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The Amazon DynamoDB Storage Backend for JanusGraph: This is an updated version that works with a later version of JanusGraph Distributed Graph Database allows JanusGraph graphs to use DynamoDB as a storage backend.

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/*
 * Copyright 2014-2018 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.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. 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.amazon.janusgraph.diskstorage.dynamodb.builder;

import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import org.janusgraph.diskstorage.Entry;
import org.janusgraph.diskstorage.StaticBuffer;
import org.janusgraph.diskstorage.util.BufferUtil;
import org.janusgraph.diskstorage.util.StaticArrayEntry;

import com.amazon.janusgraph.diskstorage.dynamodb.Constants;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;

import lombok.Setter;
import lombok.experimental.Accessors;

/**
 * EntryBuilder is responsible for translating from DynamoDB item maps to Entry
 * objects.
 *
 * @author Matthew Sowders
 * @author Alexander Patrikalakis
 *
 */
public class EntryBuilder extends AbstractBuilder {
    private final Map item;
    private StaticBuffer start;
    private StaticBuffer end;
    private boolean slice;
    @Setter
    @Accessors(fluent = true)
    private int limit = Integer.MAX_VALUE;

    public EntryBuilder(final Map item) {
        this.item = item;
        item.remove(Constants.JANUSGRAPH_HASH_KEY);
    }

    public List buildAll() {
        if (null == item) {
            return Collections.emptyList();
        }
        final Entry sliceStartEntry;
        final Entry sliceEndEntry;
        if (slice) {
            sliceStartEntry = StaticArrayEntry.of(start, BufferUtil.emptyBuffer());
            sliceEndEntry = StaticArrayEntry.of(end, BufferUtil.emptyBuffer());
        } else {
            sliceStartEntry = null;
            sliceEndEntry = null;
        }
        //TODO(amcp) Arrays.parallelSort(filteredEntries)?
        //https://github.com/awslabs/dynamodb-titan-storage-backend/issues/159
        return item.entrySet().stream()
            .map(entry -> {
                final StaticBuffer columnKey = decodeKey(entry.getKey());
                final AttributeValue valueValue = entry.getValue();
                final StaticBuffer value = decodeValue(valueValue);
                return StaticArrayEntry.of(columnKey, value);
            })
            .filter(entry -> !slice || entry.compareTo(sliceStartEntry) >= 0 && entry.compareTo(sliceEndEntry) < 0)
            .sorted()
            .limit(limit)
            .collect(Collectors.toList());
    }

    public Entry build() {
        if (null == item) {
            return null;
        }

        final StaticBuffer rangeKey = decodeKey(item, Constants.JANUSGRAPH_RANGE_KEY);
        return build(rangeKey);
    }

    public Entry build(final StaticBuffer column) {
        if (null == item || null == column) {
            return null;
        }

        final AttributeValue valueValue = item.get(Constants.JANUSGRAPH_VALUE);
        final StaticBuffer value = decodeValue(valueValue);

        // DynamoDB's between semantics include the end of a slice, but Titan expects the end to be exclusive
        if (slice && column.compareTo(end) == 0) {
            return null;
        }

        return StaticArrayEntry.of(column, value);
    }

    public EntryBuilder slice(final StaticBuffer sliceStart, final StaticBuffer sliceEnd) {
        this.start = sliceStart;
        this.end = sliceEnd;
        this.slice = true;
        return this;
    }

}