---
phase: 07-chat-infrastructure
plan: 03
status: complete
type: tdd
started: 2026-01-27
completed: 2026-01-27
---

# Phase 7 Plan 3: WebSocket Integration & Selectors Summary

**Implemented WebSocket message handling and memoized selectors using TDD methodology**

## Accomplishments

- Added CHAT_MESSAGE handler to useSessionWebSocket.js with message transformation and unread increment logic
- Implemented 8 memoized selectors using Reselect (createSelector from Redux Toolkit)
- Created localStorage utilities (saveLastReadAt, loadLastReadAt, clearLastReadAt) for lastReadAt persistence
- Comprehensive unit test suite with 90 tests (14 WebSocket, 68 Redux/selectors, 8 localStorage)
- WebSocket message routing validated (Protocol Buffer → Redux format transformation)
- Selector memoization performance confirmed (same reference for unchanged state)
- localStorage error handling validated (quota exceeded, JSON parse errors)

## Files Created/Modified

### Created Files
- `jam-ui/src/hooks/__tests__/useSessionWebSocket.test.js` - WebSocket handler tests (14 tests)
- `jam-ui/src/helpers/chatStorage.js` - localStorage utilities for lastReadAt persistence
- `jam-ui/src/helpers/__tests__/chatStorage.test.js` - localStorage utility tests (8 tests)

### Modified Files
- `jam-ui/src/hooks/useSessionWebSocket.js` - Added CHAT_MESSAGE handler with message transformation and unread logic
- `jam-ui/src/store/features/sessionChatSlice.js` - Added 8 memoized selectors and localStorage integration
- `jam-ui/src/store/features/__tests__/sessionChatSlice.test.js` - Added 15 selector tests (total 68 tests)

## Decisions Made

**Channel Key Construction:**
- Session messages: Use `session_id` directly as channel key
- Lesson messages: Use `lesson_session_id` directly as channel key
- Global messages: Use literal string `'global'` as channel key
- Extracted `getChannelKeyFromMessage()` helper function for consistency across WebSocket and Redux

**Unread Increment Logic:**
- Increment unread count if chat window is closed (regardless of active channel)
- Increment unread count if window is open but viewing a different channel
- Do NOT increment if window is open and viewing the same channel
- Uses `useSelector` in WebSocket hook to access real-time chat state

**localStorage Error Strategy:**
- All functions catch errors without throwing (graceful degradation)
- Quota exceeded errors: Data not saved, but app continues normally
- JSON parse errors: Return empty object `{}` to allow app initialization
- Console.error for debugging, but no user-facing errors

**Selector Memoization:**
- Used `createSelector` from Redux Toolkit (includes Reselect)
- Input selectors are private (direct state access)
- Output selectors are exported for component use
- Selectors with parameters use second argument pattern: `(state, param) => param`

## Issues Encountered

None. TDD methodology helped catch issues early:
- Tests for message transformation caught snake_case → camelCase conversion needs
- Tests for unread logic clarified window state requirements
- Tests for localStorage validated error handling before integration

## Test Coverage

**Total Tests: 90** (all passing)
- WebSocket handler: 14 tests (message transformation, channel keys, unread logic, integration)
- Redux selectors: 15 tests (8 selectors with edge cases and memoization validation)
- Redux reducers/thunks: 53 tests (from previous plans, still passing)
- localStorage utilities: 8 tests (save, load, clear with error handling)

**TDD Phases Executed:**
- Task 1: RED (tests fail) → GREEN (implementation) → REFACTOR (JSDoc) - 3 commits
- Task 2: RED (tests fail) → GREEN (implementation) → REFACTOR (JSDoc) - 3 commits
- Task 3: RED (tests fail) → GREEN (implementation) → REFACTOR (docs) - 3 commits

## Next Phase Readiness

**Phase 7 complete!** Redux infrastructure (state, reducers, thunks, selectors, WebSocket integration, localStorage persistence) fully implemented and tested.

**Ready for Phase 8 (Chat Window UI & Message Display).**

Phase 8 will build the UI components:
- JKSessionChatButton with unread badge
- JKSessionChatWindow with WindowPortal
- Message list with auto-scroll
- Message display components
- Text input composer

Use `/gsd:plan-phase 8` to break down Phase 8 into executable plans.
