ReftableReflogReader.java

/*
 * Copyright (C) 2019, Google LLC and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.reftable;

import org.eclipse.jgit.lib.ReflogEntry;
import org.eclipse.jgit.lib.ReflogReader;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;

/**
 * Implement the ReflogReader interface for a reflog stored in reftable.
 */
public class ReftableReflogReader implements ReflogReader {
    private final Lock lock;

    private final Reftable reftable;

    private final String refname;

    ReftableReflogReader(Lock lock, Reftable merged, String refname) {
        this.lock = lock;
        this.reftable = merged;
        this.refname = refname;
    }

    /** {@inheritDoc} */
    @Override
    public ReflogEntry getLastEntry() throws IOException {
        lock.lock();
        try {
            LogCursor cursor = reftable.seekLog(refname);
            return cursor.next() ? cursor.getReflogEntry() : null;
        } finally {
            lock.unlock();
        }
    }

    /** {@inheritDoc} */
    @Override
    public List<ReflogEntry> getReverseEntries() throws IOException {
        return getReverseEntries(Integer.MAX_VALUE);
    }

    /** {@inheritDoc} */
    @Override
    public ReflogEntry getReverseEntry(int number) throws IOException {
        lock.lock();
        try {
            LogCursor cursor = reftable.seekLog(refname);
            while (true) {
                if (!cursor.next() || number < 0) {
                    return null;
                }
                if (number == 0) {
                    return cursor.getReflogEntry();
                }
                number--;
            }
        } finally {
            lock.unlock();
        }
    }

    /** {@inheritDoc} */
    @Override
    public List<ReflogEntry> getReverseEntries(int max) throws IOException {
        lock.lock();
        try {
            LogCursor cursor = reftable.seekLog(refname);

            List<ReflogEntry> result = new ArrayList<>();
            while (cursor.next() && result.size() < max) {
                result.add(cursor.getReflogEntry());
            }

            return result;
        } finally {
            lock.unlock();
        }
    }
}