'How to send whatsapp message from another android app? (see detail though)

I have an app and we want the following

Type message in this app(not whatsapp)
Our app knows the user from the contact list
Click send
Message should be sent to the user without whatsapp asking for the user except maybe in special case of multiple phone numbers maybe?
Message sent should show up in whatsapp history as part of the chat with the targetted user

Is this even possible? The post I read makes the user go into whatsapp and select the user to send the message to. Is that unavoidable?

android iphone whatsapp

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