[FIX] point_of_sale: improve refunding order with single item

For simplicity, when the order has single item (refundable quantity
of 1) and has single line, we just assume that it's fully refundable.
No need to ask the user how much they want to refund.

Part-of: odoo/odoo#77903

addons/point_of_sale/static/src/js/Screens/TicketScreen/TicketScreen.js

@@ -193,6 +193,10 @@ odoo.define('point_of_sale.TicketScreen', function (require) {
                 return this.render();
             }
 
+            if (this._doesOrderHaveSoleItem(order)) {
+                this._prepareAutoRefundOnOrder(order);
+            }
+
             const customer = order.get_client();
 
             // Select the lines from toRefundLines (can come from different orders)
@@ -356,6 +360,7 @@ odoo.define('point_of_sale.TicketScreen', function (require) {
         getHasItemsToRefund() {
             const order = this.getSelectedSyncedOrder();
             if (!order) return false;
+            if (this._doesOrderHaveSoleItem(order)) return true;
             const total = Object.values(this.env.pos.toRefundLines)
                 .filter(
                     (toRefundDetail) =>
@@ -367,6 +372,24 @@ odoo.define('point_of_sale.TicketScreen', function (require) {
         }
         //#endregion
         //#region PRIVATE METHODS
+        _doesOrderHaveSoleItem(order) {
+            const orderlines = order.get_orderlines();
+            if (orderlines.length !== 1) return false;
+            const theOrderline = orderlines[0];
+            const refundableQty = theOrderline.get_quantity() - theOrderline.refunded_qty;
+            return this.env.pos.isProductQtyZero(refundableQty - 1);
+        }
+        _prepareAutoRefundOnOrder(order) {
+            const selectedOrderlineId = this.getSelectedOrderlineId();
+            const orderline = order.orderlines.models.find((line) => line.id == selectedOrderlineId);
+            if (!orderline) return;
+
+            const toRefundDetail = this._getToRefundDetail(orderline);
+            const refundableQty = orderline.get_quantity() - orderline.refunded_qty;
+            if (this.env.pos.isProductQtyZero(refundableQty - 1)) {
+                toRefundDetail.qty = 1;
+            }
+        }
         /**
          * Returns the corresponding toRefundDetail of the given orderline.
          * SIDE-EFFECT: Automatically creates a toRefundDetail object for