def tcl_delta_filename(curef, fvver, tvver, filename, original=True):
    """
    Generate compatible filenames for deltas, if needed.

    :param curef: PRD of the phone variant to check.
    :type curef: str

    :param fvver: Initial software version.
    :type fvver: str

    :param tvver: Target software version.
    :type tvver: str

    :param filename: File name from download URL, passed through if not changing filename.
    :type filename: str

    :param original: If we'll download the file with its original filename. Default is True.
    :type original: bool
    """
    if not original:
        prdver = curef.split("-")[1]
        filename = "JSU_PRD-{0}-{1}to{2}.zip".format(prdver, fvver, tvver)
    return filename