tabel user

internal/store/user_store.go

@@ -2,13 +2,18 @@ package store
 
 import (
 	"context"
+	"errors"
 	"sync"
 
 	"5803025020/w04/internal/models"
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 )
 
+// ErrUsernameTaken dikembalikan saat Create() gagal karena username sudah dipakai (unique constraint).
+var ErrUsernameTaken = errors.New("username already exists")
+
 type UserStore struct {
 	conn *pgx.Conn
 	mu   *sync.Mutex
@@ -34,7 +39,14 @@ func (s *UserStore) Create(ctx context.Context, user *models.User) error {
 
 	query := `INSERT INTO users (id, username, password_hash) VALUES ($1, $2, $3)`
 	_, err := s.conn.Exec(ctx, query, user.ID, user.Username, user.PasswordHash)
-	return err
+	if err != nil {
+		var pgErr *pgconn.PgError
+		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
+			return ErrUsernameTaken
+		}
+		return err
+	}
+	return nil
 }
 
 func (s *UserStore) GetByUsername(ctx context.Context, username string) (*models.User, error) {