/*
 * Copyright (c) 2010-2017. Axon Framework
 * 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.
 */

package org.axonframework.eventsourcing.eventstore;

import org.axonframework.eventsourcing.DomainEventMessage;

import java.util.Iterator;

/**
 * DomainEventStream implementation that gets its messages from an Iterator.
 *
 * @since 3.0.3
 */
public class IteratorBackedDomainEventStream implements DomainEventStream {
    private final Iterator<? extends DomainEventMessage<?>> iterator;
    private boolean hasPeeked;
    private DomainEventMessage<?> peekEvent;
    private Long sequenceNumber;

    /**
     * Initialize the stream which provides access to message from the given {@code iterator}
     *
     * @param iterator The iterator providing the messages to stream
     */
    public IteratorBackedDomainEventStream(Iterator<? extends DomainEventMessage<?>> iterator) {
        this.iterator = iterator;
    }

    @Override
    public DomainEventMessage<?> peek() {
        if (!hasPeeked) {
            peekEvent = readNext();
            hasPeeked = true;
        }
        return peekEvent;
    }

    @Override
    public boolean hasNext() {
        return hasPeeked || iterator.hasNext();
    }

    @Override
    public DomainEventMessage<?> next() {
        if (!hasPeeked) {
            return readNext();
        }
        DomainEventMessage<?> result = peekEvent;
        peekEvent = null;
        hasPeeked = false;
        return result;
    }

    private DomainEventMessage<?> readNext() {
        DomainEventMessage<?> next = iterator.next();
        this.sequenceNumber = next.getSequenceNumber();
        return next;
    }

    @Override
    public Long getLastSequenceNumber() {
        return sequenceNumber;
    }
}