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Jackson 2.x module for handling versioning of models.
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/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Jon Peterson
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.github.jonpeterson.jackson.module.versioning;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.introspect.BeanPropertyDefinition;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.databind.ser.ResolvableSerializer;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

public class VersionedModelSerializer extends StdSerializer implements ResolvableSerializer {
    private final StdSerializer delegate;
    private final JsonVersionedModel jsonVersionedModel;
    private final VersionedModelConverter converter;
    private final BeanPropertyDefinition serializeToVersionProperty;

    public VersionedModelSerializer(StdSerializer delegate, JsonVersionedModel jsonVersionedModel, BeanPropertyDefinition serializeToVersionProperty) {
        super(delegate.handledType());

        this.delegate = delegate;
        this.jsonVersionedModel = jsonVersionedModel;
        this.serializeToVersionProperty = serializeToVersionProperty;

        Class converterClass = jsonVersionedModel.toPastConverterClass();
        if(converterClass != VersionedModelConverter.class)
            try {
                this.converter = converterClass.newInstance();
            } catch(Exception e) {
                throw new RuntimeException("unable to create instance of converter '" + converterClass.getName() + "'", e);
            }
        else
            converter = null;
    }

    @Override
    public void resolve(SerializerProvider provider) throws JsonMappingException {
        if(delegate instanceof ResolvableSerializer)
            ((ResolvableSerializer)delegate).resolve(provider);
    }

    @Override
    public void serialize(T value, JsonGenerator generator, SerializerProvider provider) throws IOException {
        doSerialize(value, generator, provider, null);
    }

    @Override
    public void serializeWithType(T value, JsonGenerator generator, SerializerProvider provider, TypeSerializer typeSerializer) throws IOException {
        doSerialize(value, generator, provider, typeSerializer);
    }

    private void doSerialize(T value, JsonGenerator generator, SerializerProvider provider, TypeSerializer typeSerializer) throws IOException {
        // serialize the value into a byte array buffer then parse it back out into a JsonNode tree
        // TODO: find a better way to convert the value into a tree
        JsonFactory factory = generator.getCodec().getFactory();
        ByteArrayOutputStream buffer = new ByteArrayOutputStream(4096);
        JsonGenerator bufferGenerator = factory.createGenerator(buffer);
        try {
            if(typeSerializer != null)
                delegate.serializeWithType(value, bufferGenerator, provider, typeSerializer);
            else
                delegate.serialize(value, bufferGenerator, provider);
        } finally {
            bufferGenerator.close();
        }

        ObjectNode modelData = factory.createParser(buffer.toByteArray()).readValueAsTree();

        // set target version to @SerializeToVersion's value, @JsonVersionModel's defaultSerializeToVersion, or
        //   @JsonVersionModel's currentVersion in that order
        String targetVersion = null;
        if(serializeToVersionProperty != null) {
            targetVersion = (String)serializeToVersionProperty.getAccessor().getValue(value);
            modelData.remove(serializeToVersionProperty.getName());
        }
        if(targetVersion == null)
            targetVersion = jsonVersionedModel.defaultSerializeToVersion();
        if(targetVersion.isEmpty())
            targetVersion = jsonVersionedModel.currentVersion();

        // convert model data if there is a converter and targetVersion is different than the currentVersion or if
        //   alwaysConvert is true
        if(converter != null && (jsonVersionedModel.alwaysConvert() || !targetVersion.equals(jsonVersionedModel.currentVersion())))
            modelData = converter.convert(modelData, jsonVersionedModel.currentVersion(), targetVersion, JsonNodeFactory.instance);

        // add target version to model data if it wasn't the version to suppress
        if(!targetVersion.equals(jsonVersionedModel.versionToSuppressPropertySerialization()))
            modelData.put(jsonVersionedModel.propertyName(), targetVersion);

        // write node
        generator.writeTree(modelData);
    }
}