + password + salt)
 }