/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.zookeeper.server;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import javax.management.JMException;
import javax.security.auth.login.AppConfigurationEntry;
import javax.security.auth.login.Configuration;
import javax.security.auth.login.LoginException;

import org.apache.zookeeper.Environment;
import org.apache.zookeeper.Login;
import org.apache.zookeeper.common.ZKConfig;
import org.apache.zookeeper.jmx.MBeanRegistry;
import org.apache.zookeeper.server.auth.SaslServerCallbackHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public abstract class ServerCnxnFactory {

    public static final String ZOOKEEPER_SERVER_CNXN_FACTORY = "zookeeper.serverCnxnFactory";
    private static final String ZOOKEEPER_MAX_CONNECTION = "zookeeper.maxCnxns";
    public static final int ZOOKEEPER_MAX_CONNECTION_DEFAULT = 0;

    private static final Logger LOG = LoggerFactory.getLogger(ServerCnxnFactory.class);

    // Tells whether SSL is enabled on this ServerCnxnFactory
    protected boolean secure;

    /**
     * The buffer will cause the connection to be close when we do a send.
     */
    static final ByteBuffer closeConn = ByteBuffer.allocate(0);

    // total number of connections accepted by the ZooKeeper server
    protected int maxCnxns;

    // sessionMap is used by closeSession()
    final ConcurrentHashMap<Long, ServerCnxn> sessionMap = new ConcurrentHashMap<Long, ServerCnxn>();

    private static String loginUser = Login.SYSTEM_USER;

    public void addSession(long sessionId, ServerCnxn cnxn) {
        sessionMap.put(sessionId, cnxn);
    }

    public void removeCnxnFromSessionMap(ServerCnxn cnxn) {
        long sessionId = cnxn.getSessionId();
        if(sessionId != 0) {
            sessionMap.remove(sessionId);
        }
    }

    /**
     * @return true if the cnxn that contains the sessionId exists in this ServerCnxnFactory
     * and it's closed. Otherwise false.
     */
    public boolean closeSession(long sessionId, ServerCnxn.DisconnectReason reason) {
        ServerCnxn cnxn = sessionMap.remove(sessionId);
        if(cnxn != null) {
            try {
                cnxn.close(reason);
            } catch(Exception e) {
                LOG.warn("exception during session close", e);
            }
            return true;
        }
        return false;
    }

    public abstract int getLocalPort();

    public abstract Iterable<ServerCnxn> getConnections();

    public int getNumAliveConnections() {
        return cnxns.size();
    }

    public final ZooKeeperServer getZooKeeperServer() {
        return zkServer;
    }

    public void configure(InetSocketAddress addr, int maxcc) throws IOException {
        configure(addr, maxcc, -1);
    }

    public void configure(InetSocketAddress addr, int maxcc, int backlog) throws IOException {
        configure(addr, maxcc, backlog, false);
    }

    public abstract void configure(InetSocketAddress addr, int maxcc, int backlog, boolean secure) throws IOException;

    public abstract void reconfigure(InetSocketAddress addr);

    protected SaslServerCallbackHandler saslServerCallbackHandler;
    public Login login;

    /**
     * Maximum number of connections allowed from particular host (ip)
     */
    public abstract int getMaxClientCnxnsPerHost();

    /**
     * Maximum number of connections allowed from particular host (ip)
     */
    public abstract void setMaxClientCnxnsPerHost(int max);

    public boolean isSecure() {
        return secure;
    }

    public void startup(ZooKeeperServer zkServer) throws IOException, InterruptedException {
        startup(zkServer, true);
    }

    // This method is to maintain compatiblity of startup(zks) and enable sharing of zks
    // when we add secureCnxnFactory.
    public abstract void startup(ZooKeeperServer zkServer, boolean startServer) throws IOException, InterruptedException;

    /**
     * The maximum queue length of the ZooKeeper server's socket
     */
    public abstract int getSocketListenBacklog();

    public abstract void join() throws InterruptedException;

    public abstract void shutdown();

    public abstract void start();

    protected ZooKeeperServer zkServer;

    public final void setZooKeeperServer(ZooKeeperServer zks) {
        this.zkServer = zks;
        if(zks != null) {
            if(secure) {
                zks.setSecureServerCnxnFactory(this);
            } else {
                zks.setServerCnxnFactory(this);
            }
        }
    }

    public abstract void closeAll(ServerCnxn.DisconnectReason reason);

    public static ServerCnxnFactory createFactory() throws IOException {

        // TODO_MA 注释： 从环境变量中，找到 zookeeper.serverCnxnFactory 对应的 value 一般是么有配置的
        // TODO_MA 注释： 如果需要更改，则： zookeeper.serverCnxnFactory = org.apache.zookeeper.server.NettyServerCnxnFactory
        // TODO_MA 马中华 注释： 默认实现：NIOServerCnxnFactory
        String serverCnxnFactoryName = System.getProperty(ZOOKEEPER_SERVER_CNXN_FACTORY);
        if(serverCnxnFactoryName == null) {
            serverCnxnFactoryName = NIOServerCnxnFactory.class.getName();
        }

        // TODO_MA 注释： 通过反射来创建一个 实例对象
        try {
            ServerCnxnFactory serverCnxnFactory = (ServerCnxnFactory) Class.forName(serverCnxnFactoryName)
                    .getDeclaredConstructor().newInstance();
            LOG.info("Using {} as server connection factory", serverCnxnFactoryName);
            return serverCnxnFactory;
        } catch(Exception e) {
            IOException ioe = new IOException("Couldn't instantiate " + serverCnxnFactoryName, e);
            throw ioe;
        }
    }

    public static ServerCnxnFactory createFactory(int clientPort, int maxClientCnxns) throws IOException {
        return createFactory(new InetSocketAddress(clientPort), maxClientCnxns, -1);
    }

    public static ServerCnxnFactory createFactory(int clientPort, int maxClientCnxns, int backlog) throws IOException {
        return createFactory(new InetSocketAddress(clientPort), maxClientCnxns, backlog);
    }

    public static ServerCnxnFactory createFactory(InetSocketAddress addr, int maxClientCnxns) throws IOException {
        return createFactory(addr, maxClientCnxns, -1);
    }

    public static ServerCnxnFactory createFactory(InetSocketAddress addr, int maxClientCnxns,
            int backlog) throws IOException {
        ServerCnxnFactory factory = createFactory();
        factory.configure(addr, maxClientCnxns, backlog);
        return factory;
    }

    public abstract InetSocketAddress getLocalAddress();

    public abstract void resetAllConnectionStats();

    public abstract Iterable<Map<String, Object>> getAllConnectionInfo(boolean brief);

    private final ConcurrentHashMap<ServerCnxn, ConnectionBean> connectionBeans = new ConcurrentHashMap<ServerCnxn, ConnectionBean>();

    // Connection set is relied on heavily by four letter commands
    // Construct a ConcurrentHashSet using a ConcurrentHashMap
    protected final Set<ServerCnxn> cnxns = Collections.newSetFromMap(new ConcurrentHashMap<ServerCnxn, Boolean>());

    public void unregisterConnection(ServerCnxn serverCnxn) {
        ConnectionBean jmxConnectionBean = connectionBeans.remove(serverCnxn);
        if(jmxConnectionBean != null) {
            MBeanRegistry.getInstance().unregister(jmxConnectionBean);
        }
    }

    public void registerConnection(ServerCnxn serverCnxn) {
        if(zkServer != null) {
            ConnectionBean jmxConnectionBean = new ConnectionBean(serverCnxn, zkServer);
            try {
                MBeanRegistry.getInstance().register(jmxConnectionBean, zkServer.jmxServerBean);
                connectionBeans.put(serverCnxn, jmxConnectionBean);
            } catch(JMException e) {
                LOG.warn("Could not register connection", e);
            }
        }

    }

    /**
     * Initialize the server SASL if specified.
     *
     * If the user has specified a "ZooKeeperServer.LOGIN_CONTEXT_NAME_KEY"
     * or a jaas.conf using "java.security.auth.login.config"
     * the authentication is required and an exception is raised.
     * Otherwise no authentication is configured and no exception is raised.
     *
     * @throws IOException if jaas.conf is missing or there's an error in it.
     */
    protected void configureSaslLogin() throws IOException {
        String serverSection = System
                .getProperty(ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY, ZooKeeperSaslServer.DEFAULT_LOGIN_CONTEXT_NAME);

        // Note that 'Configuration' here refers to javax.security.auth.login.Configuration.
        AppConfigurationEntry[] entries = null;
        SecurityException securityException = null;
        try {
            entries = Configuration.getConfiguration().getAppConfigurationEntry(serverSection);
        } catch(SecurityException e) {
            // handle below: might be harmless if the user doesn't intend to use JAAS authentication.
            securityException = e;
        }

        // No entries in jaas.conf
        // If there's a configuration exception fetching the jaas section and
        // the user has required sasl by specifying a LOGIN_CONTEXT_NAME_KEY or a jaas file
        // we throw an exception otherwise we continue without authentication.
        if(entries == null) {
            String jaasFile = System.getProperty(Environment.JAAS_CONF_KEY);
            String loginContextName = System.getProperty(ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY);
            if(securityException != null && (loginContextName != null || jaasFile != null)) {
                String errorMessage = "No JAAS configuration section named '" + serverSection + "' was found";
                if(jaasFile != null) {
                    errorMessage += " in '" + jaasFile + "'.";
                }
                if(loginContextName != null) {
                    errorMessage += " But " + ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY + " was set.";
                }
                LOG.error(errorMessage);
                throw new IOException(errorMessage);
            }
            return;
        }

        // jaas.conf entry available
        try {
            saslServerCallbackHandler = new SaslServerCallbackHandler(Configuration.getConfiguration());
            login = new Login(serverSection, saslServerCallbackHandler, new ZKConfig());
            setLoginUser(login.getUserName());
            login.startThreadIfNeeded();
        } catch(LoginException e) {
            throw new IOException(
                    "Could not configure server because SASL configuration did not allow the " + " ZooKeeper server to authenticate itself properly: " + e);
        }
    }

    private static void setLoginUser(String name) {
        //Created this method to avoid ST_WRITE_TO_STATIC_FROM_INSTANCE_METHOD find bug issue
        loginUser = name;
    }

    /**
     * User who has started the ZooKeeper server user, it will be the logged-in
     * user. If no user logged-in then system user
     */
    public static String getUserName() {
        return loginUser;
    }

    /**
     * Maximum number of connections allowed in the ZooKeeper system
     */
    public int getMaxCnxns() {
        return maxCnxns;
    }

    protected void initMaxCnxns() {
        maxCnxns = Integer.getInteger(ZOOKEEPER_MAX_CONNECTION, ZOOKEEPER_MAX_CONNECTION_DEFAULT);
        if(maxCnxns < 0) {
            maxCnxns = ZOOKEEPER_MAX_CONNECTION_DEFAULT;
            LOG.warn("maxCnxns should be greater than or equal to 0, using default vlaue {}.",
                    ZOOKEEPER_MAX_CONNECTION_DEFAULT);
        } else if(maxCnxns == ZOOKEEPER_MAX_CONNECTION_DEFAULT) {
            LOG.warn("maxCnxns is not configured, using default value {}.", ZOOKEEPER_MAX_CONNECTION_DEFAULT);
        } else {
            LOG.info("maxCnxns configured value is {}.", maxCnxns);
        }
    }

    /**
     * Ensure total number of connections are less than the maxCnxns
     */
    protected boolean limitTotalNumberOfCnxns() {
        if(maxCnxns <= 0) {
            // maxCnxns limit is disabled
            return false;
        }
        int cnxns = getNumAliveConnections();
        if(cnxns >= maxCnxns) {
            LOG.error("Too many connections " + cnxns + " - max is " + maxCnxns);
            return true;
        }
        return false;
    }
}
