It will be useful to have a sensor which can change states based on transition or home assistant events
Currently, we do not have a simple way of achieving this as we need individual automations to trigger the transitions and use input_select to maintain the state and combine that with other entity states to do the necessary transitions.
Triggered template sensors have been a thing for a while now.
This will still need triggers to account for the initial states:
For Example:
Awake - > On Bed + Night → Going to Bed
Going to Bed → Phone charger connected → Sleeping
Sleeping → In Bed + Phone Charger Disconnected → Waking up
Waking up → Off Bed + Morning → Awake
Yes, all that can be templated in the trigger and/or state.