/*******************************************************************************
 * Copyright (c) 2015-2019 Skymind, Inc.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Apache License, Version 2.0 which is available at
 * https://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 * SPDX-License-Identifier: Apache-2.0
 ******************************************************************************/

package org.nd4j.linalg.api.ops.impl.transforms.custom;

import lombok.NoArgsConstructor;
import org.nd4j.autodiff.samediff.SDVariable;
import org.nd4j.autodiff.samediff.SameDiff;
import org.nd4j.base.Preconditions;
import org.nd4j.linalg.api.buffer.DataType;
import org.nd4j.linalg.api.ops.DynamicCustomOp;

import java.util.Arrays;
import java.util.List;


/**
 * (optionally scaled) dot product attention Backprop
 *
 * See also "Attention is all you need" (https://arxiv.org/abs/1706.03762, p. 4, eq. 1)
 *
 * @author Paul Dubs
 */
@NoArgsConstructor
public class DotProductAttentionBp extends DynamicCustomOp {

    private boolean scaled;

    public DotProductAttentionBp(SameDiff sameDiff, SDVariable queries, SDVariable keys, SDVariable values, SDVariable eps, SDVariable mask, boolean scaled) {
        super(null, sameDiff, mask == null ? new SDVariable[] {queries, keys, values, eps} : new SDVariable[] {queries, keys, values, eps, mask}, false);
        this.scaled = scaled;
        addIArgument(scaled ? 1 : 0);
    }

    @Override
    public String opName() {
        return "dot_product_attention_bp";
    }

    @Override
    public List<SDVariable> doDiff(List<SDVariable> grad){
        throw new UnsupportedOperationException("Differentiation of " + getClass().getName() + " not supported");
    }

    @Override
    public List<DataType> calculateOutputDataTypes(List<DataType> dataTypes){
        Preconditions.checkState(dataTypes != null && (dataTypes.size() == 4 || dataTypes.size() == 5), "Expected 4 or 5 input datatypes, got %s", dataTypes);
        DataType first = dataTypes.get(0);
        for( int i=0; i<dataTypes.size(); i++ ) {
            Preconditions.checkState(dataTypes.get(i).isFPType(), "Input %s datatype must be a floating point type, got datypes %s", dataTypes);
            if(i > 0){
                Preconditions.checkState(first == dataTypes.get(i), "All datatypes must be same type, got input datatypes %s", dataTypes);
            }
        }

        return Arrays.asList(first, first, first);
    }
}
