Show a modal when available stock levels have reduced

app/assets/javascripts/darkswarm/services/cart.js.coffee

@@ -1,4 +1,4 @@
-Darkswarm.factory 'Cart', (CurrentOrder, Variants, $timeout, $http, storage)->
+Darkswarm.factory 'Cart', (CurrentOrder, Variants, $timeout, $http, $modal, $rootScope, storage)->
   # Handles syncing of current cart/order state to server
   new class Cart
     dirty: false
@@ -41,21 +41,30 @@ Darkswarm.factory 'Cart', (CurrentOrder, Variants, $timeout, $http, storage)->
         @update_running = false
 
     compareAndNotifyStockLevels: (stockLevels) =>
+      scope = $rootScope.$new(true)
+      scope.variants = []
+
+      # TODO: These changes to quantity/max_quantity trigger another cart update, which
+      #       is unnecessary.
+
       for li in @line_items_present()
         if !stockLevels[li.variant.id]?
-          alert "Variant out of stock: #{li.variant.id}"
           li.quantity = 0
           li.max_quantity = 0 if li.max_quantity?
           li.variant.count_on_hand = 0
+          scope.variants.push li.variant
         else
           if stockLevels[li.variant.id].quantity < li.quantity
-            alert "Variant quantity reduced: #{li.variant.id}"
             li.quantity = stockLevels[li.variant.id].quantity
+            scope.variants.push li.variant
           if stockLevels[li.variant.id].max_quantity < li.max_quantity
-            alert "Variant max_quantity reduced: #{li.variant.id}"
             li.max_quantity = stockLevels[li.variant.id].max_quantity
+            scope.variants.push li.variant
           li.variant.count_on_hand = stockLevels[li.variant.id].on_hand
 
+      if scope.variants.length > 0
+        $modal.open(templateUrl: "out_of_stock.html", scope: scope, windowClass: 'out-of-stock-modal')
+
     popQueue: =>
       @update_enqueued = false
       @scheduleUpdate()

app/assets/javascripts/templates/out_of_stock.html.haml

@@ -0,0 +1,10 @@
+%h3 Reduced stock available
+
+%p While you've been shopping, the stock levels for one or more of the products in your cart have reduced. Here's what's changed:
+
+%p{'ng-repeat' => "v in variants"}
+  %em {{ v.name_to_display }} - {{ v.unit_to_display }}
+  %span{'ng-if' => "v.count_on_hand == 0"}
+    is now out of stock.
+  %span{'ng-if' => "v.count_on_hand > 0"}
+    now only has {{ v.count_on_hand }} remaining.