API: Rig up mutation { update }

api/graph/schema.resolvers.go

@@ -182,7 +182,27 @@ func (r *mutationResolver) Create(ctx context.Context, files []*graphql.Upload,
 }
 
 func (r *mutationResolver) Update(ctx context.Context, id string, visibility model.Visibility) (*model.Paste, error) {
-	panic(fmt.Errorf("not implemented"))
+	var paste model.Paste
+
+	if err := database.WithTx(ctx, nil, func(tx *sql.Tx) error {
+		row := tx.QueryRowContext(ctx, `
+			UPDATE paste
+			SET visibility = $1
+			WHERE sha = $2 AND user_id = $3
+			RETURNING
+				id, sha, created, user_id, visibility;`,
+			strings.ToLower(visibility.String()),
+			id, auth.ForContext(ctx).UserID)
+		return row.Scan(&paste.PKID, &paste.ID,
+			&paste.Created, &paste.UserID, &paste.RawVisibility)
+	}); err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	return &paste, nil
 }
 
 func (r *mutationResolver) Delete(ctx context.Context, id string) (*model.Paste, error) {