Laravel beginner, common function in controller (polymorphism)

I have a project, booking facility of hotel rooms, when I'm coding i got a doubt.. Using a controller to manage bookings.. I need a function that wich to check empty rooms available or not (free room).. If free room available then permit to book the room.. I've to check it when

• displaying rooms
• dispalying room
• while booking
• and also while paying...

where do i write the code.. In bookingController or in middleware or any other places...?

via Chebli Mohamed