import os

from os.path import join, normcase, normpath, abspath, isabs, sep

from django.utils.encoding import force_unicode

# Define our own abspath function that can handle joining 

# unicode paths to a current working directory that has non-ASCII

# characters in it.  This isn't necessary on Windows since the 

# Windows version of abspath handles this correctly.  The Windows

# abspath also handles drive letters differently than the pure 

# Python implementation, so it's best not to replace it.

if os.name == 'nt':

    abspathu = abspath

else:

    def abspathu(path):

        """

        Version of os.path.abspath that uses the unicode representation

        of the current working directory, thus avoiding a UnicodeDecodeError

        in join when the cwd has non-ASCII characters.

        """

        if not isabs(path):

            path = join(os.getcwdu(), path)

        return normpath(path)

def safe_join(base, *paths):

    """

    Joins one or more path components to the base path component intelligently.

    Returns a normalized, absolute version of the final path.

    The final path must be located inside of the base path component (otherwise

    a ValueError is raised).

    """

    # We need to use normcase to ensure we don't false-negative on case

    # insensitive operating systems (like Windows).

    base = force_unicode(base)

    paths = [force_unicode(p) for p in paths]

    final_path = normcase(abspathu(join(base, *paths)))

    base_path = normcase(abspathu(base))

    base_path_len = len(base_path)

    # Ensure final_path starts with base_path and that the next character after

    # the final path is os.sep (or nothing, in which case final_path must be

    # equal to base_path).

    if not final_path.startswith(base_path) \

       or final_path[base_path_len:base_path_len+1] not in ('', sep):

        raise ValueError('the joined path is located outside of the base path'

                         ' component')

    return final_path