"""Registry mapping ``(component type, backend)`` to implementation classes."""

from collections.abc import Iterator
from contextlib import contextmanager
from threading import RLock
from typing import Callable, TypeVar, cast

from .base_component import ComponentMixin
from ..enumeration import ComponentType, component_type_name

T = TypeVar("T", bound=ComponentMixin)


class ComponentRegistry:
    """Two-level registry: ``component_type -> name -> class``.

    Supports both direct calls — ``R.register(MyClass, "name")`` — and
    decorator usage — ``@R.register("name")``.
    """

    def __init__(self) -> None:
        self._registry: dict[str, dict[str, type[ComponentMixin]]] = {}
        self._owners: dict[tuple[str, str], str] = {}
        self._lock = RLock()
        self._frozen = False

    def _ensure_mutable(self) -> None:
        """Reject changes after this registry becomes an immutable template."""
        if self._frozen:
            raise RuntimeError("Component registry is frozen")

    def _do_register(self, cls: type[T], name: str, *, owner: str | None = None) -> type[T]:
        """Insert ``cls`` under its component type and reject ambiguous providers."""
        try:
            component_type = component_type_name(getattr(cls, "component_type", None))
        except (TypeError, ValueError) as exc:
            raise TypeError(f"{cls.__name__} must have a non-empty string 'component_type' attribute") from exc
        if not name:
            raise ValueError("Component name cannot be empty")

        with self._lock:
            self._ensure_mutable()
            group = self._registry.setdefault(component_type, {})
            key = (component_type, name)
            if name in group:
                existing = group[name]
                existing_owner = self._owners[key]
                new_owner = owner or cls.__module__
                if existing is cls and existing_owner == new_owner:
                    return cls
                raise ValueError(
                    f"Backend '{component_type}:{name}' is provided by both " f"'{existing_owner}' and '{new_owner}'",
                )
            group[name] = cls
            self._owners[key] = owner or cls.__module__
        return cls

    def add(self, name: str, cls: type[T], *, owner: str) -> type[T]:
        """Register one explicitly owned plugin contribution."""
        return self._do_register(cls, name, owner=owner)

    def register(
        self,
        cls_or_name: type[T] | str,
        name: str | None = None,
    ) -> Callable[[type[T]], type[T]] | type[T]:
        """Register a component class directly, or return a decorator that does so."""
        # Direct call: register(MyClass) or register(MyClass, "alias").
        if isinstance(cls_or_name, type):
            cls = cast(type[T], cls_or_name)
            return self._do_register(cls, name if name is not None else cls.__name__)

        # Decorator call: @R.register("alias") — must receive a string name.
        if not isinstance(cls_or_name, str):
            raise TypeError(f"Expected a class or string, got {type(cls_or_name).__name__}")

        registration_name = cls_or_name

        def decorator(decorated_cls: type[T]) -> type[T]:
            return self._do_register(decorated_cls, registration_name)

        return decorator

    def get(self, component_type: ComponentType, name: str) -> type[ComponentMixin] | None:
        """Look up a registered class; return None if not found."""
        with self._lock:
            return self._registry.get(component_type_name(component_type), {}).get(name)

    def get_all(self, component_type: ComponentType) -> dict[str, type[ComponentMixin]]:
        """Return a shallow copy of all classes registered under `component_type`."""
        with self._lock:
            return dict(self._registry.get(component_type_name(component_type), {}))

    def unregister(self, component_type: ComponentType, name: str) -> bool:
        """Remove an entry; return True if it existed, False otherwise."""
        component_type = component_type_name(component_type)
        with self._lock:
            self._ensure_mutable()
            if (group := self._registry.get(component_type)) and name in group:
                del group[name]
                self._owners.pop((component_type, name), None)
                return True
            return False

    def clear(self) -> None:
        """Drop every registered entry."""
        with self._lock:
            self._ensure_mutable()
            self._registry.clear()
            self._owners.clear()

    def freeze(self) -> None:
        """Make this registry an immutable template for future copies."""
        with self._lock:
            self._frozen = True

    @property
    def frozen(self) -> bool:
        """Whether mutating operations are disabled."""
        with self._lock:
            return self._frozen

    def copy(self) -> "ComponentRegistry":
        """Return an independent registry containing the same providers."""
        copied = ComponentRegistry()
        with self._lock:
            for component_type, group in self._registry.items():
                for name, implementation in group.items():
                    copied.add(name, implementation, owner=self._owners[(component_type, name)])
        return copied

    @contextmanager
    def preserve(self, *, allow_mutation: bool = False) -> Iterator[None]:
        """Restore the registry after code that may register through import side effects."""
        with self._lock:
            registry = {component_type: dict(group) for component_type, group in self._registry.items()}
            owners = dict(self._owners)
            frozen = self._frozen
            if allow_mutation:
                self._frozen = False
            try:
                yield
            finally:
                self._registry = registry
                self._owners = owners
                self._frozen = frozen


# Import-time registry for built-in implementations. Runtime code should use
# ``create_application_registry`` rather than mutate this template.
R = ComponentRegistry()


def create_application_registry() -> ComponentRegistry:
    """Return a mutable registry initialized from the frozen built-in template."""
    return R.copy()