Repair open HTML tags in a PHP string

close_open_html_tags.php

<?php

/**
 * Find unclosed HTML tags in a string and repair them.
 * For example:
 *    $str = '<p>Hi, I\'m <b><a href="mailto:za ... ">Zack</a>';
 *    echo close_open_html_tags( $str );
 * would show '<p>Hi, I\'m <b><a href="mailto:za ... ">Zack</a></b></p>'
 */
function close_open_html_tags( $str ) {

	// Find all open tags
	preg_match_all( '@<(?P<elem>[a-z]+)[ |>]@Ui', $str, $open_tags );
	preg_match_all( '@</(?P<elem>[a-z]+)[ |>]@Ui', $str, $close_tags );
	$open_tags = $open_tags['elem'];
	$close_tags = $close_tags['elem'];
	
	// Work our way out in the order they would be closed
	$open_tags = array_reverse( $open_tags );
	for( $i=0; $i<count($close_tags); $i++ ) {
		if( $open_tags[$i] == $close_tags[$i] ) {
			// This tag was closed and in the proper order
			unset( $open_tags[$i] );
		}
	}
	
	// Close all open tags
	foreach( $open_tags as $open_tag ) {
		$str .= "</$open_tag>";
	}
	
	return $str;
}