def sentinel2_toa_cloud_mask(input_img):
    """Extract cloud mask from the Sentinel 2 TOA QA60 band

    Parameters
    ----------
    input_img : ee.Image
        Image from the COPERNICUS/S2 collection with a QA60 band.

    Returns
    -------
    ee.Image

    Notes
    -----
    Output image is structured to be applied directly with updateMask()
        i.e. 0 is cloud, 1 is cloud free

    Bits
        10: Opaque clouds present
        11: Cirrus clouds present

    The Sentinel 2 TOA and SR cloud masks functions are currently identical

    References
    ----------
    https://sentinel.esa.int/documents/247904/685211/Sentinel-2_User_Handbook
    https://sentinel.esa.int/web/sentinel/technical-guides/sentinel-2-msi/level-1c/cloud-masks

    """
    qa_img = input_img.select(['QA60'])
    cloud_mask = qa_img.rightShift(10).bitwiseAnd(1).neq(0)\
        .Or(qa_img.rightShift(11).bitwiseAnd(1).neq(0))

    # Set cloudy pixels to 0 and clear to 1
    return cloud_mask.Not()