/**
 * 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.database;

import com.github.zafarkhaja.semver.Version;
import com.mongodb.BasicDBList;
import com.mongodb.CommandResult;
import com.mongodb.DB;
import com.mongodb.Mongo;
import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.MongoCommandException;
import com.mongodb.MongoException;
import com.mongodb.WriteConcern;
import com.mongodb.client.MongoDatabase;
import org.graylog2.configuration.MongoDbConfiguration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nullable;
import javax.inject.Inject;
import javax.inject.Singleton;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Strings.isNullOrEmpty;

/**
 * MongoDB connection singleton
 */
@Singleton
public class MongoConnectionImpl implements MongoConnection {
    private static final Logger LOG = LoggerFactory.getLogger(MongoConnectionImpl.class);
    private static final Version MINIMUM_MONGODB_VERSION = Version.forIntegers(2, 4);

    private final MongoClientURI mongoClientURI;

    private MongoClient m = null;
    private DB db = null;
    private MongoDatabase mongoDatabase = null;

    @Inject
    public MongoConnectionImpl(final MongoDbConfiguration configuration) {
        this(configuration.getMongoClientURI());
    }

    MongoConnectionImpl(MongoClientURI mongoClientURI) {
        this.mongoClientURI = checkNotNull(mongoClientURI);
    }

    /**
     * Connect the instance.
     */
    @Override
    public synchronized Mongo connect() {
        if (m == null) {
            final String dbName = mongoClientURI.getDatabase();
            if (isNullOrEmpty(dbName)) {
                LOG.error("The MongoDB database name must not be null or empty (mongodb_uri was: {})", mongoClientURI);
                throw new RuntimeException("MongoDB database name is missing.");
            }

            m = new MongoClient(mongoClientURI);
            db = m.getDB(dbName);
            db.setWriteConcern(WriteConcern.ACKNOWLEDGED);

            mongoDatabase = m.getDatabase(dbName).withWriteConcern(WriteConcern.ACKNOWLEDGED);
        }

        try {
            db.command("{ ping: 1 }");
        } catch (MongoCommandException e) {
            if (e.getCode() == 18) {
                throw new MongoException("Couldn't connect to MongoDB. Please check the authentication credentials.", e);
            } else {
                throw new MongoException("Couldn't connect to MongoDB: " + e.getMessage(), e);
            }
        }

        final Version mongoVersion = getMongoVersion(m.getDB("admin"));
        if (mongoVersion != null && mongoVersion.lessThan(MINIMUM_MONGODB_VERSION)) {
            LOG.warn("You're running MongoDB {} but Graylog requires at least MongoDB {}. Please upgrade.",
                    mongoVersion, MINIMUM_MONGODB_VERSION);
        }

        return m;
    }

    @Nullable
    private Version getMongoVersion(DB adminDb) {
        final CommandResult buildInfoResult = adminDb.command("buildInfo");
        if (buildInfoResult.ok()) {
            final BasicDBList versionArray = (BasicDBList) buildInfoResult.get("versionArray");
            if (versionArray == null || versionArray.size() < 3) {
                LOG.debug("Couldn't retrieve MongoDB version");
                return null;
            }

            final int majorVersion = (int) versionArray.get(0);
            final int minorVersion = (int) versionArray.get(1);
            final int patchVersion = (int) versionArray.get(2);
            return Version.forIntegers(majorVersion, minorVersion, patchVersion);
        } else {
            LOG.debug("Couldn't retrieve MongoDB buildInfo: {}", buildInfoResult.getErrorMessage());
            return null;
        }
    }

    /**
     * Returns the raw database object.
     *
     * @return database
     */
    @Override
    public DB getDatabase() {
        return db;
    }

    @Override
    public MongoDatabase getMongoDatabase() {
        return mongoDatabase;
    }
}