doc/lib: Add `SectionFilterIterator' for iterating over sections that are part of a particular chapter

refs #4820

modules/doc/library/Doc/SectionFilterIterator.php

@@ -0,0 +1,68 @@
+<?php
+// {{{ICINGA_LICENSE_HEADER}}}
+// {{{ICINGA_LICENSE_HEADER}}
+
+namespace Icinga\Module\Doc;
+
+use Countable;
+use RecursiveFilterIterator;
+use Icinga\Data\Tree\NodeInterface;
+
+/**
+ * Recursive iterator over sections that are part of a particular chapter
+ */
+class SectionFilterIterator extends RecursiveFilterIterator implements Countable
+{
+    /**
+     * The chapter title to filter for
+     *
+     * @var string
+     */
+    protected $chapterTitle;
+
+    /**
+     * Create a new SectionFilterIterator
+     *
+     * @param NodeInterface $node           Node
+     * @param string        $chapterTitle   The chapter title to filter for
+     */
+    public function __construct(NodeInterface $node, $chapterTitle)
+    {
+        parent::__construct($node);
+        $this->chapterTitle = $chapterTitle;
+    }
+
+    /**
+     * Accept sections that are part of the given chapter
+     *
+     * @return bool Whether the current element of the iterator is acceptable
+     *              through this filter
+     */
+    public function accept()
+    {
+        $section = $this->getInnerIterator()->current()->getValue();
+        /* @var $section \Icinga\Module\Doc\Section */
+        if ($section->getChapterTitle() === $this->chapterTitle) {
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * (non-PHPDoc)
+     * @see RecursiveFilterIterator::getChildren()
+     */
+    public function getChildren()
+    {
+        return new static($this->getInnerIterator()->getChildren(), $this->chapterTitle);
+    }
+
+    /**
+     * (non-PHPDoc)
+     * @see Countable::count()
+     */
+    public function count()
+    {
+        return iterator_count($this);
+    }
+}