How I generate index markers using Applescript and tagged text!

Question

One of the challenges I've faced in automating the book making process using Applescript with inDesign is that there don't seem to be any AS commands for making new index markers (anyone please correct me I if I'm wrong about this).
I've tried various js scripts which do an OK job, but they don't make the actual native markers. This means you have to wait until the book (consistiing of multiple ID files) is complete (so that all the page numbers have been established) to generate the index.
Recently, I read a tweet from someone with a link to a technique which uses tagged text and find and replace with GREP to edit the tags, inserting the tagged text index tags in the text file and then re-placing the text file in the ID page. In itself, this works great. But I'm dealing with literally thousands of separate text frames, none of them connected in a story.
The books typically consist of around 1200 pages with almost that many people, each of whose names I need to index with "Lastname, Firstname" references. And those particular strings don't (can't) appear anywhere on the pages. There will also be about 50 ID files all combined into one book. So it is imperative that I have ID generate the native index markers. To help keep things straight and efficient, I'm creating separate small text frames to hold the lastname, firstname strings. I created an object style for these frames which sets the attributes to "nonprinting", and I place the frames in the margin.
Then I realized that I don't actually have to have ID export the tagged text files for each. I exported one prototype and copied its tags to properties in my script, and then I concatenate them with the respective list item values I import from the database.
At the proper point in the page building script, I tell "textwrangleer" to make a new document, set its contents to the index string for the current record, save it to disk, overwriting the previous one, and then tell ID to "place" it in the index text frame, which generates the ID index mark.
I actually got an AS error when I first tried this: "file doesn't exist" or some such. Then I realized that the "place" command was happening too soon, so I inserted a .5 sec delay in the script, and it worked.
This is actually my first major script for actual work, and I'm so excited about it! I promises to cut production time down to about a thenth of what it was.
I still have to add some logic to branch between handlers with slightly different parameters for five different page formats, but the same page building handler will work on all of them.

Answer 1

A note on this:
Daniel Swanson wrote:
I've tried various js scripts which do an OK job, but they don't make the actual native markers. This means you have to wait until the book (consistiing of multiple ID files) is complete (so that all the page numbers have been established) to generate the index.
These scripts typically search for words and immediately write out the page numbers they are found on -- one shot indexing.
The solution is to add both the topic and its page reference to the current document's index:
if (app.activeDocument.indexes.length == 0)
    app.activeDocument.indexes.add();
app.activeDocument.indexes[0].topics.add(app.selection[0].contents).pageReferences.add(app.selection[0]);
The first lines only make sure there is an index to add to (per default, a new document has none).
The last line adds a selected word to the index (it must be a plain text string, hence the use of its 'contents'), and then adds a reference to the selection in the text itself.
Adding the same word a second time will for a change (quite untypically for ID's Scripting) not result in an error but simply add another page reference to the existing one.
When doing this in a loop: remember to work backwards, because the index marker itself gets inserted into the running text, and that will throw off your text indices.