Add mean() method to Query Builder

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Functions/Mean.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Functions;
+
+use Arendsen\FluxQueryBuilder\Type;
+use Arendsen\FluxQueryBuilder\Type\ArrayType;
+
+class Mean extends Base
+{
+    /**
+     * @var string $column
+     */
+    private $column;
+
+    public function __construct(string $column = '_value')
+    {
+        $this->column = $column;
+    }
+
+    public function __toString()
+    {
+        $input = new ArrayType(array_filter([
+            'column' => !empty($this->column) && $this->column !== '_value'  ?
+                new Type($this->column) : null
+        ]));
+
+        return '|> mean(' . $input . ') ';
+    }
+}

src/QueryBuilder.php

@@ -14,6 +14,7 @@ use Arendsen\FluxQueryBuilder\Functions\Sort;
 use Arendsen\FluxQueryBuilder\Functions\Map;
 use Arendsen\FluxQueryBuilder\Functions\Group;
 use Arendsen\FluxQueryBuilder\Functions\Limit;
+use Arendsen\FluxQueryBuilder\Functions\Mean;
 use Arendsen\FluxQueryBuilder\Functions\Window;
 
 class QueryBuilder
@@ -27,6 +28,7 @@ class QueryBuilder
     public const FLUX_PART_GROUP = 'group';
     public const FLUX_PART_LIMIT = 'limit';
     public const FLUX_PART_WINDOW = 'window';
+    public const FLUX_PART_MEAN = 'mean';
     public const FLUX_PART_UNWINDOW = 'unwindow';
     public const FLUX_PART_AGGREGATEWINDOW = 'aggregateWindow';
 
@@ -35,6 +37,7 @@ class QueryBuilder
         self::FLUX_PART_RANGE,
         self::FLUX_PART_REDUCE,
         self::FLUX_PART_WINDOW,
+        self::FLUX_PART_MEAN,
         self::FLUX_PART_FILTERS,
         self::FLUX_PART_MAP,
         self::FLUX_PART_SORT,
@@ -177,16 +180,25 @@ class QueryBuilder
 
     public function addWindow($every, array $options = []): QueryBuilder
     {
-        $this->addToQueryArray(
+        $this->addToQuery(
             self::FLUX_PART_WINDOW,
             new Window($every, $options)
         );
         return $this;
     }
 
+    public function addMean(?string $column = '')
+    {
+        $this->addToQuery(
+            self::FLUX_PART_MEAN,
+            new Mean($column)
+        );
+        return $this;
+    }
+
     public function addUnWindow()
     {
-        $this->addToQueryArray(
+        $this->addToQuery(
             self::FLUX_PART_UNWINDOW,
             new Window('inf')
         );

tests/Functions/MeanFunctionTest.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Functions;
+
+use Arendsen\FluxQueryBuilder\Functions\Mean;
+use PHPUnit\Framework\TestCase;
+
+final class MeanFunctionTest extends TestCase
+{
+    public function testSimpleMean()
+    {
+        $expression = new Mean();
+
+        $query = '|> mean() ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+
+    public function testWithParameterColumn()
+    {
+        $expression = new Mean('test');
+
+        $query = '|> mean(column: "test") ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+}

tests/Generic/QueryBuilderTest.php

@@ -123,12 +123,13 @@ final class QueryBuilderTest extends TestCase
             ->addRangeStart(new DateTime('2022-08-12 17:31:00'))
             ->addWindow('20s')
             ->addReduce(['count' => new MathType('accumulator.count + 1')], ['count' => 0])
+            ->addMean()
             ->addFilter(KeyValue::setGreaterOrEqualTo('count', 1)->andGreaterOrEqualTo('count2', 2))
             ->addUnWindow();
 
         $expectedQuery = 'from(bucket: "test_bucket") |> range(start: time(v: 2022-08-12T17:31:00Z)) ' .
         '|> reduce(fn: (r, accumulator) => ({count: accumulator.count + 1}), identity: {count: 0}) ' .
-        '|> window(every: 20s) |> filter(fn: (r) => r._measurement == "test_measurement") ' .
+        '|> window(every: 20s) |> mean() |> filter(fn: (r) => r._measurement == "test_measurement") ' .
         '|> filter(fn: (r) => r.count >= 1 and r.count2 >= 2) |> window(every: inf) ';
 
         $this->assertEquals($expectedQuery, $queryBuilder->build());