import sys, imp, os

from importlib._bootstrap import set_package, set_loader, FileFinder
from importlib._bootstrap import ExtensionFileLoader, SourceFileLoader
from importlib._bootstrap import SourcelessFileLoader
from importlib._bootstrap import SOURCE_SUFFIXES, BYTECODE_SUFFIXES

class WindowsRegistryImporter:

    """Meta path import for modules declared in the Windows registry.
    """

    REGISTRY_KEY = ("Software\\Python\\PythonCore\\{sys_version}"
                    "\\Modules\\{fullname}")
    if '_d.pyd' in imp.extension_suffixes():
        REGISTRY_KEY += "\\Debug"

    @classmethod
    def _open_registry(cls, key):
        try:
            return winreg.OpenKey(winreg.HKEY_CURRENT_USER, key)
        except WindowsError:
            return winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, key)

    @classmethod
    def _search_registry(cls, fullname):
        key = cls.REGISTRY_KEY.format(fullname=fullname,
                                      sys_version=sys.version[:3])
        try:
            with cls._open_registry(key) as hkey:
                fullname = winreg.QueryValue(hkey, "")
        except WindowsError:
            return None
        return fullname

    # XXX reuse code from _bootstrap._install()
    LOADERS = [
        (ExtensionFileLoader, imp.extension_suffixes()),
        (SourceFileLoader, SOURCE_SUFFIXES),
        (SourcelessFileLoader, BYTECODE_SUFFIXES)]

    @classmethod
    def find_module(cls, fullname, path=None):
        """Find module named in the registry."""
        full_path = cls._search_registry(fullname)
        if full_path is None:
            return None
        try:
            os.stat(full_path)
        except OSError:
            return None
        for loader, suffixes in cls.LOADERS:
            if full_path.endswith(tuple(suffixes)):
                return loader(fullname, full_path)
        
sys.meta_path.append(WindowsRegistryImporter)


# A small fake winreg implementation for non-windows platforms...
try:
    WindowsError
    import winreg
except (ImportError, NameError):
    WindowsError = ValueError
    class winreg:
        FAKE_REGISTRY = {
            r"Software\Python\PythonCore\3.3\Modules\from_registry":
                "/home/amauryfa/python/cpython3.x/setup.py",
            }

        HKEY_CURRENT_USER = "HKCU"
        HKEY_LOCAL_MACHINE = "HKLM"

        @staticmethod
        def OpenKey(root, key):
            if key in winreg.FAKE_REGISTRY:
                return winreg(key)
            else:
                raise WindowsError

        def QueryValue(self, subkey):
            assert not subkey
            return winreg.FAKE_REGISTRY[self.key]

        def __init__(self, key):
            self.key = key

        def __enter__(self):
            return self
        def __exit__(self, *args):
            pass

# Test it!
import from_registry
print(from_registry)