Indesign scripting create deeper structures by adding tags

Question

I first set out to do this with XSLT, then with PHP. Now i'll have to have a go at it with Indesign scripting (javascript probably)

My problem is that i have an indesign file without structure (nothing is tagged, but everything has a paragraph style)

Wat i have to do is 1) ad tags to paragraphs based on their styles 2) deepen the structure by adding parent-elements to the tags

An example:

This text:

Titel 1 (style = title1)
Titel 2 (style = title2)
    some text (style = text1)
    listitem 1 (style = listitem)
    listitem 2 (style = listitem)

Has to become (on export to XML)

<GR.SEQ level="1">
<TITLE>
    <TI>
        <HT>
            Titel 1
        </HT>
    </TI>
</TITLE>

    <GR.SEQ level="2">
        <TITLE>
            <TI>
               <HT>
                    Titel 2
                </HT>
            </TI>
        </TITLE>
        <P>
            some text
        </P>
        <LIST>
            <ITEM>
                <ITEM.CONT>
                    listitem 1
                 </ITEM.CONT>
            </ITEM>
            <ITEM>
                <ITEM.CONT>
                    listitem 2
                </ITEM.CONT>
            </ITEM>
        </LIST>
    </GR>
</GR>

Any help is appreciated! a code-example that does this would be marvelous but a push in the right direction is also very welcome.

I would be very pleased already when i could change this:

Titel 1

to this

<TITLE>
    <TI>
        <HT>
            Titel 1
        </HT>
    </TI>
</TITLE>