Added metrics

Business/Marketing/Metrics.php

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+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 7.1
+ *
+ * @category   TBD
+ * @package    TBD
+ * @copyright  Dennis Eichhorn
+ * @license    OMS License 1.0
+ * @version    1.0.0
+ * @link       http://orange-management.com
+ */
+declare(strict_types=1);
+
+namespace phpOMS\Business\Marketing;
+
+/**
+ * Net Promoter Score
+ *
+ * @category   Framework
+ * @package    phpOMS\Business
+ * @license    OMS License 1.0
+ * @link       http://orange-management.com
+ * @since      1.0.0
+ */
+class Metrics {
+    /**
+     * Calculate customer retention
+     * 
+     * @param int $ce Customer at the end of the period
+     * @param int $cn New customers during period
+     * @param int $cs Customers at the start of the period
+     *
+     * @return float
+     *
+     * @since  1.0.0
+     */
+    public static function getCustomerRetention(int $ce, int $cn, int $cs) : float
+    {
+        return ($ce - $cn) / $cs;
+    }
+}

Business/Programming/Metrics.php

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+<?php
+/**
+ * Orange Management
+ *
+ * PHP Version 7.1
+ *
+ * @category   TBD
+ * @package    TBD
+ * @copyright  Dennis Eichhorn
+ * @license    OMS License 1.0
+ * @version    1.0.0
+ * @link       http://orange-management.com
+ */
+declare(strict_types=1);
+namespace phpOMS\Business\Programming;
+/**
+ * Programming metrics
+ *
+ * @category   Framework
+ * @package    phpOMS\Business
+ * @license    OMS License 1.0
+ * @link       http://orange-management.com
+ * @since      1.0.0
+ */
+class Metrics {
+    /**
+     * Calculate ABC metric score
+     *
+     * @latex  r = \sqrt{a^{2} + b^{2} + c^{2}}
+     *
+     * @param int $a Assignments
+     * @param int $b Branches
+     * @param int $c Conditionals
+     *
+     * @return int
+     *
+     * @since  1.0.0
+     */
+    public static function abcScore(int $a, int $b, int $c) : int
+    {
+        return (int) sqrt($a*$a+$b*$b+$c*$c);
+    }
+}