/*
 * ============LICENSE_START=======================================================
 * ONAP
 * ================================================================================
 * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://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.
 * ============LICENSE_END=========================================================
 */

package org.onap.policy.common.gson;

import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import org.onap.policy.common.gson.internal.ClassWalker;
import org.onap.policy.common.gson.internal.Deserializer;
import org.onap.policy.common.gson.internal.FieldDeserializer;
import org.onap.policy.common.gson.internal.FieldSerializer;
import org.onap.policy.common.gson.internal.Serializer;

/**
 * Factory that serializes/deserializes class fields following the normal behavior of
 * jackson. Supports the following annotations:
 * <ul>
 * <li>GsonJsonIgnore</li>
 * <li>GsonJsonProperty</li>
 * </ul>
 *
 * <p>Note: {@link JacksonExclusionStrategy} must also be registered with the gson object.
 */
public class JacksonFieldAdapterFactory implements TypeAdapterFactory {

    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        Class<? super T> clazz = type.getRawType();

        if (!JacksonExclusionStrategy.isManaged(clazz)) {
            return null;
        }

        ClassWalker data = new ClassWalker();
        data.walkClassHierarchy(clazz);

        if (data.getInProps(Field.class).isEmpty() && data.getOutProps(Field.class).isEmpty()) {
            // no fields to serialize
            return null;
        }

        return new JacksonFieldAdapter<>(gson, data, gson.getDelegateAdapter(this, type));
    }

    /**
     * Adapter for a single class.
     *
     * @param <T> type of class on which the adapter works
     */
    private static class JacksonFieldAdapter<T> extends TypeAdapter<T> {

        /**
         * Used to create an object of the given class.
         */
        private final TypeAdapter<T> delegate;

        /**
         * Used to serialize/deserialize a JsonElement.
         */
        private final TypeAdapter<JsonElement> elementAdapter;

        /**
         * Serializers for each item within the object.
         */
        private final Serializer[] serializers;

        /**
         * Deserializers for each item within the object.
         */
        private final Deserializer[] deserializers;

        /**
         * Constructs the object.
         *
         * @param gson the associated gson object
         * @param data data used to configure the adapter
         * @param delegate default constructor for the type
         */
        public JacksonFieldAdapter(Gson gson, ClassWalker data, TypeAdapter<T> delegate) {
            this.delegate = delegate;

            this.elementAdapter = gson.getAdapter(JsonElement.class);

            // create serializers
            this.serializers = makeSerializers(gson, data).toArray(new Serializer[0]);

            // create deserializers
            this.deserializers = makeDeserializers(gson, data).toArray(new Deserializer[0]);
        }

        /**
         * Creates a complete list of serializers.
         *
         * @param gson the associated gson object
         * @param data data used to configure the serializers
         * @return a list of all serializers
         */
        private List<Serializer> makeSerializers(Gson gson, ClassWalker data) {
            List<Serializer> ser = new ArrayList<Serializer>();

            data.getOutProps(Field.class).forEach(field -> ser.add(new FieldSerializer(gson, field)));

            return ser;
        }

        /**
         * Creates a complete list of deserializers.
         *
         * @param gson the associated gson object
         * @param data data used to configure the deserializers
         * @return a list of all deserializers
         */
        private List<Deserializer> makeDeserializers(Gson gson, ClassWalker data) {
            List<Deserializer> deser = new ArrayList<Deserializer>();

            data.getInProps(Field.class).forEach(field -> deser.add(new FieldDeserializer(gson, field)));

            return deser;
        }

        @Override
        public void write(JsonWriter out, T value) throws IOException {
            JsonElement tree = delegate.toJsonTree(value);

            if (tree.isJsonObject()) {
                JsonObject jsonObj = tree.getAsJsonObject();

                // serialize each item from the value into the target tree
                for (Serializer serializer : serializers) {
                    serializer.addToTree(value, jsonObj);
                }
            }

            elementAdapter.write(out, tree);
        }

        @Override
        public T read(JsonReader in) throws IOException {
            JsonElement tree = elementAdapter.read(in);
            T object = delegate.fromJsonTree(tree);

            if (tree.isJsonObject()) {
                JsonObject jsonObj = tree.getAsJsonObject();

                // deserialize each item from the tree into the target object
                for (Deserializer dser : deserializers) {
                    dser.getFromTree(jsonObj, object);
                }
            }

            return object;
        }
    }
}