write-viewmodel

# Write ViewModel ## Overview ViewModels in Alkaa bridge domain use cases and Compose UI via cold flows and sealed state classes. They contain no business logic — only orchestration, mapping, and scope management. ## Structure 1. **Sealed State Class** — `data object` for stateless states, `data class` for states with data, `ImmutableList` for list payloads → see `references/CODE_PATTERNS.md` 2. **Flow Exposure** — Cold `Flow<ViewState>` by default; hot `StateFlow` only when multiple collectors share the same stream → see `references/CODE_PATTERNS.md` 3. **Use Case Injection** — Inject use cases as constructor parameters; never repositories or other ViewModels → see `references/CODE_PATTERNS.md` 4. **Coroutine Scope** — `applicationScope` for DB mutations that survive ViewModel destruction; `viewModelScope` for UI-bound work → see `references/CODE_PATTERNS.md` 5. **Mappers** — Dedicated mapper class injected as constructor param; never map inline → see `references/CODE_PATTERNS.md` For unit test setup and fake patterns → see `references/CODE_PATTERNS.md` and the `write-unit-tests` skill. ## Scope Rules | Situation | Scope | |-----------|-------| | DB insert / update / delete | `applicationScope.launch { }` | | Network call that should persist | `applicationScope.launch { }` | | Debounced UI updates | `viewModelScope` | | Short-lived UI-bound work | `viewModelScope` | ## Common Mistakes | Mistake | Fix | |---------|-----| | Calling repository directly | Wrap in a use case first | | Exposing `StateFlow` for a screen-scoped stream | Return cold `Flow<ViewState>` | | Mapping models inline in ViewModel | Create a `XxxMapper` class | | Using `viewModelScope` for DB writes | Use `applicationScope.launch { }` | | Depending on another ViewModel | Extract shared logic into a use case | | Testing with mocks | Write a `XxxFake` that implements the use case interface | ## Related Skills - **Fake patterns and test structure** → use `write-unit-tests` skill - **Composable and screen wiring** → use `write-composable` skill