"""Utility code for constructing importers, etc."""

from ._bootstrap import MAGIC_NUMBER
from ._bootstrap import cache_from_source
from ._bootstrap import decode_source
from ._bootstrap import module_to_load
from ._bootstrap import set_loader
from ._bootstrap import set_package
from ._bootstrap import source_from_cache
from ._bootstrap import _resolve_name

import functools
import warnings


def resolve_name(name, package):
    """Resolve a relative module name to an absolute one."""
    if not name.startswith('.'):
        return name
    elif not package:
        raise ValueError('{!r} is not a relative name '
                         '(no leading dot)'.format(name))
    level = 0
    for character in name:
        if character != '.':
            break
        level += 1
    return _resolve_name(name[level:], package, level)


def module_for_loader(fxn):
    """Decorator to handle selecting the proper module for loaders.

    The decorated function is passed the module to use instead of the module
    name. The module passed in to the function is either from sys.modules if
    it already exists or is a new module. If the module is new, then __name__
    is set the first argument to the method, __loader__ is set to self, and
    __package__ is set accordingly (if self.is_package() is defined) will be set
    before it is passed to the decorated function (if self.is_package() does
    not work for the module it will be set post-load).

    If an exception is raised and the decorator created the module it is
    subsequently removed from sys.modules.

    The decorator assumes that the decorated function takes the module name as
    the second argument.

    """
    warnings.warn('To make it easier for subclasses, please use '
                  'importlib.util.module_to_load() and '
                  'importlib.abc.Loader.init_module_attrs()',
                  PendingDeprecationWarning, stacklevel=2)
    @functools.wraps(fxn)
    def module_for_loader_wrapper(self, fullname, *args, **kwargs):
        with module_to_load(fullname) as module:
            module.__loader__ = self
            try:
                is_package = self.is_package(fullname)
            except (ImportError, AttributeError):
                pass
            else:
                if is_package:
                    module.__package__ = fullname
                else:
                    module.__package__ = fullname.rpartition('.')[0]
            # If __package__ was not set above, __import__() will do it later.
            return fxn(self, module, *args, **kwargs)

    return module_for_loader_wrapper
