better error handling

internal/db/mock.go

@@ -31,7 +31,7 @@ func (d *mockDB) CreateShare(ctx context.Context, share *types.Share) error {
 
 func (d *mockDB) DeleteShare(ctx context.Context, slug string) error {
 	if d.shares[slug] == nil {
-		return errors.New("share does not exist")
+		return types.ErrShareNotFound
 	}
 	delete(d.shares, slug)
 	return nil

internal/db/sql.go

@@ -79,10 +79,20 @@ func (db *sqlDB) CreateShare(ctx context.Context, share *types.Share) error {
 }
 
 func (db *sqlDB) DeleteShare(ctx context.Context, slug string) error {
-	_, err := db.db.ExecContext(ctx, "DELETE FROM shares WHERE slug = ?", slug)
+	result, err := db.db.ExecContext(ctx, "DELETE FROM shares WHERE slug = ?", slug)
 	if err != nil {
 		return err
 	}
+
+	rowsAffected, err := result.RowsAffected()
+	if err != nil {
+		return err
+	}
+
+	if rowsAffected == 0 {
+		return types.ErrShareNotFound
+	}
+
 	return nil
 }