Working offline
What happens when the device has no internet.
The free app never needs the internet.
The Pro licence offline
Pro is checked online. After each check Langouste keeps Pro features on for up to 7 days without the network. With internet, the check happens by itself.
If 7 days have passed
Pro features pause; everything free keeps working. Connect to the internet or restart Langouste and Pro comes back.
Turning the clock back doesn't extend the licence: Langouste remembers the latest time it has seen.