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;
+    }
+
+}