IconHelper: start to separate concerns in forms

One new small helper class for this purpose

library/Director/Web/Form/IconHelper.php

@@ -0,0 +1,85 @@
+<?php
+
+namespace Icinga\Module\Director\Web\Form;
+
+use Icinga\Exception\ProgrammingError;
+
+/**
+ * Icon helper class
+ *
+ * Should help to reduce redundant icon-lookup code. Currently with hardcoded
+ * icons only, could easily provide support for all of them as follows:
+ *
+ * $confFile = Icinga::app()
+ *     ->getApplicationDir('fonts/fontello-ifont/config.json');
+ *
+ * $font = json_decode(file_get_contents($confFile));
+ * // 'icon-' is to be found in $font->css_prefix_text
+ * foreach ($font->glyphs as $icon) {
+ * // $icon->css (= 'help') -> 0x . dechex($icon->code)
+ * }
+ */
+class IconHelper
+{
+    private $icons = array(
+        'minus'  => 'e806',
+        'trash'  => 'e846',
+        'plus'   => 'e805',
+        'cancel' => 'e804',
+        'help'   => 'e85b',
+    );
+
+    private $mappedUtf8Icons;
+
+    private $reversedUtf8Icons;
+
+    private static $instance;
+
+    public function __construct()
+    {
+        $this->prepareIconMappings();
+    }
+
+    public static function instance()
+    {
+        if (self::$instance === null) {
+            self::$instance = new static;
+        }
+
+        return self::$instance;
+    }
+
+    public function characterIconName($character)
+    {
+        if (array_key_exists($character, $this->reversedUtf8Icons)) {
+            return $this->reversedUtf8Icons[$character];
+        } else {
+            throw new ProgrammingError('There is no mapping for the given character');
+        }
+    }
+
+    protected function hexToCharacter($hex)
+    {
+        return json_decode('"\u' . $hex . '"');
+    }
+
+    public function iconCharacter($name)
+    {
+        if (array_key_exists($name, $this->mappedUtf8Icons)) {
+            return $this->mappedUtf8Icons[$name];
+        } else {
+            return $this->mappedUtf8Icons['help'];
+        }
+    }
+
+    protected function prepareIconMappings()
+    {
+        $this->mappedUtf8Icons = array();
+        $this->reversedUtf8Icons = array();
+        foreach ($this->icons as $name => $hex) {
+            $character = $this->hexToCharacter($hex);
+            $this->mappedUtf8Icons[$name] = $character;
+            $this->reversedUtf8Icons[$character] = $name;
+        }
+    }
+}