Is it possible to send Hangout messages to someone using Google Scripts.
If there is, can you post an example script that shows the sending of Hangout Messages.
Google Chat used to use XMPP which may have done but Hangouts uses its own proprietary protocol. https://www.eff.org/deeplinks/2013/05/google-abandons-open-standards-instant-messaging
There has recently been a 3rd party reverse engineering project for the protocol - a python library - which you could fork for GAS but like all such projects it is unsupported Google and therefore subject to any change in the protocol.