Moto Real-Time Bidding Simulation (Android)

This project is a native Android (Kotlin) simulation of Moto's real-time bidding and negotiation platform. It demonstrates proficiency in concurrency, WebSocket handling, clean architecture, and lifecycle management.

🏗 Architecture

The app adheres to Clean Architecture principles, utilising MVVM (Model-View-ViewModel) design pattern.

• Presentation Layer: Jetpack Compose (UI) + ViewModel (State Management).
• Domain Layer: Pure Kotlin models and Repository interfaces. Contains business logic isolated from the Android framework.
• Data Layer: Ktor Client for WebSockets, DTOs, and Repository implementation.

Timer Implementation (Lifecycle-Safe)

To ensure the timer remains accurate even when the app is backgrounded, or the process is paused by the OS (Doze mode), the timer does not count ticks. Instead, it calculates the targetTime (startTime + duration) and derives the UI progress using System.currentTimeMillis().

• Advantage: If the app is backgrounded for 5 seconds, upon resuming, the timer immediately reflects the correct remaining time without "freezing" or drifting.

WebSocket Handling

• Library: Ktor Client with OkHttp Engine.
• Resilience: The connection logic is wrapped in a while(isActive) coroutine loop.
• Reconnection: If the connection drops or the server is unreachable, the app catches the exception, delays for 3 seconds, and automatically attempts to reconnect.

State Flow

1. Server: Emits JSON events (NEGOTIATION or BID).
2. Repository: Maps DTOs to Domain Sealed Classes.
3. ViewModel:
   • Filters duplicate bids to prevent UI key crashes.
   • Sorts bids by amount (Ascending).
   • Updates the MutableStateFlow<AuctionState>.
4. UI: Consumes state via collectAsStateWithLifecycle to ensure UI updates stop when the Activity is stopped.

Known Limitations & Setup

• Backend: This app requires a local WebSocket server to function.
• Server Script: A Node.js mock server script (server.js) is included in the MockServer directory.
• Running:
  1. Ensure your phone/emulator and computer are on the same Wi-Fi.
  2. Update the IP address in KtorRealTimeService.kt to your local machine's IP.
  3. Run node server.js before launching the app.