def base_url_for(path, revision):
    """Create a base URL for path and requested revision.

    Keyword arguments:
        path (string): A path from Ember application is served.
        revision (string): A requested revision.

    Returns:
        A base URL.

    """
    if revision == 'current':
        return path
    return '{0}r/{1}/'.format(path, revision)
