# Kanban Column Refresh Solution

## Problem
When adding or editing kanban columns, changes didn't appear until the application was restarted.

## Root Cause
SQLAlchemy was caching the query results, so subsequent page loads would serve stale column data from cache instead of fetching fresh data from the database.

## Solution Implemented

### 1. Cache Clearing
Added `db.session.expire_all()` after every column modification to clear the SQLAlchemy session cache:
- After creating a column
- After editing a column
- After deleting a column
- After toggling column active status
- After reordering columns

### 2. Page Auto-Reload
Modified the drag-and-drop reorder functionality to automatically reload the page after successful reordering, ensuring the new order is visible immediately.

### 3. Real-Time Notifications (SocketIO)
Added WebSocket notifications to inform users viewing kanban boards when columns are modified:
- Emits `kanban_columns_updated` event after any column change
- Connected kanban boards receive a notification with a "Refresh page" link
- Notification auto-dismisses after 10 seconds

## How It Works

### For Column Management Page
1. User creates/edits/deletes/reorders a column
2. Database is updated
3. SQLAlchemy cache is cleared with `db.session.expire_all()`
4. SocketIO broadcasts `kanban_columns_updated` event to all connected clients
5. Page redirects back to column list (GET request fetches fresh data)
6. For reordering: Page auto-reloads after 1 second to show new order

### For Kanban Board Pages
1. User is viewing a kanban board (e.g., `/tasks`)
2. Admin makes a column change in another tab/browser
3. SocketIO notifies the open kanban board
4. User sees an alert: "Kanban columns have been updated. Refresh page"
5. User clicks link to reload and see updated columns

## Technical Details

### Cache Expiration
```python
# After every column modification
db.session.expire_all()
```
This tells SQLAlchemy to mark all cached objects as "stale" so they'll be refetched on next access.

### SocketIO Integration
```python
# Notify all connected clients
socketio.emit('kanban_columns_updated', {
    'action': 'created',  # or 'updated', 'deleted', 'toggled', 'reordered'
    'column_key': key
})
```

### JavaScript Listener
```javascript
// In kanban board
socket.on('kanban_columns_updated', function(data) {
    // Show notification with refresh link
    // Auto-dismiss after 10 seconds
});
```

## Benefits

1. **Immediate Feedback**: Column management changes reflect instantly
2. **No Restart Required**: SQLAlchemy cache is cleared automatically
3. **Multi-User Aware**: Other users are notified when columns change
4. **Graceful Degradation**: Works even if SocketIO is disabled
5. **User-Friendly**: Clear notification with easy refresh option

## Testing

### Test Cache Clearing
1. Go to `/kanban/columns`
2. Create a new column (e.g., "Testing")
3. Go to `/tasks` - new column should appear immediately
4. No restart required!

### Test Real-Time Notifications
1. Open `/tasks` in Browser Tab 1
2. Open `/kanban/columns` in Browser Tab 2
3. Create/edit a column in Tab 2
4. Watch Tab 1 - notification appears within 1 second
5. Click "Refresh page" link to see changes

### Test Reordering
1. Go to `/kanban/columns`
2. Drag a column to new position
3. Page reloads automatically
4. New order is visible immediately

## Fallback Behavior

If SocketIO is not available:
- Cache clearing still works
- Manual page refresh shows changes
- No errors thrown (wrapped in try/except)

If JavaScript is disabled:
- Form submissions still work
- Page redirects show updated data
- No dynamic notifications (graceful degradation)

## Performance Impact

- **Minimal**: `expire_all()` is a lightweight operation
- **No Database Load**: Only clears in-memory cache
- **Efficient**: SocketIO uses WebSockets (low overhead)
- **Scalable**: Works with multiple gunicorn workers

## Future Enhancements

Possible improvements:
1. **AJAX Reload**: Reload just the kanban board div without full page refresh
2. **Optimistic UI**: Update UI immediately, sync with server in background
3. **Selective Expiration**: Only expire `KanbanColumn` queries, not all queries
4. **Caching Strategy**: Implement Redis cache with TTL for column data

## Monitoring

To verify cache clearing is working:
```python
# Add logging to routes
import logging
logger = logging.getLogger(__name__)

# After modifications
logger.info(f"Column modified, cache cleared. Total columns: {KanbanColumn.query.count()}")
```

To verify SocketIO events:
```javascript
// In browser console
socket.on('kanban_columns_updated', (data) => {
    console.log('Received update:', data);
});
```

## Troubleshooting

### Changes still require restart
1. Check if `expire_all()` calls are present in all routes
2. Verify no other caching layer (Redis, memcached)
3. Check if using multiple app instances (load balancer)

### SocketIO notifications not working
1. Verify SocketIO is installed: `pip show flask-socketio`
2. Check browser console for WebSocket errors
3. Verify SocketIO is initialized in `app/__init__.py`
4. Check firewall allows WebSocket connections

### Page reload too slow
1. Reduce reload delay in JavaScript (currently 1 second)
2. Use AJAX instead of full page reload
3. Implement optimistic UI updates

## Conclusion

The solution provides immediate feedback for kanban column changes without requiring application restarts. It balances simplicity (cache clearing) with user experience (real-time notifications) while maintaining backwards compatibility.

