':param category: audio|image|office|text|video
:param extension: file extension
:param depth: depth of the file (depth >= 0)'

@classmethod
def file_path(cls, depth=1, category=None, extension=None):

    file = Provider.file_name(category, extension)
    path = u'/{0}'.format(file)
    for d in range(0, depth):
        path = u'/{0}{1}'.format(WordProvider.word(), path)
    return path
