cycles_fixup.py

"""Sole purpose of this thing - fix circular imports.
Consider, for example, message:

`slonogram.schemas.message.Message` depends on `slonogram.schemas.chat.Chat`
`Chat` also depends on `Message`, so that we got logically unsolvable circular imports problem.

This is the solution to it.
"""
from typing import Any, Iterable
from importlib import import_module

class _ImportTarget:
    __slots__ = ('module', )

    def __init__(self, module: str) -> None:
        self.module = module
    
    def import_name(self, name: str) -> Any:
        return getattr(import_module(self.module), name)


class LazilyImported:
    keys: list[str]
    data: dict[str, _ImportTarget | Any]

    __slots__ = ('keys', 'data')

    def __init__(self, items: Iterable[str]) -> None:
        keys: list[str] = []
        data: dict[str, _ImportTarget | Any] = {}

        for item in items:
            object_dot = item.rfind('.')
            if object_dot == -1:
                raise ValueError(f'Module name {item!r} does not contain any dot: import target not known')
            module = item[:object_dot]
            name = item[object_dot+1:]

            data[name] = _ImportTarget(module)
            keys.append(name)

        self.data = data
        self.keys = keys

    def __getattr__(self, name: str) -> Any:
        value = self.data[name]
        if type(value) is _ImportTarget:
            imported = value.import_name(name)
            self.data[name] = imported
            return imported
        return value

    def __dir__(self) -> list[str]:
        return self.keys


__all__ = ["LazilyImported"]