fix: should display an error instead of taking absolute (#28)

internal/api/handler/customer_handler.go

@@ -216,6 +216,10 @@ func (h customerHandler) TransferMoney(c *gin.Context) {
 
 	if err := h.transactionService.TransferMoney(fromAccount, toAccount, amount); err != nil {
 		switch err := err.Error(); err {
+		case "amount must be greater than 0":
+			h.Form.Errors["amount"] = "Amount must be greater than 0"
+			c.HTML(http.StatusUnprocessableEntity, "account/transfer_money_form", h)
+			return
 		case "not enough money":
 			h.Form.Errors["from_account"] = "You do not have enough money in this account"
 			c.HTML(http.StatusUnprocessableEntity, "account/transfer_money_form", h)

internal/service/transaction_service.go

@@ -116,7 +116,9 @@ func (ts transactionService) Create(transaction *domain.Transaction) error {
 
 func (s transactionService) TransferMoney(from domain.Account, to domain.Account, amount float64) error {
 	return persistence.DB.Transaction(func(tx *gorm.DB) error {
-		amount = math.Abs(amount)
+		if amount <= 0 {
+			return errors.New("amount must be greater than 0")
+		}
 
 		if from.Balance < amount {
 			return errors.New("not enough money")