How would you design a ride-sharing system like Uber?

Services: rider app, driver app, matching service, pricing service, map/routing, payment. Real-time location: drivers send location updates, geospatial indexing (S2, Geohash), efficient radius queries. Matching: find nearby available drivers, ETA calculation, optimal assignment (Hungarian algorithm or greedy). Dispatch: WebSocket/push to driver, timeout and retry. Surge pricing: supply/demand per geohash cell. Data: trip history (time-series), driver locations (in-memory with persistence). Scale: city-based sharding, location service handles millions of updates. Consistency: ride state machine, idempotent state transitions.