Convert BBCode-generated HTML back to BBCode

I have this function to parse bbcode -> html:

$this->text = preg_replace(array(
    '/\[b\](.*?)\[\/b\]/ms', 
    '/\[i\](.*?)\[\/i\]/ms',
    '/\[u\](.*?)\[\/u\]/ms',
    '/\[img\](.*?)\[\/img\]/ms',
    '/\[email\](.*?)\[\/email\]/ms',
    '/\[url\="?(.*?)"?\](.*?)\[\/url\]/ms',
    '/\[size\="?(.*?)"?\](.*?)\[\/size\]/ms',
    '/\[youtube\](.*?)\[\/youtube\]/ms',
    '/\[color\="?(.*?)"?\](.*?)\[\/color\]/ms',    
    '/\[quote](.*?)\[\/quote\]/ms',
    '/\[list\=(.*?)\](.*?)\[\/list\]/ms',
    '/\[list\](.*?)\[\/list\]/ms',
    '/\[\*\]\s?(.*?)\n/ms'
   ),array(
    '<strong>\1</strong>',
    '<em>\1</em>',
    '<u>\1</u>',
    '<img src="\1" alt="\1" />',
    '<a href="mailto:\1">\1</a>',
    '<a href="\1">\2</a>',
    '<span style="font-size:\1%">\2</span>',
    '<object width="450" height="350"><param name="movie" value="\1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="\1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="450" height="350"></embed></object>',
    '<span style="color:\1">\2</span>',
    '<blockquote>\1</blockquote>',
    '<ol start="\1">\2</ol>',
    '<ul>\1</ul>',
    '<li>\1</li>'
   ),
   $original
);

Problem is, how to unparse this, like html -> bbcode?

Don't.

Instead, store both the original unparsed text and the processed parsed text. Yes, this doubles the storage requirement, but it also makes it blindingly easy to:

1. Allow user edits of the original without parsing the BBCode back out
2. Allow quotes of other user posts, again without parsing
3. Change the HTML each BBCode generates (just re-parse every post)
4. Switch BBCode engines down the line (again, just re-parse every post)