/**
 * 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 com.twitter.distributedlog.client.routing;

import java.net.InetSocketAddress;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;

import com.google.common.collect.ImmutableSet;
import com.twitter.common.base.Command;
import com.twitter.common.base.Commands;
import com.twitter.common.zookeeper.Group;
import com.twitter.common.zookeeper.ServerSet;
import com.twitter.finagle.Addr;
import com.twitter.finagle.Address;
import com.twitter.finagle.Name;
import com.twitter.finagle.Resolver$;
import com.twitter.thrift.Endpoint;
import com.twitter.thrift.ServiceInstance;
import com.twitter.thrift.Status;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import scala.runtime.AbstractFunction1;
import scala.runtime.BoxedUnit;

class NameServerSet implements ServerSet {

    static final Logger logger = LoggerFactory.getLogger(NameServerSet.class);

    private volatile Set<HostChangeMonitor<ServiceInstance>> watchers = new HashSet<HostChangeMonitor<ServiceInstance>>();
    private volatile ImmutableSet<ServiceInstance> hostSet = ImmutableSet.of();
    private AtomicBoolean resolutionPending = new AtomicBoolean(true);

    public NameServerSet(String nameStr) {
        Name name;
        try {
            name = Resolver$.MODULE$.eval(nameStr);
        } catch (Exception exc) {
            logger.error("Exception in Resolver.eval for name {}", nameStr, exc);
            // Since this is called from various places that dont handle specific exceptions,
            // we have no option than to throw a runtime exception to halt the control flow
            // This should only happen in case of incorrect configuration. Having a log message
            // would help identify the problem during tests
            throw new RuntimeException(exc);
        }
        initialize(name);
    }

    public NameServerSet(Name name) {
        initialize(name);
    }

    private void initialize(Name name) {
        if (name instanceof TestName) {
            ((TestName)name).changes(new AbstractFunction1<Addr, BoxedUnit>() {
                @Override
                public BoxedUnit apply(Addr varAddr) {
                    return NameServerSet.this.respondToChanges(varAddr);
                }
            });
        } else if (name instanceof Name.Bound) {
            ((Name.Bound)name).addr().changes().respond(new AbstractFunction1<Addr, BoxedUnit>() {
                @Override
                public BoxedUnit apply(Addr varAddr) {
                    return NameServerSet.this.respondToChanges(varAddr);
                }
            });
        } else {
            logger.error("NameServerSet only supports Name.Bound. While the resolved name {} was {}", name, name.getClass());
            throw new UnsupportedOperationException("NameServerSet only supports Name.Bound");
        }
    }

    private ServiceInstance endpointAddressToServiceInstance(Address endpointAddress) {
        if (endpointAddress instanceof Address.Inet) {
            InetSocketAddress inetSocketAddress = ((Address.Inet) endpointAddress).addr();
            Endpoint endpoint = new Endpoint(inetSocketAddress.getHostString(), inetSocketAddress.getPort());
            HashMap<String, Endpoint> map = new HashMap<String, Endpoint>();
            map.put("thrift", endpoint);
            return new ServiceInstance(
                endpoint,
                map,
                Status.ALIVE);
        } else {
            logger.error("We expect InetSocketAddress while the resolved address {} was {}",
                        endpointAddress, endpointAddress.getClass());
            throw new UnsupportedOperationException("invalid endpoint address: " + endpointAddress);
        }
    }


    private BoxedUnit respondToChanges(Addr addr) {
        ImmutableSet<ServiceInstance> oldHostSet = ImmutableSet.copyOf(hostSet);

        ImmutableSet<ServiceInstance> newHostSet = oldHostSet;

        if (addr instanceof Addr.Bound) {
            scala.collection.immutable.Set<Address> endpointAddresses = ((Addr.Bound)addr).addrs();
            scala.collection.Iterator<Address> endpointAddressesIterator = endpointAddresses.toIterator();
            HashSet<ServiceInstance> serviceInstances = new HashSet<ServiceInstance>();
            while (endpointAddressesIterator.hasNext()) {
                serviceInstances.add(endpointAddressToServiceInstance(endpointAddressesIterator.next()));
            }
            newHostSet = ImmutableSet.copyOf(serviceInstances);

        } else if (addr instanceof Addr.Failed) {
            logger.error("Name resolution failed", ((Addr.Failed)addr).cause());
            newHostSet = ImmutableSet.of();
        } else if (addr.toString().equals("Pending")) {
            logger.info("Name resolution pending");
            newHostSet = oldHostSet;
        } else if (addr.toString().equals("Neg")) {
            newHostSet = ImmutableSet.of();
        } else {
            logger.error("Invalid Addr type: {}", addr.getClass().getName());
            throw new UnsupportedOperationException("Invalid Addr type:" + addr.getClass().getName());
        }

        // Reference comparison is valid as the sets are immutable
        if (oldHostSet != newHostSet) {
            logger.info("NameServerSet updated: {} -> {}", hostSetToString(oldHostSet), hostSetToString(newHostSet));
            resolutionPending.set(false);
            hostSet = newHostSet;
            synchronized (watchers) {
                for (HostChangeMonitor<ServiceInstance> watcher: watchers) {
                    watcher.onChange(newHostSet);
                }
            }

        }

        return BoxedUnit.UNIT;
    }


    private String hostSetToString(ImmutableSet<ServiceInstance> hostSet) {
        StringBuilder result = new StringBuilder();
        result.append("(");
        for (ServiceInstance serviceInstance : hostSet) {
            Endpoint endpoint = serviceInstance.getServiceEndpoint();
            result.append(String.format(" %s:%d", endpoint.getHost(), endpoint.getPort()));
        }
        result.append(" )");

        return result.toString();
    }


    /**
     * Attempts to join a server set for this logical service group.
     *
     * @param endpoint the primary service endpoint
     * @param additionalEndpoints and additional endpoints keyed by their logical name
     * @param status the current service status
     * @return an EndpointStatus object that allows the endpoint to adjust its status
     * @throws Group.JoinException if there was a problem joining the server set
     * @throws InterruptedException if interrupted while waiting to join the server set
     * @deprecated The status field is deprecated. Please use {@link #join(java.net.InetSocketAddress, java.util.Map)}
     */
    @Override
    public EndpointStatus join(InetSocketAddress endpoint, Map<String, InetSocketAddress> additionalEndpoints, Status status)
            throws Group.JoinException, InterruptedException {
        throw new UnsupportedOperationException("NameServerSet does not support join");
    }

    /**
     * Attempts to join a server set for this logical service group.
     *
     * @param endpoint the primary service endpoint
     * @param additionalEndpoints and additional endpoints keyed by their logical name
     * @return an EndpointStatus object that allows the endpoint to adjust its status
     * @throws Group.JoinException if there was a problem joining the server set
     * @throws InterruptedException if interrupted while waiting to join the server set
     */
    @Override
    public EndpointStatus join(InetSocketAddress endpoint, Map<String, InetSocketAddress> additionalEndpoints)
            throws Group.JoinException, InterruptedException {
        throw new UnsupportedOperationException("NameServerSet does not support join");
    }

    /**
     * Attempts to join a server set for this logical service group.
     *
     * @param endpoint the primary service endpoint
     * @param additionalEndpoints and additional endpoints keyed by their logical name
     * @param shardId Unique shard identifier for this member of the service.
     * @return an EndpointStatus object that allows the endpoint to adjust its status
     * @throws Group.JoinException if there was a problem joining the server set
     * @throws InterruptedException if interrupted while waiting to join the server set
     */
    @Override
    public EndpointStatus join(InetSocketAddress endpoint, Map<String, InetSocketAddress> additionalEndpoints, int shardId)
            throws Group.JoinException, InterruptedException {
        throw new UnsupportedOperationException("NameServerSet does not support join");
    }

    /**
     * Registers a monitor to receive change notices for this server set as long as this jvm process
     * is alive.  Blocks until the initial server set can be gathered and delivered to the monitor.
     * The monitor will be notified if the membership set or parameters of existing members have
     * changed.
     *
     * @param monitor the server set monitor to call back when the host set changes
     * @throws com.twitter.common.net.pool.DynamicHostSet.MonitorException if there is a problem monitoring the host set
     * @deprecated Deprecated in favor of {@link #watch(com.twitter.common.net.pool.DynamicHostSet.HostChangeMonitor)}
     */
    @Deprecated
    @Override
    public void monitor(HostChangeMonitor<ServiceInstance> monitor) throws MonitorException {
        throw new UnsupportedOperationException("NameServerSet does not support monitor");
    }

    /**
     * Registers a monitor to receive change notices for this server set as long as this jvm process
     * is alive.  Blocks until the initial server set can be gathered and delivered to the monitor.
     * The monitor will be notified if the membership set or parameters of existing members have
     * changed.
     *
     * @param monitor the server set monitor to call back when the host set changes
     * @return A command which, when executed, will stop monitoring the host set.
     * @throws com.twitter.common.net.pool.DynamicHostSet.MonitorException if there is a problem monitoring the host set
     */
    @Override
    public Command watch(HostChangeMonitor<ServiceInstance> monitor) throws MonitorException {
        // First add the monitor to the watchers so that it does not miss any changes and invoke
        // the onChange method
        synchronized (watchers) {
            watchers.add(monitor);
        }

        if(resolutionPending.compareAndSet(false, false)) {
            monitor.onChange(hostSet);
        }

        return Commands.NOOP; // Return value is not used
    }
}