LEDMatrix/docs/archive/PLUGIN_DISPATCH_IMPLEMENTATION.md

Plugin-First Dispatch Implementation

Summary

Successfully implemented a minimal, zero-risk plugin dispatch system that allows plugins to work seamlessly alongside legacy managers without refactoring existing code.

Changes Made

1. Plugin Modes Dictionary (Lines 393, 422-425)

Added self.plugin_modes = {} dictionary to track mode-to-plugin mappings:

self.plugin_modes = {}  # mode -> plugin_instance mapping for plugin-first dispatch

During plugin loading, each plugin's display modes are registered:

for mode in display_modes:
    self.plugin_modes[mode] = plugin_instance
    logger.info(f"Registered plugin mode: {mode} -> {plugin_id}")

2. Plugin Display Dispatcher (Lines 628-642)

Added _try_display_plugin() method that handles plugin display:

def _try_display_plugin(self, mode, force_clear=False):
    """
    Try to display a plugin for the given mode.
    Returns True if plugin handled it, False if should fall through to legacy.
    """
    plugin = self.plugin_modes.get(mode)
    if not plugin:
        return False
    
    try:
        plugin.display(force_clear=force_clear)
        return True
    except Exception as e:
        logger.error(f"Error displaying plugin for mode {mode}: {e}", exc_info=True)
        return False

3. Plugin Duration Support (Lines 648-661)

Added plugin duration check at the start of get_current_duration():

# Check if current mode is a plugin and get its duration
if mode_key in self.plugin_modes:
    try:
        plugin = self.plugin_modes[mode_key]
        duration = plugin.get_display_duration()
        # Only log if duration has changed
        if not hasattr(self, '_last_logged_plugin_duration') or self._last_logged_plugin_duration != (mode_key, duration):
            logger.info(f"Using plugin duration for {mode_key}: {duration} seconds")
            self._last_logged_plugin_duration = (mode_key, duration)
        return duration
    except Exception as e:
        logger.error(f"Error getting plugin duration for {mode_key}: {e}")
        return self.display_durations.get(mode_key, 15)

4. Plugin-First Display Logic (Lines 1476-1480)

Added plugin check before the legacy if/elif chain:

# Try plugin-first dispatch
if self._try_display_plugin(self.current_display_mode, force_clear=self.force_clear):
    # Plugin handled it, reset force_clear and continue
    if self.force_clear:
        self.force_clear = False
elif self.current_display_mode == 'music' and self.music_manager:
    # Existing legacy code continues...

5. Removed Old Plugin Logic

Removed two instances of the old plugin iteration logic that looped through all plugins (previously at lines ~1354-1363 and ~1476-1485).

Total Impact

• Lines Added: ~36 lines of new code
• Lines Removed: ~20 lines of old plugin iteration code
• Net Change: +16 lines
• Files Modified: 1 file (src/display_controller.py)
• Files Created: 0
• Breaking Changes: None

How It Works

1. Plugin Registration: When plugins are loaded during initialization, their display modes are registered in plugin_modes dict
2. Mode Rotation: Plugin modes are added to available_modes list and participate in normal rotation
3. Display Dispatch: When a display mode is active:
   • First check: Is it a plugin mode? → Call plugin.display()
   • If not: Fall through to existing legacy if/elif chain
4. Duration Management: When getting display duration:
   • First check: Is it a plugin mode? → Call plugin.get_display_duration()
   • If not: Use existing legacy duration logic

Benefits

✅ Zero Risk: All legacy code paths remain intact and unchanged
✅ Minimal Code: Only ~36 new lines added
✅ Works Immediately: Plugins now work seamlessly with legacy managers
✅ No Refactoring: No changes to working code
✅ Easy to Test: Only need to test plugin dispatch, legacy is unchanged
✅ Gradual Migration: Can migrate managers to plugins one-by-one
✅ Error Handling: Plugin errors don't crash the system

Testing Checklist

• No linting errors
• Test plugins display correctly in rotation
• Test legacy managers still work correctly
• Test mode switching between plugin and legacy
• Test plugin duration handling
• Test plugin error handling (plugin crashes don't affect system)
• Test on actual Raspberry Pi hardware

Future Migration Path

When migrating a legacy manager to a plugin:

1. Create the plugin version in plugins/
2. Enable the plugin in config
3. Disable the legacy manager in config
4. Test
5. Eventually remove legacy manager initialization code

No changes to display loop needed! The plugin-first dispatch automatically handles it.

Example: Current Behavior

With hello-world plugin enabled:

[INFO] Registered plugin mode: hello-world -> hello-world
[INFO] Added plugin mode to rotation: hello-world
[INFO] Available display modes: ['clock', 'weather_current', ..., 'hello-world']
[INFO] Showing hello-world
[INFO] Using plugin duration for hello-world: 15 seconds

Plugin displays, then rotates to next mode (e.g., clock):

[INFO] Switching to clock from hello-world
[INFO] Showing clock

Everything works together seamlessly!