/*
 * 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.distributedlog;

import com.twitter.util.Future;
import java.util.List;
import java.util.concurrent.TimeUnit;

/**
 * A log reader to read records in asynchronous way.
 */
public interface AsyncLogReader {

    /**
     * Get stream name that the reader reads from.
     *
     * @return stream name.
     */
    String getStreamName();

    /**
     * Read the next record from the log stream.
     *
     * @return A promise that when satisfied will contain the Log Record with its DLSN.
     */
    Future<LogRecordWithDLSN> readNext();

    /**
     * Read next <i>numEntries</i> entries. The future is only satisfied with non-empty list
     * of entries. It doesn't block until returning exact <i>numEntries</i>. It is a best effort
     * call.
     *
     * @param numEntries
     *          num entries
     * @return A promise that when satisfied will contain a non-empty list of records with their DLSN.
     */
    Future<List<LogRecordWithDLSN>> readBulk(int numEntries);

    /**
     * Read next <i>numEntries</i> entries in a given <i>waitTime</i>.
     *
     * <p>The future is satisfied when either reads <i>numEntries</i> entries or reaches <i>waitTime</i>.
     * The only exception is if there isn't any new entries written within <i>waitTime</i>, it would
     * wait until new entries are available.
     *
     * @param numEntries
     *          max entries to return
     * @param waitTime
     *          maximum wait time if there are entries already for read
     * @param timeUnit
     *          wait time unit
     * @return A promise that when satisfied will contain a non-empty list of records with their DLSN.
     */
    Future<List<LogRecordWithDLSN>> readBulk(int numEntries, long waitTime, TimeUnit timeUnit);

    /**
     * Closes this source and releases any system resources associated
     * with it. If the source is already closed then invoking this
     * method has no effect.
     *
     * @return future representing the close result.
     */
    Future<Void> asyncClose();
}