Adds onInsert callback to reindex() static call. (#87)

* Allows the usage of a callback in reindex() static call to access exactly which entity is being indexed to Algolia

* Improves efficiency of onInsert callback

* Actually updates the README. My bad.

README.md

@@ -402,6 +402,17 @@ To keep settings that you set on the Algolia dashboard when reindexing and setti
 Contact::reindex(true, true, true);
 ```
 
+To implement a callback that gets called everytime a batch of entities is indexed:
+
+```php
+Contact::reindex(true, true, false, function ($entities)
+{
+    foreach ($entities as $entity)
+    {
+        var_dump($entity->id); // Contact::$id
+    }
+});
+```
 
 ### Clearing an Index
 

src/AlgoliaEloquentTrait.php

@@ -18,7 +18,7 @@ trait AlgoliaEloquentTrait
      * @param bool $setSettings
      * @param bool $mergeOldSettings
      */
-    public function _reindex($safe = true, $setSettings = true, $mergeOldSettings = false)
+    public function _reindex($safe = true, $setSettings = true, $mergeOldSettings = false, \Closure $onInsert = null)
     {
         /** @var \AlgoliaSearch\Laravel\ModelHelper $modelHelper */
         $modelHelper = App::make('\AlgoliaSearch\Laravel\ModelHelper');
@@ -31,18 +31,27 @@ public function _reindex($safe = true, $setSettings = true, $mergeOldSettings =
             $this->_setSettings($setToTmpIndices, $mergeOldSettings);
         }
 
-        static::chunk(100, function ($models) use ($indicesTmp, $modelHelper) {
+        static::chunk(100, function ($models) use ($indicesTmp, $modelHelper, $onInsert) {
             /** @var \AlgoliaSearch\Index $index */
             foreach ($indicesTmp as $index) {
-                $records = [];
+                $records         = [];
+                $recordsAsEntity = [];
 
                 foreach ($models as $model) {
                     if ($modelHelper->indexOnly($model, $index->indexName)) {
                         $records[] = $model->getAlgoliaRecordDefault($index->indexName);
+
+                        if ($onInsert && is_callable($onInsert)) {
+                            $recordsAsEntity[] = $model;
+                        }
                     }
                 }
 
                 $index->addObjects($records);
+
+                if ($onInsert && is_callable($onInsert)) {
+                    call_user_func_array($onInsert, [$recordsAsEntity]);
+                }
             }
 
         });