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

from django.utils.encoding import force_unicode

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(abspath(join(base, *paths)))

    base_path = normcase(abspath(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