AppleScript does not work in app save window - applescript

Question

I have an AppleScript that works perfectly in finder. It creates a folder named with the days date and has a shortcut key connected to it.
But it does not work when in another app, in the save window. Can you please help.
Here is the code I have.
tell application "Finder"
try
if exists Finder window 1 then
set thisPath to (the target of the front window) as alias
else
set thisPath to (path to desktop)
end if
on error
return
end try
end tell
set x to my the_perfect_datestring()
if x is not "-ERROR" then
set fullPath to thisPath & x as text
tell application "Finder"
try
--activate
if not (exists fullPath) then
set y to make new folder at thisPath with properties {name:x}
end if
activate
end try
end tell
end if
on the_perfect_datestring()
try
set cd to (the current date)
set the_year to year of (cd) as number
set the_month to month of (cd) as number
set the_day to day of (cd) as number
if the_month < 10 then set the_month to "0" & the_month
if the_day < 10 then set the_day to "0" & the_day
return ((the_year & "-" & the_month & "-" & the_day) as string)
on error
return "-ERROR"
end try

Answer 1

You cannot access the settings in a Save dialog box with the Finder AppleScript terminology.
The only way with AppleScript is System Events and GUI scripting. The script syntax depends strongly on the particular UI.

Answer 2

To work with save dialogs in other applications, you would need to change your workflow a bit. The save dialog works with text (the file/folder name), so you can create a text service to paste in the desired string.
To create a service, start up the Automator application and select the Service (Quick Action) document - the workflow will have settings that determine what kind of input it will accept, for example:
Workflow receives current text in any application
Next, check the Output replaces selected text box - this will replace selected text with the output of your workflow.
Drag a Run AppleScript action into the workflow, and completely replace the default contents with a new Run handler and your date string handler, for example:
on run {input, parameters}
set x to the_perfect_datestring()
if x is not "-ERROR" then return x
end run
on the_perfect_datestring()
try
# do your filename stuff
tell (current date) as «class isot» as string
return text 1 thru 10
end tell -- or whatever
on error
return "-ERROR"
end try
end the_perfect_datestring
After you save the workflow, the service should be available any time you select some text (in the right-click context menu).
An equivalent to your original workflow with the Finder would then be to create a new folder, and use the service on the highlighted “untitled folder” name to change it.