"""Per-runtime plugin adaptor registry with hybrid resolution.

Resolution order for ``(plugin_name, runtime)``:

  1. Platform registry  → ``workspace-template/plugins_registry/<plugin>/<runtime>.py``
  2. Plugin-shipped     → ``<plugin_root>/adapters/<runtime>.py``
  3. Raw filesystem     → :class:`RawDropAdaptor` (warns, drops files only)

Path #1 wins so the platform can override or hot-fix a third-party adaptor
without forking the upstream plugin repo. Path #2 is the SDK contract: a
single GitHub repo ships its own adaptors and is installable on day one.
Path #3 is the escape hatch — power users can still bring unsupported
plugins onto a workspace, they just don't get tools wired up.

A registered adaptor module must expose either:
  - ``Adaptor`` class implementing :class:`PluginAdaptor`, OR
  - ``def get_adaptor(plugin_name, runtime) -> PluginAdaptor``
"""

from __future__ import annotations

import importlib.util
import logging
from pathlib import Path
from typing import Optional

from .protocol import InstallContext, InstallResult, PluginAdaptor
from .raw_drop import RawDropAdaptor

logger = logging.getLogger(__name__)

# Where the platform-curated registry lives. Resolved relative to this file
# so it works regardless of CWD or how workspace-template is installed.
_REGISTRY_ROOT = Path(__file__).parent

__all__ = [
    "InstallContext",
    "InstallResult",
    "PluginAdaptor",
    "RawDropAdaptor",
    "resolve",
    "AdaptorSource",
]


class AdaptorSource:
    REGISTRY = "registry"
    PLUGIN = "plugin"
    RAW_DROP = "raw_drop"


def _load_module_from_path(module_name: str, path: Path):
    """Import a Python file by absolute path. Returns the module or None on failure."""
    spec = importlib.util.spec_from_file_location(module_name, path)
    if spec is None or spec.loader is None:
        return None
    module = importlib.util.module_from_spec(spec)
    try:
        spec.loader.exec_module(module)
    except Exception as exc:
        logger.warning("Failed to load adaptor module %s: %s", path, exc)
        return None
    return module


def _instantiate(module, plugin_name: str, runtime: str) -> Optional[PluginAdaptor]:
    """Build a PluginAdaptor from an adaptor module.

    Two conventions are supported so plugin authors can pick whichever fits:
    a class named ``Adaptor`` (zero-arg constructor or ``(plugin_name, runtime)``),
    or a factory function ``get_adaptor(plugin_name, runtime)``.
    """
    factory = getattr(module, "get_adaptor", None)
    if callable(factory):
        try:
            return factory(plugin_name, runtime)
        except Exception as exc:
            logger.warning("get_adaptor() failed for %s/%s: %s", plugin_name, runtime, exc)
            return None

    cls = getattr(module, "Adaptor", None)
    if cls is None:
        return None
    try:
        try:
            return cls(plugin_name, runtime)
        except TypeError:
            return cls()
    except Exception as exc:
        logger.warning("Adaptor() construction failed for %s/%s: %s", plugin_name, runtime, exc)
        return None


def _resolve_registry(plugin_name: str, runtime: str) -> Optional[PluginAdaptor]:
    path = _REGISTRY_ROOT / plugin_name / f"{runtime}.py"
    if not path.is_file():
        return None
    module = _load_module_from_path(f"plugins_registry.{plugin_name}.{runtime}", path)
    if module is None:
        return None
    return _instantiate(module, plugin_name, runtime)


def _resolve_plugin_shipped(plugin_root: Path, plugin_name: str, runtime: str) -> Optional[PluginAdaptor]:
    path = plugin_root / "adapters" / f"{runtime}.py"
    if not path.is_file():
        return None
    module = _load_module_from_path(f"_plugin_adaptor.{plugin_name}.{runtime}", path)
    if module is None:
        return None
    return _instantiate(module, plugin_name, runtime)


def resolve(
    plugin_name: str,
    runtime: str,
    plugin_root: Path,
) -> tuple[PluginAdaptor, str]:
    """Resolve the adaptor for ``(plugin_name, runtime)``.

    Returns ``(adaptor, source)`` where ``source`` is one of
    :class:`AdaptorSource` (``"registry"``, ``"plugin"``, ``"raw_drop"``).
    Always returns an adaptor — the raw-drop fallback ensures plugin installs
    never hard-fail on missing adaptors; instead the warning is surfaced via
    :class:`InstallResult.warnings`.
    """
    adaptor = _resolve_registry(plugin_name, runtime)
    if adaptor is not None:
        return adaptor, AdaptorSource.REGISTRY

    adaptor = _resolve_plugin_shipped(plugin_root, plugin_name, runtime)
    if adaptor is not None:
        return adaptor, AdaptorSource.PLUGIN

    return RawDropAdaptor(plugin_name, runtime), AdaptorSource.RAW_DROP