# Phase 2 Session Lifecycle Migration - Completed

## Summary

Successfully migrated session lifecycle state from `useState` hooks to Redux in **JKSessionScreen.js**. This includes session join/leave operations, user tracks, connection status, and guard validation.

## Changes Made

### 1. Updated Imports

Added Redux actions and selectors for active session management:

```javascript
import {
  fetchActiveSession,
  joinActiveSession,
  leaveActiveSession,
  setGuardsPassed,
  setUserTracks,
  setConnectionStatus,
  clearSession,
  selectActiveSession,
  selectJoinStatus,
  selectHasJoined,
  selectGuardsPassed,
  selectUserTracks,
  selectShowConnectionAlert,
  selectSessionId
} from '../../store/features/activeSessionSlice';
```

### 2. State Migration

#### BEFORE (6 useState hooks for lifecycle):
```javascript
const [userTracks, setUserTracks] = useState([]);
const [showConnectionAlert, setShowConnectionAlert] = useState(false);
const [hasJoined, setHasJoined] = useState(false);
const [sessionGuardsPassed, setSessionGuardsPassed] = useState(false);
// Plus session data states...
```

#### AFTER (Redux selectors):
```javascript
// Redux session lifecycle state
const activeSession = useSelector(selectActiveSession);
const joinStatus = useSelector(selectJoinStatus);
const hasJoined = useSelector(selectHasJoined);
const sessionGuardsPassed = useSelector(selectGuardsPassed);
const userTracks = useSelector(selectUserTracks);
const showConnectionAlert = useSelector(selectShowConnectionAlert);
const reduxSessionId = useSelector(selectSessionId);
```

### 3. Session Fetch on Mount

Added effect to fetch active session data when component mounts:

```javascript
// Fetch session data when sessionId changes
useEffect(() => {
  if (sessionId && sessionId !== reduxSessionId) {
    console.log('Fetching active session:', sessionId);
    dispatch(fetchActiveSession(sessionId));
  }
}, [sessionId, reduxSessionId, dispatch]);
```

### 4. Guard Operations Updated

**Guard checks now dispatch Redux actions:**

```javascript
// In guardOnJoinSession function

// For CHILD role
dispatch(setUserTracks([]));

// After getting tracks from sessionModel
const tracks = await sessionModel.waitForSessionPageEnterDone();
dispatch(setUserTracks(tracks));

// After guards pass
dispatch(setGuardsPassed(true));
```

### 5. Join Session Updated

**Join operation now updates Redux state:**

```javascript
// In joinSession function, after successful join
const data = await response.json();

// Update Redux state - user has successfully joined
dispatch(joinActiveSession.fulfilled(data, '', { sessionId, options: {} }));
```

**Note:** The join logic remains in the component for now (hybrid approach) because it involves complex native client calls and message callback registrations. A future phase can refactor this to use the Redux thunk more fully.

### 6. Connection Status Monitoring

**Connection status changes now dispatch Redux actions:**

```javascript
// Monitor connection status changes
useEffect(() => {
  if (connectionStatus === ConnectionStatus.DISCONNECTED ||
    connectionStatus === ConnectionStatus.ERROR) {
    dispatch(setConnectionStatus('disconnected'));
  } else if (connectionStatus === ConnectionStatus.CONNECTED) {
    dispatch(setConnectionStatus('connected'));
  } else if (connectionStatus === ConnectionStatus.RECONNECTING) {
    dispatch(setConnectionStatus('reconnecting'));
  }
}, [connectionStatus, dispatch]);
```

### 7. Leave Session Updated

**Leave operation now clears Redux state:**

```javascript
const handleLeaveSubmit = async (feedbackData) => {
  try {
    // ... existing leave logic ...

    await sessionModel.handleLeaveSession();

    // Clear Redux session state
    dispatch(clearSession());

    dispatch(closeModal('leave'));
    history.push('/sessions');
  } catch (error) {
    // ... error handling ...
  }
};
```

### 8. Cleanup on Unmount

**Component unmount now clears Redux state:**

```javascript
useEffect(() => {
  return () => {
    unregisterMessageCallbacks();

    if (metronomeState.isOpen) {
      resetMetronome();
    }

    // Clear Redux session state on unmount
    dispatch(clearSession());
  };
}, [metronomeState.isOpen, resetMetronome, dispatch]);
```

## Benefits Achieved

1. **Centralized Session State**: All session lifecycle state in Redux
2. **Predictable State Flow**: Clear action → reducer → state flow
3. **Better Debugging**: Can inspect session state and lifecycle in Redux DevTools
4. **State Persistence**: Session state survives component re-renders
5. **Easier Testing**: Session logic testable via Redux actions
6. **Reduced Component Complexity**: Removed 6 useState hooks

## State Architecture

### Redux State Structure (activeSession):
```javascript
{
  sessionId: null,
  sessionData: null,
  joinStatus: 'idle', // 'idle' | 'joining' | 'joined' | 'leaving'
  guardsPassed: false,
  hasJoined: false,
  userTracks: [],
  connectionStatus: 'disconnected',
  showConnectionAlert: false,
  // ... other fields
}
```

### State Flow:

1. **Mount**:
   - `fetchActiveSession(sessionId)` → Fetches session data from API

2. **Guard Validation**:
   - User tracks retrieved → `dispatch(setUserTracks(tracks))`
   - Guards pass → `dispatch(setGuardsPassed(true))`

3. **Join Session**:
   - Guards passed + tracks ready → Join API called
   - Success → `dispatch(joinActiveSession.fulfilled(data))`
   - `hasJoined` becomes `true`

4. **Connection Monitoring**:
   - Connection changes → `dispatch(setConnectionStatus(status))`
   - Alert shown/hidden based on connection state

5. **Leave Session**:
   - User clicks Leave → Modal opens
   - User confirms → `sessionModel.handleLeaveSession()`
   - Redux state cleared → `dispatch(clearSession())`
   - Navigate to `/sessions`

6. **Unmount**:
   - Component unmounts → `dispatch(clearSession())`

## Non-Migrated State

The following state was **intentionally kept** as local useState:
- `requestingSessionRefresh` - Refresh request state
- `pendingSessionRefresh` - Pending refresh state
- `sessionRules` - Session rules (may migrate later)
- `subscriptionRules` - Subscription rules (may migrate later)
- `currentOrLastSession` - Local session cache (may migrate later)

These can be migrated in a future phase if needed.

## Lines of Code Impact

- **Removed**: ~12 lines of useState declarations
- **Added**: ~7 lines of Redux selectors + ~20 lines of dispatch calls
- **Net Addition**: ~15 lines (worth it for centralized state management)

## Testing Checklist

To verify Phase 2 migration:

### Session Lifecycle:
- [ ] Navigate to session screen with valid session ID
- [ ] Verify session data fetches from API
- [ ] Verify user tracks are retrieved during guards
- [ ] Verify guards pass and `sessionGuardsPassed` becomes true
- [ ] Verify session join succeeds and `hasJoined` becomes true
- [ ] Open Redux DevTools → Check `activeSession` state updates

### Connection Status:
- [ ] Disconnect from network
- [ ] Verify connection alert shows
- [ ] Verify Redux state: `connectionStatus: 'disconnected'`
- [ ] Reconnect to network
- [ ] Verify connection alert hides
- [ ] Verify Redux state: `connectionStatus: 'connected'`

### Leave Session:
- [ ] Click "Leave Session" button
- [ ] Confirm leave in modal
- [ ] Verify session leaves successfully
- [ ] Verify Redux state cleared (activeSession back to initial state)
- [ ] Verify navigation to `/sessions`

### Cleanup:
- [ ] Join a session
- [ ] Navigate away from session screen
- [ ] Verify Redux state cleared on unmount

### Redux DevTools:
- [ ] Watch state changes during session lifecycle
- [ ] Verify actions dispatched:
  - `activeSession/fetch/pending`
  - `activeSession/fetch/fulfilled`
  - `activeSession/setUserTracks`
  - `activeSession/setGuardsPassed`
  - `activeSession/join/fulfilled`
  - `activeSession/setConnectionStatus`
  - `activeSession/clearSession`

## Known Limitations

1. **Hybrid Join Approach**: The `joinSession` function still lives in the component with complex side effects (native client calls, callback registrations). A future refactor can move more of this logic to Redux middleware or sagas.

2. **Context Dependencies**: Still depends on `CurrentSessionContext` for `setCurrentSessionId` and `setCurrentSession`. These can be migrated in Phase 3.

3. **Session Model Integration**: Still uses `sessionModel` hook for some operations. Consider consolidating in future phases.

## Next Steps (Phase 3)

With lifecycle state successfully migrated, you can now proceed to:

1. **Phase 3**: Migrate entity collections to Redux:
   - Participants (`participants` array)
   - Jam Tracks (`selectedJamTrack`, `jamTrackStems`)
   - Backing Tracks
   - Recording state

2. **WebSocket Integration**: Use the `useSessionWebSocket` hook to integrate WebSocket callbacks with Redux actions automatically

3. **Context Cleanup**: Replace `CurrentSessionContext` with Redux selectors completely

## Files Modified

1. `src/components/client/JKSessionScreen.js` - Migrated session lifecycle state to Redux

## Rollback Instructions

If you need to rollback this change:
```bash
git checkout HEAD -- src/components/client/JKSessionScreen.js
```

This will restore the previous useState-based lifecycle management.

## Integration Points

### Current Session Context:
The component still uses `CurrentSessionContext` for:
- `setCurrentSessionId()` - Setting session ID in ref
- `setCurrentSession()` - Updating context session data
- `inSession()` - Checking if in session
- `currentSessionIdRef` - Ref to current session ID

**Future**: These can be replaced with Redux actions/selectors in Phase 3.

### Session Model Hook:
The component uses `useSessionModel` for:
- `waitForSessionPageEnterDone()` - Getting user tracks
- `handleLeaveSession()` - Leave operations
- `updateSessionInfo()` - Updating session info
- `trackChanges` - Handling WebSocket messages

**Future**: Consider consolidating session logic in Redux or creating a custom hook that wraps Redux.

## Performance Considerations

- **Memoized Selectors**: Redux selectors are automatically memoized by `useSelector`
- **Selective Re-renders**: Component only re-renders when selected state changes
- **No Prop Drilling**: Session state accessible anywhere via `useSelector`

## Debugging Tips

### Redux DevTools:

1. **View State Tree**: See entire `activeSession` state
2. **Action History**: Track all dispatched actions
3. **Time Travel**: Jump to any previous state
4. **State Diff**: See what changed between actions

### Console Logging:

Add logging to track state changes:
```javascript
useEffect(() => {
  console.log('Session lifecycle state:', {
    hasJoined,
    sessionGuardsPassed,
    userTracks: userTracks.length,
    connectionStatus: showConnectionAlert ? 'disconnected' : 'connected'
  });
}, [hasJoined, sessionGuardsPassed, userTracks, showConnectionAlert]);
```

## Migration Pattern Summary

This phase followed the pattern:

1. ✅ Import Redux actions/selectors
2. ✅ Replace useState with useSelector
3. ✅ Replace state setters with dispatch calls
4. ✅ Add fetch effect on mount
5. ✅ Update lifecycle operations (join/leave)
6. ✅ Add cleanup on unmount

This same pattern can be applied to Phase 3 for entity collections.
