#!/usr/bin/env python
#
# Copyright 2014 Tuenti Technologies S.L.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

import sys
import logging

logger = logging.getLogger(__name__)


def get_class_from_name(clazz_name):
    """
    Returns a valid class, if it exists, from a module name + class name.

    @param module: str with the name of the module
    @return: a valid class.
    """
    logger.debug("Loading class: %s" % clazz_name)
    module_name, clazz_name = clazz_name.rsplit('.', 1)
    module = import_module(module_name)
    return module.__getattribute__(clazz_name)


"""Backport of importlib.import_module from 3.x."""
# While not critical (and in no way guaranteed!), it would be nice to keep this
# code compatible with Python 2.3.


def _resolve_name(name, package, level):
    """Return the absolute name of the module to be imported."""
    if not hasattr(package, 'rindex'):
        raise ValueError("'package' not set to a string")
    dot = len(package)
    for x in xrange(level, 1, -1):
        try:
            dot = package.rindex('.', 0, dot)
        except ValueError:
            raise ValueError("attempted relative import beyond top-level "
                             "package")
    return "%s.%s" % (package[:dot], name)


def import_module(name, package=None):
    """Import a module.

    The 'package' argument is required when performing a relative import. It
    specifies the package to use as the anchor point from which to resolve the
    relative import to an absolute import.

    """
    if name.startswith('.'):
        if not package:
            raise TypeError("relative imports require the 'package' argument")
        level = 0
        for character in name:
            if character != '.':
                break
            level += 1
        name = _resolve_name(name[level:], package, level)
    __import__(name)
    return sys.modules[name]
