plugin_state.py

"""
Plugin State Management

The display process's plugin state machine (loaded → enabled → running →
error), with state transitions and queries. It is the only record of plugin
lifecycle state: the web process runs no plugins, and reads this state as the
snapshot ``plugin_runtime.PluginRuntimePublisher`` publishes from it.
"""

import threading
import time
from enum import Enum
from typing import Optional, Dict, Any
from datetime import datetime
import logging

from src.logging_config import get_logger


class PluginState(Enum):
    """Plugin state enumeration."""
    UNLOADED = "unloaded"  # Plugin not loaded
    LOADED = "loaded"  # load_plugin() in progress: set before the module is imported
    ENABLED = "enabled"  # Plugin instantiated and enabled
    RUNNING = "running"  # Plugin is currently executing
    ERROR = "error"  # Plugin encountered an error
    DISABLED = "disabled"  # Plugin is disabled in config


def published_state(state: PluginState) -> PluginState:
    """The state as readers outside the scheduler see it.

    RUNNING is the scheduler's claim on a plugin for one update() call: every
    update flips ENABLED -> RUNNING -> ENABLED. Published as is, that would be
    a change -- and a cache write to the SD card -- on every plugin update, and
    a reader would see a plugin blink between two states that mean the same
    thing to it (loaded and taking part). Readers get ENABLED for both.
    """
    return PluginState.ENABLED if state == PluginState.RUNNING else state


class PluginStateManager:
    """Manages plugin state transitions and queries.

    Owned by the display process's PluginManager. ``change_count`` moves
    whenever something a reader of the published snapshot would see changes
    (published state, error info, the loaded record) and stays put across the
    RUNNING/ENABLED flip of an ordinary update, so a publisher can tell
    "nothing new" without diffing.
    """
    
    def __init__(self, logger: Optional[logging.Logger] = None) -> None:
        """
        Initialize the plugin state manager.
        
        Args:
            logger: Optional logger instance
        """
        self.logger = logger or get_logger(__name__)
        self._lock = threading.RLock()
        self._states: Dict[str, PluginState] = {}
        # Lifetime transition totals, reported by get_state_info().
        self._state_transition_counts: Dict[str, int] = {}
        self._error_info: Dict[str, Dict[str, Any]] = {}
        self._last_update: Dict[str, datetime] = {}
        # What load_plugin() registered: {'version', 'loaded_at'} per plugin
        # whose instance is live. Cleared with the rest of its state on unload.
        self._loaded: Dict[str, Dict[str, Any]] = {}
        self._change_count = 0

    @property
    def change_count(self) -> int:
        """Moves on every change a published snapshot would show."""
        with self._lock:
            return self._change_count

    def _note_change(self) -> None:
        """Count a reader-visible change. Callers must already hold ``_lock``."""
        self._change_count += 1
    
    def _record_transition(self, plugin_id: str) -> None:
        """Count a state transition. Callers must already hold ``_lock``."""
        self._state_transition_counts[plugin_id] = (
            self._state_transition_counts.get(plugin_id, 0) + 1
        )

    def set_state(
        self,
        plugin_id: str,
        state: PluginState,
        error: Optional[Exception] = None
    ) -> None:
        """
        Set plugin state and record transition.

        Args:
            plugin_id: Plugin identifier
            state: New state
            error: Optional error if transitioning to ERROR state
        """
        with self._lock:
            known = plugin_id in self._states
            old_state = self._states.get(plugin_id, PluginState.UNLOADED)
            self._states[plugin_id] = state
            self._record_transition(plugin_id)
            if not known or published_state(old_state) != published_state(state):
                self._note_change()

            # Store error info if transitioning to ERROR state
            if state == PluginState.ERROR and error:
                self._error_info[plugin_id] = {
                    'error': str(error),
                    'error_type': type(error).__name__,
                    'timestamp': datetime.now()
                }
                self._note_change()
            elif state != PluginState.ERROR:
                # Clear error info when leaving ERROR state
                if self._error_info.pop(plugin_id, None) is not None:
                    self._note_change()

            self.logger.debug(
                "Plugin %s state transition: %s → %s",
                plugin_id,
                old_state.value,
                state.value
            )
    
    def get_state(self, plugin_id: str) -> PluginState:
        """
        Get current state of a plugin.
        
        Args:
            plugin_id: Plugin identifier
            
        Returns:
            Current plugin state
        """
        return self._states.get(plugin_id, PluginState.UNLOADED)
    
    def is_loaded(self, plugin_id: str) -> bool:
        """Check if plugin is loaded."""
        state = self.get_state(plugin_id)
        return state in [PluginState.LOADED, PluginState.ENABLED, PluginState.RUNNING]
    
    def is_enabled(self, plugin_id: str) -> bool:
        """Check if plugin is enabled."""
        state = self.get_state(plugin_id)
        return state == PluginState.ENABLED
    
    def is_running(self, plugin_id: str) -> bool:
        """Check if plugin is currently running."""
        state = self.get_state(plugin_id)
        return state == PluginState.RUNNING
    
    def is_error(self, plugin_id: str) -> bool:
        """Check if plugin is in error state."""
        state = self.get_state(plugin_id)
        return state == PluginState.ERROR
    
    def can_execute(self, plugin_id: str) -> bool:
        """Check if plugin can execute (update/display)."""
        state = self.get_state(plugin_id)
        return state == PluginState.ENABLED
    
    def set_state_with_error(
        self,
        plugin_id: str,
        state: PluginState,
        error_info: Dict[str, Any],
    ) -> None:
        """Set plugin state and persist error context atomically.

        Holds ``_lock`` for both writes so no reader can observe the new
        state without the accompanying error context.

        Intentionally does not clear ``_error_info`` the way set_state() does
        for non-ERROR transitions — this is the recoverable-failure path where
        the error dict is the entire point.

        Args:
            plugin_id: Plugin identifier
            state: New state
            error_info: Structured error dict to persist alongside the state
        """
        with self._lock:
            old_state = self._states.get(plugin_id, PluginState.UNLOADED)
            self._states[plugin_id] = state
            self._record_transition(plugin_id)
            self._error_info[plugin_id] = dict(error_info)
            self._note_change()

            self.logger.debug(
                "Plugin %s state transition: %s → %s (recoverable error stored)",
                plugin_id,
                old_state.value,
                state.value,
            )

    def get_error_info(self, plugin_id: str) -> Optional[Dict[str, Any]]:
        """
        Get error information for a plugin.

        Returns the stored error dict whether the plugin is in ERROR state or
        still ENABLED after a recoverable failure. Returns a shallow copy so
        callers cannot mutate the stored snapshot.

        Args:
            plugin_id: Plugin identifier

        Returns:
            Copy of the error information dict, or None
        """
        with self._lock:
            info = self._error_info.get(plugin_id)
            return dict(info) if info is not None else None
    
    def record_loaded(self, plugin_id: str, version: Optional[str],
                      loaded_at: Optional[float] = None) -> None:
        """Record that ``plugin_id``'s instance is live, and which version.

        Called by PluginManager.load_plugin() once the instance is registered;
        clear_state() (unload) forgets it. ``version`` is the manifest's at
        load time, which is what the display keeps running until it reloads
        the plugin -- the version on disk can move on after a store update.
        """
        with self._lock:
            self._loaded[plugin_id] = {
                'version': version,
                'loaded_at': time.time() if loaded_at is None else loaded_at,
            }
            self._note_change()

    def record_unloaded(self, plugin_id: str) -> None:
        """Forget the loaded record alone, keeping state and error info: for
        an unload that failed after the instance was already dropped."""
        with self._lock:
            if self._loaded.pop(plugin_id, None) is not None:
                self._note_change()

    def runtime_records(self) -> Dict[str, Dict[str, Any]]:
        """Every known plugin's reader-visible state, taken in one critical
        section so a concurrent load or unload is seen whole or not at all.

        Per plugin: ``state`` (published_state()'s value), ``loaded``,
        ``version`` and ``loaded_at`` (None unless loaded) and ``error_info``
        (a copy, or None).
        """
        with self._lock:
            records: Dict[str, Dict[str, Any]] = {}
            for plugin_id in set(self._states) | set(self._loaded):
                loaded = self._loaded.get(plugin_id)
                info = self._error_info.get(plugin_id)
                records[plugin_id] = {
                    'state': published_state(
                        self._states.get(plugin_id, PluginState.UNLOADED)).value,
                    'loaded': loaded is not None,
                    'version': loaded['version'] if loaded else None,
                    'loaded_at': loaded['loaded_at'] if loaded else None,
                    'error_info': dict(info) if info is not None else None,
                }
            return records

    def record_update(self, plugin_id: str) -> None:
        """Record that plugin update() was called."""
        self._last_update[plugin_id] = datetime.now()
    
    def get_last_update(self, plugin_id: str) -> Optional[datetime]:
        """Get timestamp of last update() call."""
        return self._last_update.get(plugin_id)

    def get_state_info(self, plugin_id: str) -> Dict[str, Any]:
        """
        Get comprehensive state information for a plugin.
        
        Args:
            plugin_id: Plugin identifier
            
        Returns:
            Dictionary with state information
        """
        # One snapshot, one critical section. Each field was read under its own
        # lock, so an unload running concurrently could be observed half-done:
        # 'state' read before clear_state() removed it and
        # 'state_history_count' read after, giving a caller a plugin that is
        # ENABLED with zero transitions. _lock is an RLock, so the helpers
        # below can still take it.
        with self._lock:
            state = self.get_state(plugin_id)
            info = {
                'state': state.value,
                'is_loaded': self.is_loaded(plugin_id),
                'is_enabled': self.is_enabled(plugin_id),
                'is_running': self.is_running(plugin_id),
                'is_error': self.is_error(plugin_id),
                'can_execute': self.can_execute(plugin_id),
                'last_update': self.get_last_update(plugin_id),
                'error_info': self.get_error_info(plugin_id),
                'state_history_count': self._state_transition_counts.get(plugin_id, 0)
            }
        return info
    
    def clear_state(self, plugin_id: str) -> None:
        """Clear all state information for a plugin.

        Held under ``_lock`` so the dicts are dropped as one unit: every
        other mutator takes the lock, and without it a concurrent set_state()
        could interleave and leave a plugin with a transition count but no
        state.
        """
        with self._lock:
            had = (plugin_id in self._states or plugin_id in self._loaded
                   or plugin_id in self._error_info)
            self._states.pop(plugin_id, None)
            self._state_transition_counts.pop(plugin_id, None)
            self._error_info.pop(plugin_id, None)
            self._last_update.pop(plugin_id, None)
            self._loaded.pop(plugin_id, None)
            if had:
                self._note_change()