Wanted: a modified version of PlaceMultipagePDF -- to impose

Question

SCRIPT TO IMPOSE AN INCOMING PDF
I need a script that uses a modified version of the sample script supplied with CS4 (called PlaceMultiPagePDF.jsx, or the Applescript equivalent). Instead of placing the pages sequentially:
1 –> 1
2 –> 2
3 –> 3...
the script would place the PDF pages in 2-Up Perfect Bound imposition order. The arrangement is outlined in the attached document. It would be very flexible to allow for any combination of signature lengths. As a simple example, for a 8-page booklet, the script would place the pages from the PDF in this order in InDesign:
1 –> 2
2 –> 3
3 –> 6
4 –> 7
5 –> 6
6 –> 5
7 –> 4
8 –> 1
I have written a Pidgin BASIC code that handles the page sequencing (see attached document), but I have to steer clear of actually scripting it -- my programming skills end at MS BASIC ca 1986 (which I still use occasionally on my 512k Fat Mac as I can't get anything out of modern BASIC). Why did they ever complicate things with Java and the like?
Anyway, I have manually stepped through my flowchart several times and haven't come across an error, so all that is required ("all" he says, in hope) is to interrupt the pages coming from the PDF, and instead of 1 -> 1, 2->2... the script steps in and says "Whoa there... you're not going to page 315, you're going to page 297. Would it be that simple? As simple as inserting a bit of renumbering code as per my flowchart?
I hope so.
If anyone is interested, please let me know.

Answer 1

Thanks for the script, Jongware, but it is not quite what I need.I think yours generates one huge saddle-stitch arrangement, whereas I want the ability to generate a group of smaller ones (effectively a variable-length perfect-bound arrangement), thus my listing of "numbers of sheets" in each signature as the input.
Someone has been kind enough to write an Applescript that does the job. I haven't fully tested it, but really, what is there to test? It seems to work for me. One problem: it can't handle InDesign page numbers other than plain numbers, but I can work around that if I need to. Imposition from InDesign here I come -- run the script, paste the output into Page Range of the Export dialog box, and stand back while the bytes fly.
If a script could be run from the open Export window (to allow setting up of the various options), this script (or a JS version) could be carried one step further, not that I'm wanting to at this stage. The start page and the various signature lengths could be entered; options set up in the Export window; then the script could:
1. Generate the imposed number sequence and place them into the Page Range field of the active document;
2. Export the PDF;
3. Call on PlaceMultipagePDF, set to automatically create a new InDesign document and place the PDF pages.
It would be a very flexible, simple way of obtaining variable-length, 2-Up imposition from InDesign.
SCRIPT TO IMPOSE VARIABLE-LENGTH 2-UP SIGNATURES
set start to 1 -- overwrite with your starting page number
set s to {8, 1, 0} -- overwrite with the number of pages in each signature; any number of signatures allowed; must have 0 at end to stop.
set n to 1
set begin to start
set _end to start - 1 + 4 * (item n of s)
set outputStr to ""
repeat
set a to _end
set b to begin
set c to begin + 1
set d to _end - 1
set halfway to (begin + _end) / 2
repeat while b < halfway
set outputStr to outputStr & a & ","
set outputStr to outputStr & b & ","
set outputStr to outputStr & c & ","
set outputStr to outputStr & d & ","
set a to a - 2
set b to b + 2
set c to c + 2
set d to d - 2
end repeat
set n to n + 1
if item n of s = 0 then exit repeat
set begin to _end + 1
set _end to _end + 4 * (item n of s)
end repeat
set the clipboard to outputStr
return outputStr