feat: add GetByEmail, make username nullable

backend/internal/domain/user.go

@@ -27,7 +27,7 @@ func (u *User) NormalizedUsername() string {
 func (u *User) Validate() error {
 	return validation.ValidateStruct(u,
 		validation.Field(&u.UUID, validation.Required),
-		validation.Field(&u.Username, validation.Required, validation.Length(3, 20)),
+		validation.Field(&u.Username, validation.Length(3, 20)),
 		validation.Field(&u.Password, validation.Required, validation.Length(6, 100)),
 		validation.Field(&u.Email, validation.Required, is.Email),
 	)
@@ -36,6 +36,7 @@ func (u *User) Validate() error {
 type UserRepository interface {
 	GetByID(context.Context, int64) (User, error)
 	GetByUsername(context.Context, string) (User, error)
+	GetByEmail(context.Context, string) (User, error)
 	CreateOrUpdate(context.Context, *User) error
 	Delete(context.Context, int64) error
 }

backend/internal/repository/postgres_user.go

@@ -78,15 +78,31 @@ func (p *postgresUserRepository) GetByUsername(ctx context.Context, username str
 	return users[0], nil
 }
 
-func (p *postgresUserRepository) CreateOrUpdate(ctx context.Context, u *domain.User) error {
-	if err := u.Validate(); err != nil {
-		return err
+func (p *postgresUserRepository) GetByEmail(ctx context.Context, email string) (domain.User, error) {
+	query := `
+		SELECT id, uuid, username, password, email, created_at, updated_at, is_active  
+		FROM users
+		WHERE email = $1`
+
+	users, err := p.fetch(ctx, query, email)
+	if err != nil {
+		return domain.User{}, err
+	}
+	if len(users) == 0 {
+		return domain.User{}, domain.ErrNotFound
+	}
+	return users[0], nil
 }
 
+func (p *postgresUserRepository) CreateOrUpdate(ctx context.Context, u *domain.User) error {
 	if strings.TrimSpace(u.UUID) == "" {
 		u.UUID = uuid.New().String()
 	}
 
+	if err := u.Validate(); err != nil {
+		return err
+	}
+
 	u.NormalizedUsername()
 
 	query := `  

backend/migrations/00001_create_user_table.sql

@@ -2,7 +2,7 @@
 CREATE TABLE users (
     id SERIAL PRIMARY KEY,
     uuid UUID NOT NULL,
-    username TEXT NOT NULL,
+    username TEXT NULL,
     password TEXT NOT NULL,
     email TEXT NOT NULL,
     created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),