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A booking system that cannot double-book
Calendars, time zones and the concurrency bug that ruins them.
Why it matters
Double-booking is a concurrency bug with a business consequence, which makes it a perfect interview story. Time zones are the other half nobody plans for.
What you build
- Availability computed from rules, not stored slots
- Bookings that cannot overlap, under concurrency
- Correct behaviour across time zones and DST
- A test that fires two bookings at once
If you want more
- Add recurring availability
- Add calendar sync
Build it
- Compute availability from rules rather than storing every slot
- Handle cancellation and release the slot
- Fire two concurrent bookings for the same slot and assert one fails
Material for the whole build
Shows you can reason about concurrency and about time, two things that quietly break most applications.
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