onSnapshotReceived modelled after onMongoConnect

lib/live-collection.js

@@ -1,5 +1,7 @@
 "use strict";
 
+var Halley                = require('halley/backbone');
+var Promise               = Halley.Promise;
 var _                     = require('underscore');
 var Backbone              = require('backbone');
 var backboneUrlResolver   = require('backbone-url-resolver');
@@ -27,6 +29,9 @@ module.exports = Backbone.Collection.extend({
     var defaults = { snapshot: true };
     options = _.extend(defaults, options);
 
+    // indicates if this LiveCollection has received at least one snapshot ever
+    this._snapshotReceived = false;
+
     if (options.client) {
       this.client = options.client;
     } else {
@@ -158,6 +163,8 @@ module.exports = Backbone.Collection.extend({
   },
 
   _resetOptional: function() {
+    this._snapshotReceived = false;
+
     if (!this.length) return;
 
     // Performance tweak
@@ -191,10 +198,33 @@ module.exports = Backbone.Collection.extend({
       this.reset(snapshot, options);
     }
 
+    this._snapshotReceived = true;
+
     this.trigger('sync');
     this.trigger('snapshot');
   },
 
+  onSnapshotReceived: function() {
+    var self = this;
+    if (this._snapshotReceived) {
+      debug('Snapshot already received, resolving immediately');
+      return Promise.resolve();
+    } else {
+      debug('Awaiting snapshot');
+      return new Promise(function(resolve, reject) {
+        self.once('snapshot', function() {
+          var resolved = true;
+          debug('Snapshot received');
+          resolve();
+        });
+        self.once('error', function(err) {
+          debug('Error received before promise could get resolved.');
+          reject(err);
+        });
+      });
+    }
+  },
+
   findExistingModel: function(id, newModel) {
     var existing = this.get(id);
     if(existing) return existing;