nl2br.php

/**
 * Automatically applies "p" and "br" markup to text.
 * Basically [nl2br](http://php.net/nl2br) on steroids.
 *
 *     echo Text::auto_p($text);
 *
 * [!!] This method is not foolproof since it uses regex to parse HTML.
 *
 * @param   string  $str    subject
 * @param   boolean $br     convert single linebreaks to <br />
 * @return  string
 */
public static function auto_p($str, $br = TRUE)
{
    // Trim whitespace
    if (($str = trim($str)) === '')
        return '';

    // Standardize newlines
    $str = str_replace(array("\r\n", "\r"), "\n", $str);

    // Trim whitespace on each line
    $str = preg_replace('~^[ \t]+~m', '', $str);
    $str = preg_replace('~[ \t]+$~m', '', $str);

    // The following regexes only need to be executed if the string contains html
    if ($html_found = (strpos($str, '<') !== FALSE))
    {
        // Elements that should not be surrounded by p tags
        $no_p = '(?:p|div|h[1-6r]|ul|ol|li|blockquote|d[dlt]|pre|t[dhr]|t(?:able|body|foot|head)|c(?:aption|olgroup)|form|s(?:elect|tyle)|a(?:ddress|rea)|ma(?:p|th))';

        // Put at least two linebreaks before and after $no_p elements
        $str = preg_replace('~^<'.$no_p.'[^>]*+>~im', "\n$0", $str);
        $str = preg_replace('~</'.$no_p.'\s*+>$~im', "$0\n", $str);
    }

    // Do the <p> magic!
    $str = '<p>'.trim($str).'</p>';
    $str = preg_replace('~\n{2,}~', "</p>\n\n<p>", $str);

    // The following regexes only need to be executed if the string contains html
    if ($html_found !== FALSE)
    {
        // Remove p tags around $no_p elements
        $str = preg_replace('~<p>(?=</?'.$no_p.'[^>]*+>)~i', '', $str);
        $str = preg_replace('~(</?'.$no_p.'[^>]*+>)</p>~i', '$1', $str);
    }

    // Convert single linebreaks to <br />
    if ($br === TRUE)
    {
        $str = preg_replace('~(?<!\n)\n(?!\n)~', "<br />\n", $str);
    }

    return $str;
}