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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2013-2016 Amazon.com, Inc. or its affiliates. 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://aws.amazon.com/apache2.0
 *
 * This file 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.
 */
package com.amazonaws.services.dynamodbv2.datamodeling;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import com.amazonaws.services.dynamodbv2.model.AttributeValue;

/**
 * A virtual {@code AttributeTransformer} that transforms and untransforms
 * attributes by running them through a cascading series of child
 * {@code AttributeTransformer} instances.
 */
public class AttributeTransformerChain implements AttributeTransformer {

    private final List transformers;

    /**
     * Creates a new transformer chain from the given array of transformers.
     * When transforming attributes, these transformers are invoked from first
     * to last; when untransforming they are invoked in the opposite order.
     *
     * @param transformers the chain of transformers.
     */
    public AttributeTransformerChain(
            final AttributeTransformer... transformers) {

        this(Arrays.asList(transformers));
    }

    /**
     * Creates a new transformer chain from the given list of transformers.
     * When transforming attributes, these transformers are invoked from first
     * to last; when untransforming they are invoked in the opposite order.
     *
     * @param transformers the chain of transformers.
     */
    public AttributeTransformerChain(
            final List transformers) {

        this.transformers = Collections.unmodifiableList(
            new ArrayList(transformers));
    }

    /**
     * @return the transformers in this chain
     */
    public List getTransformers() {
        return transformers;
    }

    @Override
    public Map transform(
            final Parameters parameters) {

        ProxyParameters proxy = new ProxyParameters(parameters);

        for (int i = 0; i < transformers.size(); ++i) {
            proxy.setAttributeValues(transformers.get(i).transform(proxy));
        }

        return proxy.getAttributeValues();
    }

    @Override
    public Map untransform(
            final Parameters parameters) {

        ProxyParameters proxy = new ProxyParameters(parameters);

        for (int i = transformers.size() - 1; i >= 0; --i) {
            proxy.setAttributeValues(transformers.get(i).untransform(proxy));
        }

        return proxy.getAttributeValues();
    }

    @Override
    public String toString() {
        return transformers.toString();
    }

    /**
     * A {@code Parameters} proxy that intercepts calls to
     * {@code getAttributeValues} and overrides the return value.
     */
    private static class ProxyParameters implements Parameters {

        private final Parameters delegate;
        private Map values;

        /**
         * Create a new proxy wrapping the given {@code Parameters} object.
         *
         * @param delegate the parameters object to wrap
         */
        public ProxyParameters(final Parameters delegate) {
            this.delegate = delegate;
            this.values = delegate.getAttributeValues();
        }

        @Override
        public Map getAttributeValues() {
            return values;
        }

        /**
         * Changes the attribute values for this instance.
         *
         * @param values the new values
         */
        public void setAttributeValues(
                final Map values) {
            this.values = Collections.unmodifiableMap(values);
        }

        @Override
        public boolean isPartialUpdate() {
            return delegate.isPartialUpdate();
        }

        @Override
        public Class getModelClass() {
            return delegate.getModelClass();
        }

        @Override
        public DynamoDBMapperConfig getMapperConfig() {
            return delegate.getMapperConfig();
        }

        @Override
        public String getTableName() {
            return delegate.getTableName();
        }

        @Override
        public String getHashKeyName() {
            return delegate.getHashKeyName();
        }

        @Override
        public String getRangeKeyName() {
            return delegate.getRangeKeyName();
        }
    }
}