from abc import ABC, abstractmethod


class ScreenshotBackend(ABC):
    @abstractmethod
    def supports(self) -> bool:
        pass

    @abstractmethod
    def active_window(self) -> str:
        pass


_backends = []


def register_backend(cls):
    _backends.append(cls())
    return cls


def get_backend() -> ScreenshotBackend:
    for backend in _backends:
        if backend.supports():
            return backend
    raise RuntimeError("No screenshot backend available")