Add Addresses class

Fixes #11

src/Helpers/Addresses.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace Opdavies\GmailFilterBuilder\Helpers;
+
+/**
+ * A helper class for loading addresses from separate files.
+ */
+class Addresses
+{
+    /**
+     * The name of the default directory containing the address files.
+     */
+    const DIRECTORY_NAME = '.gmail-filters';
+
+    /**
+     * Load addresses from a file.
+     *
+     * @param string $filename The filename to load.
+     *
+     * @return array
+     */
+    public static function load($filename = 'my-addresses.php')
+    {
+        if (file_exists($file = (new static())->getDirectoryPath() . $filename)) {
+            return include $file;
+        }
+
+        return [];
+    }
+
+    /**
+     * Get the directory name containing the addresses file.
+     *
+     * Defaults to a .gmail-filters directory within the user's home directory.
+     *
+     * @return string
+     */
+    protected function getDirectoryPath()
+    {
+        return getenv('HOME') . DIRECTORY_SEPARATOR . self::DIRECTORY_NAME . DIRECTORY_SEPARATOR;
+    }
+}