lib: Add a not yet customizable node renderer

library/Icinga/Data/Tree/NodeRenderer.php

@@ -0,0 +1,58 @@
+<?php
+// {{{ICINGA_LICENSE_HEADER}}}
+// {{{ICINGA_LICENSE_HEADER}}
+
+namespace Icinga\Data\Tree;
+
+use Exception;
+use RecursiveIteratorIterator;
+use RuntimeException;
+
+/**
+ * A not yet customizable node renderer
+ */
+class NodeRenderer extends RecursiveIteratorIterator
+{
+    protected $content = array();
+
+    public function __construct(NodeInterface $node)
+    {
+        parent::__construct($node, RecursiveIteratorIterator::SELF_FIRST);
+    }
+
+    public function beginIteration()
+    {
+        $this->content[] = '<ul>';
+    }
+
+    public function endIteration()
+    {
+        $this->content[] = '</ul>';
+    }
+
+    public function beginChildren()
+    {
+        $this->content[] = '<ul>';
+    }
+
+    public function endChildren()
+    {
+        $this->content[] = '</ul>';
+    }
+
+    public function render($callback)
+    {
+        if (! is_callable($callback)) {
+            throw new RuntimeException('Callable expected');
+        }
+        foreach ($this as $node) {
+            try {
+                $content = call_user_func($callback, $node);
+            } catch (Exception $e) {
+                throw new RuntimeException($e);
+            }
+            $this->content[] = $content;
+        }
+        return implode("\n", $this->content);
+    }
+}