After adding an item to the cart, when out of stock, remove from cart and reset client-side stock level

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

@@ -31,12 +31,23 @@ Darkswarm.factory 'Cart', (CurrentOrder, Variants, $timeout, $http, storage)->
       $http.post('/orders/populate', @data()).success (data, status)=>
         @saved()
         @update_running = false
+
+        @compareAndNotifyStockLevels data.stock_levels
+
         @popQueue() if @update_enqueued
 
       .error (response, status)=>
         @scheduleRetry(status)
         @update_running = false
 
+    compareAndNotifyStockLevels: (stockLevels) =>
+      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
+
     popQueue: =>
       @update_enqueued = false
       @scheduleUpdate()

spec/javascripts/unit/darkswarm/services/cart_spec.js.coffee

@@ -126,6 +126,27 @@ describe 'Cart service', ->
       $httpBackend.flush()
       expect(Cart.scheduleRetry).toHaveBeenCalled()
 
+  describe "verifying stock levels after update", ->
+    describe "when an item is out of stock", ->
+      it "reduces the quantity in the cart", ->
+        li = {variant: {id: 1}, quantity: 5}
+        spyOn(Cart, 'line_items_present').andReturn [li]
+        Cart.compareAndNotifyStockLevels({})
+        expect(li.quantity).toEqual 0
+        expect(li.max_quantity).toBeUndefined()
+
+      it "reduces the max_quantity in the cart", ->
+        li = {variant: {id: 1}, quantity: 5, max_quantity: 6}
+        spyOn(Cart, 'line_items_present').andReturn [li]
+        Cart.compareAndNotifyStockLevels({})
+        expect(li.max_quantity).toEqual 0
+
+      it "resets the count on hand available", ->
+        li = {variant: {id: 1, count_on_hand: 10}, quantity: 5}
+        spyOn(Cart, 'line_items_present').andReturn [li]
+        Cart.compareAndNotifyStockLevels({})
+        expect(li.variant.count_on_hand).toEqual 0
+
   it "pops the queue", ->
     Cart.update_enqueued = true
     spyOn(Cart, 'scheduleUpdate')