"""Registry and factory for daily feature plugins."""

import importlib
import importlib.util
import inspect
from pathlib import Path
from typing import Optional, Type

from pipeline.features.base import BaseFeature

_REGISTRY: dict[str, Type[BaseFeature]] = {}
_builtins_loaded = False


def register_feature(cls: Type[BaseFeature]) -> Type[BaseFeature]:
    """Class decorator that registers a feature under ``BaseFeature.name``."""
    if not (isinstance(cls, type) and issubclass(cls, BaseFeature)):
        raise TypeError(f"{cls!r} is not a BaseFeature subclass")
    key = getattr(cls, "name", "")
    if not key:
        raise ValueError(f"{cls.__name__} must set a non-empty class attribute `name`")
    existing = _REGISTRY.get(key)
    if existing is not None and existing is not cls:
        raise ValueError(
            f"Feature name '{key}' already registered by {existing.__name__}"
        )
    _REGISTRY[key] = cls
    return cls


def available_features() -> list[str]:
    """Sorted names of all registered features (built-ins are loaded lazily)."""
    _ensure_builtins()
    return sorted(_REGISTRY)


def get_feature(name: str, **params) -> BaseFeature:
    """Instantiate a registered feature by name.

    Only parameters accepted by the feature class's ``__init__`` are forwarded.
    """
    _ensure_builtins()
    if name not in _REGISTRY:
        raise KeyError(f"Unknown feature '{name}'. Available: {sorted(_REGISTRY)}")
    cls = _REGISTRY[name]
    accepted = _accepted_params(cls)
    kwargs = params if accepted is None else {k: v for k, v in params.items() if k in accepted}
    return cls(**kwargs)


def load_feature_module(spec: str) -> None:
    """Import an external module so its ``@register_feature`` classes register."""
    looks_like_file = spec.endswith(".py") or Path(spec).expanduser().exists()
    if looks_like_file:
        path = Path(spec).expanduser().resolve()
        if not path.exists():
            raise FileNotFoundError(f"Feature module not found: {path}")
        module_spec = importlib.util.spec_from_file_location(path.stem, path)
        if module_spec is None or module_spec.loader is None:
            raise ImportError(f"Cannot load feature module from {path}")
        module = importlib.util.module_from_spec(module_spec)
        module_spec.loader.exec_module(module)
    else:
        importlib.import_module(spec)


def _accepted_params(cls: Type[BaseFeature]) -> Optional[set[str]]:
    """Param names ``cls.__init__`` accepts, or None if it takes ``**kwargs``."""
    sig = inspect.signature(cls.__init__)
    if any(p.kind is p.VAR_KEYWORD for p in sig.parameters.values()):
        return None
    return {name for name in sig.parameters if name != "self"}


def _ensure_builtins() -> None:
    global _builtins_loaded
    if not _builtins_loaded:
        import pipeline.features.library  # noqa: F401
        _builtins_loaded = True