/**
 * This file is part of Graylog.
 *
 * Graylog 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.
 *
 * Graylog 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 Graylog.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.graylog2.security;

import com.google.common.collect.ImmutableList;
import com.google.common.eventbus.EventBus;
import com.google.common.eventbus.Subscribe;
import org.apache.shiro.realm.AuthenticatingRealm;
import org.apache.shiro.realm.Realm;
import org.graylog2.cluster.ClusterConfigChangedEvent;
import org.graylog2.plugin.cluster.ClusterConfigService;
import org.graylog2.utilities.LenientExplicitOrdering;

import javax.annotation.Nonnull;
import javax.inject.Inject;
import java.util.AbstractCollection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Collectors;

/**
 * Runtime (re-)orderable collection of Shiro AuthenticatingRealms.
 *
 * The generic type is Realm, even though it really only contains AuthenticatingRealms. This is simply to avoid having to
 * cast the generic collection when passing it to the SecurityManager.
 */
public class OrderedAuthenticatingRealms extends AbstractCollection<Realm> {

    private final Map<String, AuthenticatingRealm> availableRealms;
    private final ClusterConfigService clusterConfigService;

    private final AtomicReference<List<Realm>> orderedRealms = new AtomicReference<>();

    @Inject
    public OrderedAuthenticatingRealms(Map<String, AuthenticatingRealm> realms,
                                       ClusterConfigService clusterConfigService,
                                       EventBus eventBus) {
        this.availableRealms = realms;
        this.clusterConfigService = clusterConfigService;
        eventBus.register(this);

        sortRealms();
        // sortRealms should have produced a reasonable default
        Objects.requireNonNull(orderedRealms.get());
    }

    @Subscribe
    public void handleOrderingUpdate(ClusterConfigChangedEvent event) {
        if (!AuthenticationConfig.class.getCanonicalName().equals(event.type())) {
            return;
        }

        sortRealms();
    }

    private void sortRealms() {
        final AuthenticationConfig config = clusterConfigService.getOrDefault(AuthenticationConfig.class,
                                                                              AuthenticationConfig.defaultInstance());

        final LenientExplicitOrdering<String> ordering = new LenientExplicitOrdering<>(config.realmOrder());

        final ImmutableList<String> newRealmOrder = ordering.immutableSortedCopy(availableRealms.keySet());
        orderedRealms.set(newRealmOrder.stream()
                                  .filter(name -> !config.disabledRealms().contains(name))
                                  .map(availableRealms::get)
                                  .collect(Collectors.toList()));
    }

    @Nonnull
    @Override
    public Iterator<Realm> iterator() {
        return orderedRealms.get().iterator();
    }

    @Override
    public int size() {
        return orderedRealms.get().size();
    }
}