Insert div between specific elements - php

Question

I have previously built some html pages where several paragraphs are inside div and now i want to move it in WordPress to understand theming and the structure of the CMS but i have some issues to understand. For example, in the loop i can't just add the opening div at the starting point and the closing div at the end (obviously) because in the middle there are different elements wrapped in other div. For example, I wanted to take the last paragraph, create a wrapping div around it with a custom class and my solution was this. I am sure it is a totally messed up solution. What am I doing wrong?
// First function
function addDivLastP1( $content ) {
$pattern = '/[\s\S]*\K(<p>)/i';
// Here i adding the opening tag div. I close it later in another function
$replacement = '<div class="my_class">$1';
$content = preg_replace( $pattern, $replacement, $content );
return $content;
}
add_filter( 'the_content', 'addDivLastP1' );
// Second function
function addDivLastP2( $content ) {
$pattern = '/[\s\S]*\K(<\/p>)/i';
// Closing div previously open
$replacement = '</div>';
$content = preg_replace( $pattern, $replacement, $content );
return $content;
}
add_filter( 'the_content', 'addDivLastP2' );

Answer 1

It is not a good idea to parse HTML (or any XML) by regexp.
In your case much better use DOMDocument:
function addDivLastP( $content ) {
$doc = new DOMDocument();
if(!$doc->loadHTML($content)) {
// cannot parse HTML content
return $content;
}
for($i = $doc->childNodes->count()-1; $i >= 0; $i--) {
$child = $doc->childNodes[$i];
if ($child->nodeName === 'p') { // got last paragraph inside root node
$div = $doc->createElement('div');
// replace paragraph by new empty div
$doc->replaceChild($div, $child);
// insert paragraph inside div
$div->appendChild($child);
return $doc->saveHTML();
}
}
return $content;
}