InstantComparator.java

/*
 * Copyright (C) 2019, Thomas Wolf <thomas.wolf@paranor.ch> 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.treewalk;

import java.time.Instant;
import java.util.Comparator;

/**
 * Specialized comparator for {@link Instant}s. If either timestamp has a zero
 * fraction, compares only seconds. If either timestamp has no time fraction
 * smaller than a millisecond, compares only milliseconds. If either timestamp
 * has no fraction smaller than a microsecond, compares only microseconds.
 */
class InstantComparator implements Comparator<Instant> {

    @Override
    public int compare(Instant a, Instant b) {
        return compare(a, b, false);
    }

    /**
     * Compares two {@link Instant}s to the lower resolution of the two
     * instants. See {@link InstantComparator}.
     *
     * @param a
     *            first {@link Instant} to compare
     * @param b
     *            second {@link Instant} to compare
     * @param forceSecondsOnly
     *            whether to omit all fraction comparison
     * @return a value &lt; 0 if a &lt; b, a value &gt; 0 if a &gt; b, and 0 if
     *         a == b
     */
    public int compare(Instant a, Instant b, boolean forceSecondsOnly) {
        long aSeconds = a.getEpochSecond();
        long bSeconds = b.getEpochSecond();
        int result = Long.compare(aSeconds, bSeconds);
        if (result != 0) {
            return result;
        }
        int aSubSecond = a.getNano();
        int bSubSecond = b.getNano();
        if (forceSecondsOnly || (aSubSecond == 0)
                || (bSubSecond == 0)) {
            // Don't check the subseconds part.
            return 0;
        } else if (aSubSecond != bSubSecond) {
            // If either has nothing smaller than a millisecond, compare only
            // milliseconds.
            int aSubMillis = aSubSecond % 1_000_000;
            int bSubMillis = bSubSecond % 1_000_000;
            if (aSubMillis == 0) {
                bSubSecond -= bSubMillis;
            } else if (bSubMillis == 0) {
                aSubSecond -= aSubMillis;
            } else {
                // Same again, but for microsecond resolution. NTFS has 100ns
                // resolution, but WindowsFileAttributes may provide only
                // microseconds (1000ns). Similar for some Unix file systems.
                int aSubMicros = aSubSecond % 1000;
                int bSubMicros = bSubSecond % 1000;
                if (aSubMicros == 0) {
                    bSubSecond -= bSubMicros;
                } else if (bSubMicros == 0) {
                    aSubSecond -= aSubMicros;
                }
            }
        }
        return Integer.compare(aSubSecond, bSubSecond);
    }

}