write-viewmodel

name	write-viewmodel
description	Use when writing a new ViewModel or modifying an existing one in the Alkaa project. Triggers on tasks like "add a ViewModel", "create VM for X screen", "implement state handling", or "connect use case to UI".

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