Implement PUT /user/{userId}/allowance/{allowanceId} (#52)

Closes #17

Reviewed-on: #52

backend/db.go

@@ -160,6 +160,33 @@ func (db *Db) DeleteAllowance(userId int, allowanceId int) error {
 	return nil
 }
 
+func (db *Db) UpdateAllowance(userId int, allowanceId int, allowance *UpdateAllowanceRequest) error {
+	// Check if the allowance exists for the user
+	count := 0
+	err := db.db.Query("select count(*) from allowances where id = ? and user_id = ?").
+		Bind(allowanceId, userId).ScanSingle(&count)
+	if err != nil {
+		return err
+	}
+	if count == 0 {
+		return errors.New("allowance not found")
+	}
+
+	tx, err := db.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.MustRollback()
+
+	err = tx.Query("update allowances set name=?, target=?, weight=? where id = ? and user_id = ?").
+		Bind(allowance.Name, allowance.Target, allowance.Weight, allowanceId, userId).
+		Exec()
+	if err != nil {
+		return err
+	}
+	return tx.Commit()
+}
+
 func (db *Db) CreateTask(task *CreateTaskRequest) (int, error) {
 	tx, err := db.db.Begin()
 	if err != nil {