Separated event listeners from resource fetching

refs https://github.com/TryGhost/Toolbox/issues/125

- The "fetchResources" method did way to many things extracted event listener setup logic to a separate method
- This allows to call out these stages as needed if we retreive resources separately from a cache of some sort and don't need to wait for the database response

core/server/services/url/Resources.js

@@ -55,13 +55,12 @@ class Resources {
         }
 
         const bridge = require('../../../bridge');
-        this.resourcesAPIVersion = bridge.getFrontendApiVersion();
+        const resourcesAPIVersion = bridge.getFrontendApiVersion();
-        this.resourcesConfig = require(`./configs/${this.resourcesAPIVersion}`);
+        this.resourcesConfig = require(`./configs/${resourcesAPIVersion}`);
     }
 
     /**
-     * @description Helper function to initialise data fetching. Each resource type needs to register resource/model
+     * @description Helper function to initialize data fetching.
-     *              events to get notified about updates/deletions/inserts.
      */
     fetchResources() {
         const ops = [];
@@ -75,6 +74,29 @@ class Resources {
 
             // NOTE: We are querying knex directly, because the Bookshelf ORM overhead is too slow.
             ops.push(this._fetch(resourceConfig));
+        });
+
+        return Promise.all(ops);
+    }
+
+    /**
+     * @description Each resource type needs to register resource/model events to get notified
+     * about updates/deletions/inserts.
+     *
+     * For example for a "tag" resource type with following configuration:
+     *  events: {
+     *     add: 'tag.added',
+     *     update: ['tag.edited', 'tag.attached', 'tag.detached'],
+     *     remove: 'tag.deleted'
+     *  }
+     * there would be:
+     * 1 event listener connected to  "_onResourceAdded"   handler and it's 'tag.added' event
+     * 3 event listeners connected to "_onResourceUpdated" handler and it's 'tag.edited', 'tag.attached', 'tag.detached' events
+     * 1 event listener connected to  "_onResourceRemoved" handler and it's 'tag.deleted' event
+     */
+    initEvenListeners() {
+        _.each(this.resourcesConfig, (resourceConfig) => {
+            this.data[resourceConfig.type] = [];
 
             this._listenOn(resourceConfig.events.add, (model) => {
                 return this._onResourceAdded.bind(this)(resourceConfig.type, model);
@@ -96,8 +118,6 @@ class Resources {
                 return this._onResourceRemoved.bind(this)(resourceConfig.type, model);
             });
         });
-
-        return Promise.all(ops);
     }
 
     /**

core/server/services/url/UrlService.js

@@ -288,6 +288,7 @@ class UrlService {
      */
     init() {
         this.resources.fetchResources();
+        this.resources.initEvenListeners();
         // CASE: all resources are fetched, start the queue
         this.queue.start({
             event: 'init',