fix(vuex-middleware): impossible to use ecommerce in vuex

the ecommerce is different from the others and needs a special treatment

Author: MatteoGabriele

docs/vuex.md

@@ -88,9 +88,11 @@ The way we can construct the track method is just by creating an array and the f
 * social
 * time
 * untracked
-* ecommerce
+* ecommerce (*)
 * commands
 
+**(*) pay attention to the ecommerce API at the bottom of this page, since it has a different structure**
+
 the second parameter will be our data constructed the same way as we were inside a component, for example:
 
 ```js
@@ -166,3 +168,24 @@ commit('someAction', {
   }
 })
 ```
+
+### Ecommerce and Vuex
+
+Because of its differnet API nature, the ecommerce plugin needs to be called as it in the original Google Analytics documentation.
+
+```js
+commit('someAction', {
+  meta: {
+    analytics: [
+       ['ecommerce:addItem', {
+          id: '1234',
+          name: 'Fluffy Pink Bunnies',
+          sku: 'DD23444',
+          category: 'Party Toys',
+          price: '11.99',
+          quantity: '1'
+        }]
+    ]
+  }
+})
+```

src/vuex-middleware.js

@@ -13,14 +13,38 @@ export default store => {
     }
 
     analytics.forEach(event => {
-      const type = event.shift()
+      let method
+      let type = event.shift()
+
       const props = event
 
+      if (type.includes(':')) {
+        [type, method] = type.split(':')
+      }
+
       if (!(type in lib)) {
-        throw new Error(`The type "${type}" doesn't exist.`)
+        throw new Error(
+          `[vue-analytics:vuex] The type "${type}" doesn't exist.`
+        )
+      }
+
+      if (method && !(method in lib[type])) {
+        throw new Error(
+          `[vue-analytics:vuex] The type "${type}" has not method "${method}".`
+        )
+      }
+
+      if (type === 'ecommerce' && !method) {
+        throw new Error(
+          `[vue-analytics:vuex] The type "${type}" needs to call a method. Check documentation.`
+        )
       }
 
-      lib[type](...props)
+      if (method) {
+        lib[type][method](...props)
+      } else {
+        lib[type](...props)
+      }
     })
   })
 }