fix: disable add-to-basket when quantity is zero (#1066)

(cherry picked from commit d655d63)

src/app/core/facades/product-context.facade.ts

@@ -259,6 +259,25 @@ export class ProductContextFacade extends RxState<ProductContext> implements OnD
       (state, minOrderQuantity) => (state.quantity ??= minOrderQuantity)
     );
 
+    this.connect(
+      'quantity',
+      this.select('children').pipe(
+        map(children => Object.values(children)),
+        skipWhile(children => !children?.length),
+        map(children =>
+          children.reduce(
+            (sum, child) =>
+              sum +
+              (Number.isInteger(child.quantity) && !child.hasQuantityError && !child.hasProductError
+                ? child.quantity
+                : 0),
+            0
+          )
+        ),
+        distinctUntilChanged()
+      )
+    );
+
     this.connect(
       'hasProductError',
       this.select('product').pipe(

src/app/shared/components/product/product-add-to-basket/product-add-to-basket.component.spec.ts

@@ -24,6 +24,7 @@ describe('Product Add To Basket Component', () => {
     context = mock(ProductContextFacade);
     when(context.select('displayProperties', 'addToBasket')).thenReturn(of(true));
     when(context.select('product')).thenReturn(of({} as ProductView));
+    when(context.select('quantity')).thenReturn(of(1));
     when(context.select('hasQuantityError')).thenReturn(of(false));
     when(context.select('hasProductError')).thenReturn(of(false));
 
@@ -78,6 +79,12 @@ describe('Product Add To Basket Component', () => {
     expect(element.querySelector('button').disabled).toBeTruthy();
   });
 
+  it('should show disabled button when context has no quantity', () => {
+    when(context.select('quantity')).thenReturn(of(0));
+    fixture.detectChanges();
+    expect(element.querySelector('button').disabled).toBeTruthy();
+  });
+
   it('should use default translation when nothing is configured', () => {
     fixture.detectChanges();
     expect(element.textContent).toMatchInlineSnapshot(`"product.add_to_cart.link"`);

src/app/shared/components/product/product-add-to-basket/product-add-to-basket.component.ts

@@ -61,11 +61,11 @@ export class ProductAddToBasketComponent implements OnInit, OnDestroy {
 
     const hasQuantityError$ = this.context.select('hasQuantityError');
     const hasProductError$ = this.context.select('hasProductError');
-    this.buttonDisabled$ = combineLatest([
-      this.displaySpinner$.pipe(startWith(false)),
-      hasQuantityError$.pipe(),
-      hasProductError$.pipe(),
-    ]).pipe(map(conditions => conditions.some(c => !!c)));
+    const hasNoQuantity$ = this.context.select('quantity').pipe(map(quantity => quantity <= 0));
+    const loading$ = this.displaySpinner$.pipe(startWith(false));
+    this.buttonDisabled$ = combineLatest([loading$, hasQuantityError$, hasProductError$, hasNoQuantity$]).pipe(
+      map(conditions => conditions.some(c => !!c))
+    );
   }
 
   addToBasket() {