Android - Build a custom screen popup while a Call is incoming or outgoing -- 2

I need an App where a single screen should serve my all the purpose. This App needs to show a custom screen popup while a Call is incoming, outgoing or Ongoing on Android phone. This custom popup must cover the entire screen, when any call is incoming, outgoing or ongoing only. Call Receiving/Answering, Rejecting, dropping will be possible using this app only. If the User Presses Home, Back or any the system key - this screen must not be disappeared. This app should work on any android device without rooting. I need the source code and compiled app both.