The challenge
The shop owner runs the draw in front of customers, and in public two failures are unacceptable: the app freezing on a weak phone, or the contest disappearing when the phone is replaced.
What we built
Contests are kept in a local database with automatic backup when the phone changes, the draw was lightened to run on low-end phones, and the app size was cut.
Names arrive directly from WhatsApp instead of being typed under pressure, followed by shuffling names, a countdown and sound, because people trust a draw they can see happen.
Licensing and updates are serverless, and any update whose fingerprint does not match is rejected.
The outcome
A smooth draw in front of customers on any phone, with contests that are never lost.