server/extensions/xep0313-mam/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0313_mam/in_memory/InMemoryArchivedMessagesLastPage.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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.
 *  
 */
package org.apache.vysper.xmpp.modules.extension.xep0313_mam.in_memory;

import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

import org.apache.vysper.xmpp.modules.extension.xep0313_mam.spi.ArchivedMessage;
import org.apache.vysper.xmpp.modules.extension.xep0313_mam.spi.ArchivedMessages;

/**
 * @author Réda Housni Alaoui
 */
public class InMemoryArchivedMessagesLastPage implements ArchivedMessages {

    private final List<ArchivedMessage> list;

    private final Long firstMessageIndex;

    private final long totalNumberOfMessages;

    public InMemoryArchivedMessagesLastPage(long pageSize, List<ArchivedMessage> unlimitedMessages) {
        totalNumberOfMessages = unlimitedMessages.size();
        this.firstMessageIndex = totalNumberOfMessages - Math.min(totalNumberOfMessages, pageSize);
        this.list = unlimitedMessages.stream().skip(firstMessageIndex).collect(Collectors.toList());
    }

    @Override
    public List<ArchivedMessage> list() {
        return list;
    }

    @Override
    public boolean isEmpty() {
        return list.isEmpty();
    }

    @Override
    public boolean isComplete() {
        return list.size() == totalNumberOfMessages;
    }

    @Override
    public Optional<Long> firstMessageIndex() {
        return Optional.ofNullable(firstMessageIndex);
    }

    @Override
    public Optional<Long> totalNumberOfMessages() {
        return Optional.of(totalNumberOfMessages);
    }
}