Add reduce function to QueryBuilder

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

src/Function/Reduce.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Function;
+
+class Reduce extends Base {
+
+    /**
+     * @var array $settings
+     */
+    private $settings;
+
+    /**
+     * @var array $identity
+     */
+    private $identity;
+
+    public function __construct(array $settings, array $identity)
+    {
+        $this->settings = $settings;
+        $this->identity = $identity;
+    }
+
+    public function __toString()
+    {
+        //reduce(fn: (r, accumulator) => ({sum: r._value + accumulator.sum}), identity: {sum: 0})
+
+        return '|> reduce(fn: (r, accumulator) => ({' . implode(', ', $this->formatSettings($this->settings)) . '}), ' . 
+            'identity: {' . implode(', ', $this->format($this->identity)) . '}) ';
+    }
+
+    protected function formatSettings(array $settings)
+    {
+        array_walk($settings, function(&$value, $key) {
+			$value = $key . ': ' . $value;
+		});
+
+        return $settings;
+    }
+
+    protected function format(array $settings)
+    {
+        array_walk($settings, function(&$value, $key) {
+			$value = $key . ': ' . (is_string($value) ? '"' . $value . '"' : $value);
+		});
+
+        return $settings;
+    }
+
+}

src/QueryBuilder.php

@@ -6,6 +6,7 @@ use Arendsen\FluxQueryBuilder\Expression\KeyValue;
 use Arendsen\FluxQueryBuilder\Function\Filter;
 use Arendsen\FluxQueryBuilder\Function\From;
 use Arendsen\FluxQueryBuilder\Function\Range;
+use Arendsen\FluxQueryBuilder\Function\Reduce;
 use Exception;
 
 class QueryBuilder {
@@ -13,10 +14,12 @@ class QueryBuilder {
     const FLUX_PART_FROM = 'from';
     const FLUX_PART_RANGE = 'range';
     const FLUX_PART_FILTERS = 'filters';
+    const FLUX_PART_REDUCE = 'reduce';
 
     const PARTS = [
         self::FLUX_PART_FROM,
         self::FLUX_PART_RANGE,
+        self::FLUX_PART_REDUCE,
         self::FLUX_PART_FILTERS
     ];
 
@@ -91,6 +94,15 @@ class QueryBuilder {
         return $this;
     }
 
+    public function addReduce(array $settings, array $identity): QueryBuilder
+    {
+        $this->addToQueryArray(
+            self::FLUX_PART_REDUCE,
+            new Reduce($settings, $identity)
+        );
+        return $this;
+    }
+
     protected function addToQuery($key, $query)
     {
         $this->fluxQueryParts[$key] = $query;

tests/Function/ReduceFunctionTest.php

@@ -0,0 +1,18 @@
+<?php
+declare(strict_types=1);
+
+use Arendsen\FluxQueryBuilder\Function\Reduce;
+use PHPUnit\Framework\TestCase;
+
+final class ReduceFunctionTest extends TestCase {
+
+    public function testSimpleReduce()
+    {
+        $expression = new Reduce(['sum' => 'r._value + accumulator.sum'], ['sum' => 0]);
+
+        $query = '|> reduce(fn: (r, accumulator) => ({sum: r._value + accumulator.sum}), identity: {sum: 0}) ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+
+}