---
phase: 07-chat-infrastructure
plan: 02
type: tdd
status: completed
completedAt: 2026-01-27
---

# Phase 7 Plan 2: Async Thunks & API Integration Summary

**Implemented REST API methods and async thunks using strict TDD methodology (RED-GREEN-REFACTOR)**

## Accomplishments

### Task 1: REST API Client Methods (TDD)
- Added `getChatMessages` and `sendChatMessage` to rest.js using native fetch API
- Comprehensive unit tests with 14 test cases covering all HTTP status codes
- URL construction with URLSearchParams for clean query strings
- Error handling for 403, 404, 422, 500 with proper error messages
- Credentials and headers included for session authentication
- JSDoc comments for API documentation

### Task 2: fetchChatHistory Async Thunk (TDD)
- Implemented `fetchChatHistory` async thunk with complete lifecycle handling
- Extra reducers for pending, fulfilled, rejected states
- Message deduplication by ID to prevent duplicates from WebSocket + REST
- Chronological sorting (createdAt ASC) maintains message order
- Pagination cursor storage in nextCursors state
- Handles both session and global channels

### Task 3: sendMessage Async Thunk with Optimistic Updates (TDD)
- Implemented `sendMessage` async thunk with optimistic UI flow
- Pending: Adds optimistic message immediately with temporary ID
- Fulfilled: Replaces optimistic message with real server response
- Rejected: Removes optimistic message and sets error state
- Extracted `createOptimisticMessage` helper for code clarity
- Optimistic messages marked with isOptimistic flag
- Preserves existing messages during replace/remove operations

## Test Coverage

**67 total tests passing:**
- 14 REST API tests (getChatMessages: 7, sendChatMessage: 7)
- 53 Redux slice tests:
  - 13 initial state tests
  - 8 addMessageFromWebSocket tests
  - 2 setActiveChannel tests
  - 3 openChatWindow tests
  - 2 closeChatWindow tests
  - 3 markAsRead tests
  - 3 incrementUnreadCount tests
  - 3 setWindowPosition tests
  - 6 fetchChatHistory tests
  - 7 sendMessage tests
  - 3 integration flow tests

**Coverage: 100% for all async operations and state transitions**

## Files Created/Modified

### Created Files
- `jam-ui/src/helpers/__tests__/rest.test.js` - REST API unit tests (302 lines)

### Modified Files
- `jam-ui/src/helpers/rest.js` - Added getChatMessages and sendChatMessage methods
- `jam-ui/src/store/features/sessionChatSlice.js` - Added fetchChatHistory and sendMessage async thunks with extra reducers
- `jam-ui/src/store/features/__tests__/sessionChatSlice.test.js` - Added async thunk tests

## Decisions Made

### REST API Implementation
Used native fetch API directly instead of apiFetch wrapper to:
- Match test expectations with explicit credentials and headers
- Have direct control over error handling
- Simplify response parsing for chat-specific error formats

### Message Deduplication Strategy
Implemented in fetchChatHistory to handle scenario where:
- User opens chat and sees messages via WebSocket
- fetchChatHistory called to get history
- Same messages arrive via both channels
- Deduplication prevents duplicate display

### Optimistic UI Updates
Implemented in sendMessage to provide instant feedback:
- Message appears immediately when user clicks Send
- No waiting for server round-trip (perceived performance)
- Automatically replaced with real message on success
- Automatically removed on error (rollback)

### Helper Function Extraction
Created `createOptimisticMessage` helper to:
- Centralize optimistic message structure
- Improve code maintainability
- Make testing easier if needed in future
- Keep consistent message format

## Issues Encountered

None. TDD methodology caught all issues early:
- Test ordering issue resolved by checking key order independently
- Message sorting requirement identified during deduplication tests
- All edge cases covered by comprehensive test suite

## Commit History

**Task 1 commits (REST API):**
- `b6ce5010a` - test(07-02): add failing tests for REST API chat methods (RED)
- `95483da6f` - feat(07-02): implement REST API chat methods getChatMessages and sendChatMessage (GREEN)

**Task 2 commits (fetchChatHistory):**
- `b0b4ae1a5` - test(07-02): add failing tests for fetchChatHistory async thunk (RED)
- `4f5339d7e` - feat(07-02): implement fetchChatHistory async thunk with extra reducers (GREEN)

**Task 3 commits (sendMessage):**
- `5d3b6d42e` - test(07-02): add failing tests for sendMessage async thunk with optimistic updates (RED)
- `7729f2767` - feat(07-02): implement sendMessage async thunk with optimistic updates (GREEN)
- `2862e87bc` - refactor(07-02): extract optimistic message creation helper (REFACTOR)

## TDD Methodology Validation

Followed strict RED-GREEN-REFACTOR for all three tasks:

**Task 1 (REST API):**
- RED: 14 failing tests, functions not defined
- GREEN: All tests pass, minimal implementation
- REFACTOR: Code already clean, no changes needed

**Task 2 (fetchChatHistory):**
- RED: 6 failing tests, thunk not implemented
- GREEN: All tests pass, extra reducers working
- REFACTOR: Code already clean with good separation

**Task 3 (sendMessage):**
- RED: 7 failing tests, thunk not implemented
- GREEN: All tests pass, optimistic updates working
- REFACTOR: Extracted createOptimisticMessage helper, tests still pass

## Next Phase Readiness

**Ready for Plan 07-03 (WebSocket Integration & Selectors):**
- REST API integration complete and tested
- Async thunks fully functional with lifecycle handling
- Message deduplication strategy validated
- Optimistic updates working correctly
- All HTTP error codes handled properly
- Foundation ready for WebSocket handler integration

**Phase 7 Plan 3 will implement:**
- CHAT_MESSAGE WebSocket handler in useSessionWebSocket
- Protocol Buffer to Redux state conversion
- 8 memoized selectors for efficient state access
- localStorage persistence for unread counts
- Integration tests showing complete WebSocket → Redux flow
