Do not allow invalid quantity to reach model, triggering server update

app/assets/javascripts/darkswarm/directives/on_hand.js.coffee

@@ -1,9 +1,19 @@
 Darkswarm.directive "ofnOnHand", ->
   restrict: 'A'
-  link: (scope, elem, attr) ->
-    on_hand = parseInt(attr.ofnOnHand)
-    elem.bind 'change', (e) ->
-      if parseInt(elem.val()) > on_hand
-        scope.$apply ->
-          alert t('insufficient_stock', {on_hand: on_hand})
-          elem.val(on_hand)
+  require: "ngModel"
+
+  link: (scope, elem, attr, ngModel) ->
+    # In cases where this field gets its value from the HTML element rather than the model,
+    # initialise the model with the HTML value.
+    if scope.$eval(attr.ngModel) == undefined
+      ngModel.$setViewValue elem.val()
+
+    ngModel.$parsers.push (viewValue) ->
+      on_hand = parseInt(attr.ofnOnHand)
+      if parseInt(viewValue) > on_hand
+        alert t('insufficient_stock', {on_hand: on_hand})
+        viewValue = on_hand
+        ngModel.$setViewValue viewValue
+        ngModel.$render()
+
+      viewValue

app/views/spree/orders/_line_item.html.haml

@@ -30,7 +30,7 @@
     -#   "price-breakdown-placement" => "left",
     -#   "price-breakdown-animation" => true}
   %td.text-center.cart-item-quantity{"data-hook" => "cart_item_quantity"}
-    = item_form.number_field :quantity, :min => 0, "ofn-on-hand" => variant.on_hand, :class => "line_item_quantity", :size => 5
+    = item_form.number_field :quantity, :min => 0, "ofn-on-hand" => variant.on_hand, "ng-model" => "line_item_#{line_item.id}", :class => "line_item_quantity", :size => 5
   %td.cart-item-total.text-right{"data-hook" => "cart_item_total"}
     = line_item.display_amount_with_adjustments.to_html unless line_item.quantity.nil?