Build a cab booking system like Uber

• Riders and drivers register; drivers have a location, a cab type (mini, sedan, SUV) and a status (offline, available, on trip); updateLocation(driverId, lat, lng) keeps positions current
• requestRide(riderId, pickup, drop, cabType) finds available drivers of that type within a radius and assigns the nearest through a matching strategy; no driver means a clear "no cabs" result
• A trip follows a lifecycle: requested, driver assigned, driver arrived, in progress, completed or cancelled; invalid transitions are rejected and the driver is freed on completion or cancellation
• A driver can decline; the request then goes to the next nearest driver, skipping those already asked, until one accepts or candidates run out
• A fare strategy computes the price from distance, duration, cab type and a surge multiplier (injectable), and the fare is calculated when the trip completes
• After completion, the rider and driver can rate each other from 1 to 5; driver rating is the running average, and two concurrent requests never get the same driver

Only after every requirement works.

• Spatial index (grid or geohash) for nearby-driver lookup
• Ride pooling for two riders
• Cancellation fees and driver timeouts for unanswered requests