/*
 * 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 com.addthis.hydra.task.source;

import javax.annotation.Nullable;

import com.addthis.bundle.core.Bundle;
import com.addthis.bundle.core.list.ListBundle;
import com.addthis.codec.annotations.FieldConfig;

import com.google.common.base.Preconditions;

/**
 * This data source <span class="hydra-summary">creates an arbitrary number of empty bundles</span>.
 * <p/>
 * <p>The maxPackets parameter determines how many bundles are created. The default
 * value of maxPackets (-1) indicates that an infinite number of bundles are created.
 *
 * @user-reference
 */
public class DataSourceEmpty extends TaskDataSource {

    /**
     * Number of bundles that will be created.
     * Default is -1 which creates an infinite number of bundles.
     */
    @FieldConfig private long maxPackets = -1; // go forever

    private volatile boolean closed = false;

    private long packetsCreated = 0;

    private Bundle next;

    private static ListBundle createBundle() {
        return new ListBundle();
    }

    @Override public void init() {
        generateNext();
    }

    private void generateNext() {
        Preconditions.checkState(next == null);
        if (!closed
            && ((maxPackets < 0) || (packetsCreated < maxPackets))) {
            next = createBundle();
            packetsCreated++;
        }
    }

    @Nullable
    @Override
    public Bundle peek() {
        return next;
    }

    @Override public Bundle next() {
        Bundle result = next;
        next = null;
        generateNext();
        return result;
    }

    @Override public void close() {
        closed = true;
    }
}