/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.kernel.impl.api;

/**
 * Serves as a reusable utility for building a chain of {@link TransactionToApply} instances,
 * where the instances themselves form the linked list. This utility is just for easily being able
 * to append to the end and then at regular intervals batch through the whole queue.
 */
public class TransactionQueue {
    @FunctionalInterface
    public interface Applier {
        void apply(TransactionToApply tx) throws Exception;
    }

    private final int maxSize;
    private final Applier applier;
    private TransactionToApply tail;
    private TransactionToApply head;
    private int size;

    public TransactionQueue(int maxSize, Applier applier) {
        this.maxSize = maxSize;
        this.applier = applier;
    }

    public void queue(TransactionToApply transaction) throws Exception {
        if (isNotEmpty()) {
            tail.next(transaction);
        } else {
            head = transaction;
        }
        tail = transaction;
        if (++size == maxSize) {
            applyTransactions();
        }
    }

    public void applyTransactions() throws Exception {
        if (isNotEmpty()) {
            applier.apply(head);
            tail = null;
            head = null;
            size = 0;
        }
    }

    private boolean isNotEmpty() {
        return size != 0;
    }
}
