# Credits to
# https://tenthousandmeters.com/blog/python-behind-the-scenes-11-how-the-python-import-system-works/
# for the very good explanation of how Python’s import statement works.

import sys, os
from importlib.abc import MetaPathFinder
from importlib.machinery import SourceFileLoader, ModuleSpec, PathFinder

class GuixPythonFinder (MetaPathFinder):
    def find_spec (self, fullname, path, target=None):
        # Short-circuit for non-top-level imports, which already have a path.
        if path:
            return None

        attrname = '__guix_pythonpath__'
        searchPath = None
        # Search for our caller.
        frame = sys._getframe ()
        while frame:
            # If he has a search path, use it. This is mainly for executable
            # scripts with `__name__ == '__main__'`.
            searchPath = frame.f_globals.get (attrname, None)
            if not searchPath:
                # Otherwise check the top-level package for search paths
                # declared in __init__.py
                package = frame.f_globals.get ('__package__')
                if package:
                    module = sys.modules.get (package)
                    if module:
                        searchPath = getattr (module, attrname, None)
            if searchPath is not None:
                break
            frame = frame.f_back

        # If we have a caller…
        if searchPath is not None:
            return PathFinder.find_spec (fullname, searchPath, target=target)
        else:
            # Otherwise we’re not responsible for this module.
            return None

sys.meta_path.insert (0, GuixPythonFinder ())