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/*******************************************************************************
 * 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.nd4j.serde.json;

import lombok.extern.slf4j.Slf4j;
import org.nd4j.shade.jackson.core.JsonParser;
import org.nd4j.shade.jackson.databind.DeserializationContext;
import org.nd4j.shade.jackson.databind.JsonDeserializer;
import org.nd4j.shade.jackson.databind.JsonNode;
import org.nd4j.shade.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

/**
 * A base deserialization class used to handle deserializing of a specific class given changes from subtype wrapper
 * format to class field format.

 * That is: from...

 * {@literal {@code @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.WRAPPER_OBJECT)}}

 * {@literal {@code @JsonSubTypes(value = {@JsonSubTypes.Type(value = LossBinaryXENT.class, name = "BinaryXENT"),}...}}

 * 

 * to

 * 

 * {@literal {@code @JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")}}
 *
 * @param   Type to deserialize
 * @author Alex Black
 */
@Slf4j
public abstract class BaseLegacyDeserializer extends JsonDeserializer {

    public abstract Map getLegacyNamesMap();

    public abstract ObjectMapper getLegacyJsonMapper();

    public abstract Class getDeserializedType();

    @Override
    public T deserialize(JsonParser jp, DeserializationContext deserializationContext) throws IOException {
        //Manually parse old format
        JsonNode node = jp.getCodec().readTree(jp);

        Iterator> nodes = node.fields();

        List> list = new ArrayList<>();
        while(nodes.hasNext()){
            list.add(nodes.next());
        }

        if(list.size() != 1){
            //Should only occur if field is null?
            return null;
        }

        String name = list.get(0).getKey();
        JsonNode value = list.get(0).getValue();

        Map legacyNamesMap = getLegacyNamesMap();
        String layerClass = legacyNamesMap.get(name);
        if(layerClass == null){
            throw new IllegalStateException("Cannot deserialize " + getDeserializedType() + " with name \"" + name
                    + "\": legacy class mapping with this name is unknown");
        }

        Class lClass;
        try {
            lClass = (Class) Class.forName(layerClass);
        } catch (Exception e){
            throw new RuntimeException("Could not find class for deserialization of \"" + name + "\" of type " +
                    getDeserializedType() + ": class " + layerClass + " is not on the classpath?", e);
        }

        ObjectMapper m = getLegacyJsonMapper();

        if(m == null){
            //Should never happen, unless the user is doing something unusual
            throw new IllegalStateException("Cannot deserialize unknown subclass of type " +
                    getDeserializedType() + ": no legacy JSON mapper has been set");
        }

        String nodeAsString = value.toString();
        try {
            T t = m.readValue(nodeAsString, lClass);
            return t;
        } catch (Throwable e){
            throw new IllegalStateException("Cannot deserialize legacy JSON format of object with name \"" + name
                    + "\" of type " + getDeserializedType().getName(), e);
        }
    }



}