Add stats aggregation

src/Aggregation/StatsAggregation.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Erichard\ElasticQueryBuilder\Aggregation;
+
+/**
+ * @see https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-metrics-stats-aggregation.html
+ */
+class StatsAggregation extends MetricAggregation
+{
+    protected function getType(): string
+    {
+        return 'stats';
+    }
+}

tests/Aggregation/StatsAggregationTest.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Erichard\ElasticQueryBuilder\Aggregation;
+
+use Erichard\ElasticQueryBuilder\Aggregation\StatsAggregation;
+use PHPUnit\Framework\TestCase;
+
+class StatsAggregationTest extends TestCase
+{
+    public function testItBuildTheAggregationUsingAField(): void
+    {
+        $query = new StatsAggregation('price');
+        $query->setField('price');
+
+        $this->assertEquals([
+            'stats' => [
+                'field' => 'price',
+            ],
+        ], $query->build());
+    }
+
+    public function testItBuildTheAggregationUsingAScript(): void
+    {
+        $query = new StatsAggregation('price');
+        $query->setScript('doc.price.value');
+
+        $this->assertEquals([
+            'stats' => [
+                'script' => [
+                    'source' => 'doc.price.value',
+                ],
+            ],
+        ], $query->build());
+    }
+
+    public function testWithFieldName(): void
+    {
+        $query = new StatsAggregation('price');
+
+        $this->assertEquals([
+            'stats' => [
+                'field' => 'price',
+            ],
+        ], $query->build());
+    }
+
+    public function testItBuildTheAggregationWithMissingValue(): void
+    {
+        $query = new StatsAggregation('price', 'price');
+        $query->setMissing(10);
+
+        $this->assertEquals([
+            'stats' => [
+                'field' => 'price',
+                'missing' => 10,
+            ],
+        ], $query->build());
+    }
+}