from Crypto.Cipher import Blowfish


def encode_dataset_user( trans, dataset, user ):
    # encode dataset id as usual
    # encode user id using the dataset create time as the key
    dataset_hash = trans.security.encode_id( dataset.id )
    if user is None:
        user_hash = 'None'
    else:
        user_hash = str( user.id )
        # Pad to a multiple of 8 with leading "!"
        user_hash = ( "!" * ( 8 - len( user_hash ) % 8 ) ) + user_hash
        cipher = Blowfish.new( str( dataset.create_time ) )
        user_hash = cipher.encrypt( user_hash ).encode( 'hex' )
    return dataset_hash, user_hash


def decode_dataset_user( trans, dataset_hash, user_hash ):
    # decode dataset id as usual
    # decode user id using the dataset create time as the key
    dataset_id = trans.security.decode_id( dataset_hash )
    dataset = trans.sa_session.query( trans.app.model.HistoryDatasetAssociation ).get( dataset_id )
    assert dataset, "Bad Dataset id provided to decode_dataset_user"
    if user_hash in [ None, 'None' ]:
        user = None
    else:
        cipher = Blowfish.new( str( dataset.create_time ) )
        user_id = cipher.decrypt( user_hash.decode( 'hex' ) ).lstrip( "!" )
        user = trans.sa_session.query( trans.app.model.User ).get( int( user_id ) )
        assert user, "A Bad user id was passed to decode_dataset_user"
    return dataset, user