added bucket script aggregation

src/Aggregation/Pipeline/BucketScriptAggregation.php

+<?php
+
+/*
+ * This file is part of the ONGR package.
+ *
+ * (c) NFQ Technologies UAB <info@nfq.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace ONGR\ElasticsearchDSL\Aggregation\Pipeline;
+
+/**
+ * Class representing Bucket Script Pipeline Aggregation.
+ *
+ * @link https://goo.gl/miVxcx
+ */
+class BucketScriptAggregation extends AbstractPipelineAggregation
+{
+    /**
+     * @var string
+     */
+    private $script;
+
+    /**
+     * @param string $name
+     * @param array  $bucketsPath
+     * @param string $script
+     */
+    public function __construct($name, $bucketsPath, $script = null)
+    {
+        parent::__construct($name, $bucketsPath);
+        $this->setScript($script);
+    }
+
+    /**
+     * @return string
+     */
+    public function getScript()
+    {
+        return $this->script;
+    }
+
+    /**
+     * @param string $script
+     */
+    public function setScript($script)
+    {
+        $this->script = $script;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getType()
+    {
+        return 'bucket_script';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getArray()
+    {
+        if (!$this->getScript()) {
+            throw new \LogicException(
+                sprintf(
+                    '`%s` aggregation must have script set.',
+                    $this->getName()
+                )
+            );
+        }
+
+        $out = [
+            'buckets_path' => $this->getBucketsPath(),
+            'script' => $this->getScript(),
+        ];
+
+        return $out;
+    }
+}