/*******************************************************************************
 * Copyright (c) 2015-2018 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.deeplearning4j.nn.gradient;

import lombok.Setter;
import org.nd4j.linalg.api.ndarray.INDArray;
import org.nd4j.linalg.factory.Nd4j;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

/**
 * Default gradient implementation. Basically lookup table
 * for ndarrays
 *
 * @author Adam Gibson
 */

public class DefaultGradient implements Gradient {
    public static final char DEFAULT_FLATTENING_ORDER = 'f';
    private Map<String, INDArray> gradients = new LinkedHashMap<>();
    private Map<String, Character> flatteningOrders;
    @Setter
    private INDArray flattenedGradient;

    public DefaultGradient() {}

    public DefaultGradient(INDArray flattenedGradient) {
        this.flattenedGradient = flattenedGradient;
    }

    @Override
    public Map<String, INDArray> gradientForVariable() {
        return gradients;
    }

    @Override
    public INDArray gradient(List<String> order) {
        List<INDArray> toFlatten = new ArrayList<>();
        if (flatteningOrders == null) {
            for (String s : order) {
                if (!gradients.containsKey(s))
                    continue;
                toFlatten.add(gradients.get(s));
            }
        } else {
            for (String s : order) {
                if (!gradients.containsKey(s))
                    continue;
                if (flatteningOrders.containsKey(s) && flatteningOrders.get(s) != DEFAULT_FLATTENING_ORDER) {
                    //Arrays with non-default order get flattened to row vector first, then everything is flattened to f order
                    //TODO revisit this, and make more efficient
                    toFlatten.add(Nd4j.toFlattened(flatteningOrders.get(s), gradients.get(s)));
                } else {
                    toFlatten.add(gradients.get(s));
                }
            }
        }
        INDArray ret = Nd4j.toFlattened(DEFAULT_FLATTENING_ORDER, toFlatten);
        return ret.reshape('c', 1, ret.length());
    }

    private void flattenGradient() {
        if (flatteningOrders != null) {
            //Arrays with non-default order get flattened to row vector first, then everything is flattened to f order
            //TODO revisit this, and make more efficient
            List<INDArray> toFlatten = new ArrayList<>();
            for (Map.Entry<String, INDArray> entry : gradients.entrySet()) {
                if (flatteningOrders.containsKey(entry.getKey())
                                && flatteningOrders.get(entry.getKey()) != DEFAULT_FLATTENING_ORDER) {
                    //Specific flattening order for this array, that isn't the default
                    toFlatten.add(Nd4j.toFlattened(flatteningOrders.get(entry.getKey()), entry.getValue()));
                } else {
                    //default flattening order for this array
                    toFlatten.add(entry.getValue());
                }
            }
            flattenedGradient = Nd4j.toFlattened(DEFAULT_FLATTENING_ORDER, toFlatten);
        } else if( !gradients.values().isEmpty() ){ //Edge case: can be empty for nets with 0 params
            //Standard case: flatten all to f order
            flattenedGradient = Nd4j.toFlattened(DEFAULT_FLATTENING_ORDER, gradients.values());

        }
        if(flattenedGradient.rank() == 1){
            flattenedGradient = flattenedGradient.reshape('c', 1, flattenedGradient.length());
        }
    }

    @Override
    public INDArray gradient() {
        if (flattenedGradient != null)
            return flattenedGradient;
        flattenGradient();
        return flattenedGradient;
    }

    @Override
    public void clear() {
        gradients.clear();
    }

    @Override
    public INDArray getGradientFor(String variable) {
        return gradients.get(variable);
    }

    @Override
    public INDArray setGradientFor(String variable, INDArray newGradient) {
        INDArray last = gradients.put(variable, newGradient);
        // TODO revisit whether setGradientFor should update the gradient that can be pulled from this object in any form - currently does not update flattened
        // use of unitialized var for flattengradient in backprop is generating an error in gradient calc if bellow is used
        //        flattenGradient();
        return last;
    }

    @Override
    public INDArray setGradientFor(String variable, INDArray gradient, Character flatteningOrder) {
        INDArray last = setGradientFor(variable, gradient);

        if (flatteningOrder != null) {
            if (flatteningOrders == null)
                flatteningOrders = new LinkedHashMap<>();
            flatteningOrders.put(variable, flatteningOrder);
        }
        return last;
    }

    @Override
    public Character flatteningOrderForVariable(String variable) {
        if (flatteningOrders == null)
            return null;
        return flatteningOrders.get(variable);
    }


    @Override
    public String toString() {
        return "DefaultGradient{" + "gradients=" + gradients + (flatteningOrders != null ? flatteningOrders : "") + '}';
    }
}
