/*
 * Copyright (c) 2018, Red Hat, Inc.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.security.krb5.internal;

import java.util.Date;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import sun.security.krb5.PrincipalName;

final class ReferralsCache {

    private static Map<PrincipalName, Map<String, ReferralCacheEntry>> referralsMap =
            new HashMap<>();

    private static final class ReferralCacheEntry {
        private final String toRealm;
        private final Date validUntil;
        ReferralCacheEntry(String toRealm, Date validUntil) {
            this.toRealm = toRealm;
            this.validUntil = validUntil;
        }
        String getToRealm() {
            return toRealm;
        }
        Date getValidUntil() {
            return validUntil;
        }
    }

    static synchronized void put(PrincipalName service,
            String fromRealm, String toRealm, Date validUntil) {
        pruneExpired(service);
        if (validUntil.before(new Date())) {
            return;
        }
        Map<String, ReferralCacheEntry> entries = referralsMap.get(service);
        if (entries == null) {
            entries = new HashMap<String, ReferralCacheEntry>();
            referralsMap.put(service, entries);
        }
        entries.remove(fromRealm);
        ReferralCacheEntry newEntry = new ReferralCacheEntry(toRealm, validUntil);
        entries.put(fromRealm, newEntry);

        // Remove loops within the cache
        ReferralCacheEntry current = newEntry;
        List<ReferralCacheEntry> seen = new LinkedList<>();
        while (current != null) {
            if (seen.contains(current)) {
                // Loop found. Remove the first referral to cut the loop.
                entries.remove(newEntry.getToRealm());
                break;
            }
            seen.add(current);
            current = entries.get(current.getToRealm());
        }
    }

    static synchronized String get(PrincipalName service, String fromRealm) {
        pruneExpired(service);
        Map<String, ReferralCacheEntry> entries = referralsMap.get(service);
        if (entries != null) {
            ReferralCacheEntry toRef = entries.get(fromRealm);
            if (toRef != null) {
                return toRef.getToRealm();
            }
        }
        return null;
    }

    private static void pruneExpired(PrincipalName service) {
        Date now = new Date();
        Map<String, ReferralCacheEntry> entries = referralsMap.get(service);
        if (entries != null) {
            for (Entry<String, ReferralCacheEntry> mapEntry : entries.entrySet()) {
                if (mapEntry.getValue().getValidUntil().before(now)) {
                    entries.remove(mapEntry.getKey());
                }
            }
        }
    }
}