"""Context engine plugin discovery.

Scans ``plugins/context_engine/<name>/`` for ``ContextEngine`` implementations. Engines live
in the repo (always available, no user install) and are separate from the general plugin
system. Only one is active (``context.engine`` in config.yaml; default ``"compressor"``,
the built-in ContextCompressor).
"""

from __future__ import annotations

import logging
from pathlib import Path
from typing import List, Optional, Tuple

from plugins import plugin_loader as _loader

logger = logging.getLogger(__name__)

_CONTEXT_ENGINE_PLUGINS_DIR = Path(__file__).parent


def discover_context_engines() -> List[Tuple[str, str, bool]]:
    """Return ``[(name, description, is_available), ...]`` for every bundled engine."""
    return [
        (
            child.name,
            _loader.read_plugin_description(child),
            _loader.probe_availability(lambda c=child: _load_engine_from_dir(c)),
        )
        for child in _loader.iter_plugin_dirs(_CONTEXT_ENGINE_PLUGINS_DIR)
    ]


def load_context_engine(name: str) -> Optional["ContextEngine"]:  # noqa: F821
    """Load a ContextEngine instance by name; None if not found or it fails to load."""
    engine_dir = _CONTEXT_ENGINE_PLUGINS_DIR / name
    if not engine_dir.is_dir():
        logger.debug("Context engine '%s' not found in %s", name, _CONTEXT_ENGINE_PLUGINS_DIR)
        return None
    return _loader.load_named(
        name, engine_dir, _load_engine_from_dir,
        kind="Context engine", noun="engine", logger=logger,
    )


def _load_engine_from_dir(engine_dir: Path) -> Optional["ContextEngine"]:  # noqa: F821
    """Import an engine module and extract its ContextEngine (register(ctx) or subclass)."""
    from agent.context_engine import ContextEngine

    name = engine_dir.name
    mod = _loader.load_plugin_module(
        f"plugins.context_engine.{name}", engine_dir,
        parents=("plugins", "plugins.context_engine"), logger=logger,
    )
    if mod is None:
        return None
    return _loader.instance_from_module(
        mod, collector=_EngineCollector(engine_name=name), collected_attr="engine",
        base_cls=ContextEngine, name=name, logger=logger,
    )


class _EngineCollector(_loader.NoopPluginContext):
    """Fake plugin context capturing register_context_engine; forwards register_command
    to the global plugin command registry so engine slash commands behave like plugin ones."""

    def __init__(self, engine_name: str = ""):
        self.engine = None
        self._engine_name = engine_name or "context_engine"
        self._registered_commands: list[str] = []

    def register_context_engine(self, engine):
        self.engine = engine

    def register_command(self, name: str, handler, description: str = "", args_hint: str = "") -> None:
        clean = (name or "").lower().strip().lstrip("/").replace(" ", "-")
        if not clean:
            logger.warning(
                "Context engine '%s' tried to register a command with an empty name.",
                self._engine_name,
            )
            return

        conflict = "Context engine '%s' tried to register command '/%s' which %s Skipping."
        try:
            from hermes_cli.commands import resolve_command
            if resolve_command(clean) is not None:
                logger.warning(conflict, self._engine_name, clean, "conflicts with a built-in command.")
                return
        except Exception:
            pass

        try:
            from hermes_cli.plugins import get_plugin_manager
            manager = get_plugin_manager()
            if clean in manager._plugin_commands:
                logger.warning(conflict, self._engine_name, clean, "is already registered by a plugin.")
                return
            manager._plugin_commands[clean] = {
                "handler": handler,
                "description": description or "Context engine command",
                "plugin": f"context-engine:{self._engine_name}",
                "args_hint": (args_hint or "").strip(),
            }
            self._registered_commands.append(clean)
            logger.debug("Context engine '%s' registered command: /%s", self._engine_name, clean)
        except Exception as exc:
            logger.debug(
                "Context engine '%s' could not register /%s: %s", self._engine_name, clean, exc,
            )