"""Registry for selectors and allocators — pluggable extension points."""

_selectors = {}
_allocators = {}


class RegistryError(Exception):
    pass


class SelectorNotFoundError(RegistryError):
    pass


class AllocatorNotFoundError(RegistryError):
    pass


def register_selector(type_name):
    def decorator(cls):
        _selectors[type_name] = cls
        cls.type = type_name
        return cls
    return decorator


def get_selector(spec):
    if not spec or not isinstance(spec, dict):
        raise ValueError(f"Invalid selector spec: {spec!r}")
    type_name = spec.get("type")
    if type_name not in _selectors:
        raise SelectorNotFoundError(
            f"No selector registered for type {type_name!r}. "
            f"Available: {list(_selectors.keys())}"
        )
    return _selectors[type_name](spec)


def register_allocator(strategy_name):
    def decorator(cls):
        _allocators[strategy_name] = cls
        cls.strategy = strategy_name
        return cls
    return decorator


def get_allocator(spec):
    if not spec or not isinstance(spec, dict):
        raise ValueError(f"Invalid allocation spec: {spec!r}")
    strategy = spec.get("strategy")
    if strategy not in _allocators:
        raise AllocatorNotFoundError(
            f"No allocator registered for strategy {strategy!r}. "
            f"Available: {list(_allocators.keys())}"
        )
    return _allocators[strategy](spec)


def registered_selectors():
    return dict(_selectors)


def registered_allocators():
    return dict(_allocators)