import collections.abc
import pathlib

__all__ = ('root',)


class AttrsView(collections.abc.KeysView):
    def __init__(self, root):
        self._root = pathlib.Path(root)

    def __repr__(self):
        return f"{type(self).__name__}({str(self._root)!r})"

    def __len__(self):
        return sum(1 for _ in self)

    def __contains__(self, key):
        return (self._root / key).is_file()

    def __iter__(self):
        for subitem in self._root.iterdir():
            if subitem.is_file():
                yield subitem.name


class SysFsNode(collections.abc.Mapping):
    def __init__(self, path):
        self._root = pathlib.Path(path)

    def __repr__(self):
        return f"{type(self).__name__}({str(self._root)!r})"

    def __getitem__(self, key):
        subitem = self._root / key
        if subitem.is_dir():
            return type(self)(subitem)
        else:
            raise KeyError(f"Key {key} does not exist")

    def __iter__(self):
        for subitem in self._root.iterdir():
            if subitem.is_dir():
                yield subitem.name

    def __len__(self):
        return sum(1 for _ in self)

    def __contains__(self, key):
        return (self._root / key).is_dir()

    def __getattr__(self, name):
        try:
            return (self._root / name).read_text().strip()
        except FileNotFoundError:
            raise AttributeError(f"Attribute {name} does not exist")

    def attrs(self):
        return AttrsView(self._root)

    def __dir__(self):
        yield from super().__dir__()
        yield from self.attrs()


root = SysFsNode('/sys')