/*
 * 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.internal.id.indexed;

import java.util.function.Consumer;
import java.util.function.LongSupplier;
import org.neo4j.index.internal.gbptree.GBPTree;
import org.neo4j.io.pagecache.PageCursor;
import org.neo4j.io.pagecache.context.CursorContext;

/**
 * Writes header of an {@link IndexedIdGenerator} into the {@link GBPTree}.
 *
 * @see HeaderReader
 */
class HeaderWriter implements Consumer<PageCursor> {
    /**
     * highId to write in the header. This is a supplier because of how this writer is constructed before entering the critical
     * section inside {@link GBPTree#checkpoint(CursorContext)} and so the highId may have changed between constructing this writer
     * and entering the checkpoint critical section.
     */
    private final LongSupplier highId;

    private final LongSupplier highestWrittenId;
    private final long generation;
    private final int idsPerEntry;

    HeaderWriter(LongSupplier highId, LongSupplier highestWrittenId, long generation, int idsPerEntry) {
        this.highId = highId;
        this.highestWrittenId = highestWrittenId;
        this.generation = generation;
        this.idsPerEntry = idsPerEntry;
    }

    @Override
    public void accept(PageCursor cursor) {
        long highId = this.highId.getAsLong();
        long highestWrittenId = this.highestWrittenId.getAsLong();
        cursor.putLong(highId);
        cursor.putLong(highestWrittenId);
        cursor.putLong(generation);
        cursor.putInt(idsPerEntry);
    }
}
