Duplicate Firing of `active chat message received` handler - macos

Question

While Manu G E asked a similar question twice, neither got an adequate answer, and I'm hoping I'll have better luck.
I'm writing an AppleScript to execute a handler when Messages.app receives a message. The script is being saved to ~/Library/Application\ Scripts/com.apple.iChat and is set in the Messages preferences to be the AppleScript handler.
When Messages is the frontmost application and a message is received, the active chat message received handler is fired twice. This doesn't seem to be a problem when Messages is in the background (received messages then fire message received, and that handler only once). I know which handler is fired because the portion that deals with the handlers looks like this:
using terms from application "Messages"
on message received _msg from _sender for _chat with _text_desc
if DEBUG then display dialog "message received"
message_received(_sender)
end message received
on chat room message received _msg from _sender for _chat with _text_desc
if DEBUG then display dialog "chat room message received"
message_received(_sender)
end chat room message received
on active chat message received _msg from _sender for _chat with _text_desc
if DEBUG then display dialog "active chat message received"
message_received(_sender)
end active chat message received
-- More handlers below, mostly like the above or empty
end using terms from
I set a DEBUG property to true and can see which handler gets fired.
I've tried working around this by writing a temporary file (using the UUID of the _sender). The message_received handler checks for the existence of the file and is supposed to do nothing if it's present. But this hasn't worked, even with random delays. I tried extending the length of the random delays, but this brings up errors about the AppleScript running for more than 10 seconds, even when enclosing the code within a with timeout of block.
Regardless of Apple's apparent support for executing AppleScripts in response to Messages events, perhaps I should look at some other mechanism to support this request from the client. I'm open to ideas.

Answer 1

Somehow I managed to find a simple but (very) dirty hack that seems to work for me, but I can't say if it will work on any machine. So "active chat message received" seems to be called twice at the same time, but I noticed something like do shell script "php -r 'echo microtime() >> file.txt'" sometimes reveals slightly different values.
I also use a property as a flag and try to take advantage of that shell execution tiny interval by writing to a file:
echo 0 > ~/Documents/flag.txt
then:
property flag : 0
using terms from application "Messages"
#...
on active chat message received theMessage from theBuddy
set response to false
set the_script to "cat ~/Documents/flag.txt"
set flag to do shell script the_script
do shell script "echo 1 > ~/Documents/flag.txt"
if flag is "0" then
set response to true
else
do shell script "echo 0 > ~/Documents/flag.txt"
end if
if response then
#this should be executed only once
end if
end active chat message received
#...
end using terms from
And voilà. Again I cannot say if that solution works everytime, and explaining why it actually works in my case is way beyond my capabilities right now. Still, I hope it will be useful. Cheers