Have you looked into using MessagesKit.framework? (In /System/Library/PrivateFrameworks) If it's written in Obj-C, you can extract fully usable headers from it

Have you looked into using MessagesKit.framework? (In /System/Library/PrivateFrameworks) If it's written in Obj-C, you can extract fully usable headers from it. If C++/C/etc., it will be difficult (but not impossible) to understand it. After extracting the headers from that, you may well be able to use it instead of AppleScript.