/*
 * Copyright 2016-present Open Networking Foundation
 *
 * Licensed 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.opencord.cordvtn.impl;

import com.google.common.base.Strings;
import com.google.common.collect.Lists;
import com.google.common.primitives.Bytes;
import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Modified;
import org.apache.felix.scr.annotations.Property;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.ReferenceCardinality;
import org.onlab.packet.DHCP;
import org.onlab.packet.Ethernet;
import org.onlab.packet.IPv4;
import org.onlab.packet.Ip4Address;
import org.onlab.packet.IpPrefix;
import org.onlab.packet.MacAddress;
import org.onlab.packet.TpPort;
import org.onlab.packet.UDP;
import org.onlab.packet.dhcp.DhcpOption;
import org.onlab.util.Tools;
import org.onosproject.cfg.ComponentConfigService;
import org.onosproject.core.ApplicationId;
import org.onosproject.core.CoreService;
import org.onosproject.net.ConnectPoint;
import org.onosproject.net.Host;
import org.onosproject.net.HostId;
import org.onosproject.net.flow.DefaultTrafficSelector;
import org.onosproject.net.flow.DefaultTrafficTreatment;
import org.onosproject.net.flow.TrafficSelector;
import org.onosproject.net.flow.TrafficTreatment;
import org.onosproject.net.host.HostService;
import org.onosproject.net.packet.DefaultOutboundPacket;
import org.onosproject.net.packet.PacketContext;
import org.onosproject.net.packet.PacketPriority;
import org.onosproject.net.packet.PacketProcessor;
import org.onosproject.net.packet.PacketService;
import org.opencord.cordvtn.api.Constants;
import org.opencord.cordvtn.api.core.Instance;
import org.opencord.cordvtn.api.core.ServiceNetworkService;
import org.opencord.cordvtn.api.net.NetworkId;
import org.opencord.cordvtn.api.net.ServiceNetwork;
import org.osgi.service.component.ComponentContext;
import org.slf4j.Logger;

import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.Dictionary;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.stream.Collectors;

import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_BroadcastAddress;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_DHCPServerIp;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_DomainServer;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_END;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_LeaseTime;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_MessageType;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_RouterAddress;
import static org.onlab.packet.DHCP.DHCPOptionCode.OptionCode_SubnetMask;
import static org.onlab.packet.DHCPPacketType.DHCPACK;
import static org.onlab.packet.DHCPPacketType.DHCPOFFER;
import static org.opencord.cordvtn.api.Constants.DEFAULT_GATEWAY_MAC_STR;
import static org.opencord.cordvtn.api.net.ServiceNetwork.DependencyType.BIDIRECTIONAL;
import static org.opencord.cordvtn.api.net.ServiceNetwork.NetworkType.MANAGEMENT_HOST;
import static org.opencord.cordvtn.api.net.ServiceNetwork.NetworkType.MANAGEMENT_LOCAL;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Handles DHCP requests for the virtual instances.
 */
@Component(immediate = true)
public class CordVtnDhcpProxy {

    protected final Logger log = getLogger(getClass());

    private static final String DHCP_SERVER_MAC = "dhcpServerMac";

    private static final byte DHCP_OPTION_MTU = (byte) 26;
    private static final byte DHCP_OPTION_CLASSLESS_STATIC_ROUTE = (byte) 121;

    private static final Ip4Address DEFAULT_DNS = Ip4Address.valueOf("8.8.8.8");
    private static final Ip4Address IP_BROADCAST = Ip4Address.valueOf("255.255.255.255");
    private static final byte DEFAULT_PACKET_TTL = (byte) 127;
    private static final byte[] DHCP_DATA_LEASE_INFINITE =
            ByteBuffer.allocate(4).putInt(-1).array();
    private static final byte[] DHCP_DATA_MTU_DEFAULT =
            ByteBuffer.allocate(2).putShort((short) 1450).array();

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected CoreService coreService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ComponentConfigService configService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected PacketService packetService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected HostService hostService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ServiceNetworkService snetService;

    @Property(name = DHCP_SERVER_MAC, value = DEFAULT_GATEWAY_MAC_STR,
            label = "Fake MAC address for DHCP server interface")
    private String dhcpServerMac = DEFAULT_GATEWAY_MAC_STR;

    private final PacketProcessor packetProcessor = new InternalPacketProcessor();

    private ApplicationId appId;

    @Activate
    protected void activate() {
        appId = coreService.registerApplication(Constants.CORDVTN_APP_ID);
        configService.registerProperties(getClass());
        packetService.addProcessor(packetProcessor, PacketProcessor.director(0));
        requestPackets();

        log.info("Started");
    }

    @Deactivate
    protected void deactivate() {
        packetService.removeProcessor(packetProcessor);
        configService.unregisterProperties(getClass(), false);
        cancelPackets();

        log.info("Stopped");
    }

    @Modified
    protected void modified(ComponentContext context) {
        Dictionary<?, ?> properties = context.getProperties();
        String updatedMac;

        updatedMac = Tools.get(properties, DHCP_SERVER_MAC);
        if (!Strings.isNullOrEmpty(updatedMac) && !updatedMac.equals(dhcpServerMac)) {
            dhcpServerMac = updatedMac;
        }

        log.info("Modified");
    }

    private void requestPackets() {
        TrafficSelector selector = DefaultTrafficSelector.builder()
                .matchEthType(Ethernet.TYPE_IPV4)
                .matchIPProtocol(IPv4.PROTOCOL_UDP)
                .matchUdpDst(TpPort.tpPort(UDP.DHCP_SERVER_PORT))
                .matchUdpSrc(TpPort.tpPort(UDP.DHCP_CLIENT_PORT))
                .build();
        packetService.requestPackets(selector, PacketPriority.CONTROL, appId);
    }

    private void cancelPackets() {
        TrafficSelector selector = DefaultTrafficSelector.builder()
                .matchEthType(Ethernet.TYPE_IPV4)
                .matchIPProtocol(IPv4.PROTOCOL_UDP)
                .matchUdpDst(TpPort.tpPort(UDP.DHCP_SERVER_PORT))
                .matchUdpSrc(TpPort.tpPort(UDP.DHCP_CLIENT_PORT))
                .build();
        packetService.cancelPackets(selector, PacketPriority.CONTROL, appId);
    }

    private class InternalPacketProcessor implements PacketProcessor {

        @Override
        public void process(PacketContext context) {
            if (context.isHandled()) {
                return;
            }

            Ethernet ethPacket = context.inPacket().parsed();
            if (ethPacket == null || ethPacket.getEtherType() != Ethernet.TYPE_IPV4) {
                return;
            }

            IPv4 ipv4Packet = (IPv4) ethPacket.getPayload();
            if (ipv4Packet.getProtocol() != IPv4.PROTOCOL_UDP) {
                return;
            }

            UDP udpPacket = (UDP) ipv4Packet.getPayload();
            if (udpPacket.getDestinationPort() != UDP.DHCP_SERVER_PORT ||
                    udpPacket.getSourcePort() != UDP.DHCP_CLIENT_PORT) {
                return;
            }

            DHCP dhcpPacket = (DHCP) udpPacket.getPayload();
            processDhcp(context, dhcpPacket);
        }

        private void processDhcp(PacketContext context, DHCP dhcpPacket) {
            if (dhcpPacket == null) {
                log.trace("DHCP packet without payload received, do nothing");
                return;
            }

            DHCP.MsgType inPacketType = dhcpPacket.getPacketType();
            if (inPacketType == null || dhcpPacket.getClientHardwareAddress() == null) {
                log.trace("Malformed DHCP packet received, ignore it");
                return;
            }

            MacAddress clientMac = MacAddress.valueOf(dhcpPacket.getClientHardwareAddress());
            Host reqHost = hostService.getHost(HostId.hostId(clientMac));
            if (reqHost == null) {
                log.debug("DHCP packet from unknown host, ignore it");
                return;
            }

            Instance reqInstance = Instance.of(reqHost);
            Ethernet ethPacket = context.inPacket().parsed();
            switch (inPacketType) {
                case DHCPDISCOVER:
                    log.trace("DHCP DISCOVER received from {}", reqHost.id());
                    Ethernet discoverReply = buildReply(
                            ethPacket,
                            (byte) DHCPOFFER.getValue(),
                            reqInstance);
                    sendReply(context, discoverReply);
                    log.trace("DHCP OFFER({}) is sent to {}",
                              reqInstance.ipAddress(), reqHost.id());
                    break;
                case DHCPREQUEST:
                    log.trace("DHCP REQUEST received from {}", reqHost.id());
                    Ethernet requestReply = buildReply(
                            ethPacket,
                            (byte) DHCPACK.getValue(),
                            reqInstance);
                    sendReply(context, requestReply);
                    log.trace("DHCP ACK({}) is sent to {}",
                              reqInstance.ipAddress(), reqHost.id());
                    break;
                case DHCPRELEASE:
                    log.trace("DHCP RELEASE received from {}", reqHost.id());
                    // do nothing
                    break;
                default:
                    log.warn("Unknown packet type {}", inPacketType);
                    break;
            }
        }

        private Ethernet buildReply(Ethernet ethRequest, byte packetType,
                                    Instance reqInstance) {
            ServiceNetwork snet = snetService.serviceNetwork(reqInstance.netId());
            Ip4Address serverIp = snet.serviceIp().getIp4Address();

            Ethernet ethReply = new Ethernet();
            ethReply.setSourceMACAddress(dhcpServerMac);
            ethReply.setDestinationMACAddress(ethRequest.getSourceMAC());
            ethReply.setEtherType(Ethernet.TYPE_IPV4);

            IPv4 ipv4Request = (IPv4) ethRequest.getPayload();
            IPv4 ipv4Reply = new IPv4();
            ipv4Reply.setSourceAddress(serverIp.toInt());
            ipv4Reply.setDestinationAddress(reqInstance.ipAddress().toInt());
            ipv4Reply.setTtl(DEFAULT_PACKET_TTL);

            UDP udpRequest = (UDP) ipv4Request.getPayload();
            UDP udpReply = new UDP();
            udpReply.setSourcePort((byte) UDP.DHCP_SERVER_PORT);
            udpReply.setDestinationPort((byte) UDP.DHCP_CLIENT_PORT);

            DHCP dhcpRequest = (DHCP) udpRequest.getPayload();
            DHCP dhcpReply = buildDhcpReply(
                    dhcpRequest, packetType, reqInstance.ipAddress(), snet);

           // Overwrite the DstIP and DstMac if broadcast flag is set in DHCP header.
           // This Fix alligns the ONOS-VTN app with the DHCP RFC
            if ((dhcpRequest.getFlags() & 0x8000) != 0) {
                ipv4Reply.setDestinationAddress(IP_BROADCAST.toInt());
                ethReply.setDestinationMACAddress(MacAddress.BROADCAST);
            }
           // End of DHCP Fix.

            udpReply.setPayload(dhcpReply);
            ipv4Reply.setPayload(udpReply);
            ethReply.setPayload(ipv4Reply);

            return ethReply;
        }

        private void sendReply(PacketContext context, Ethernet ethReply) {
            if (ethReply == null) {
                return;
            }
            ConnectPoint srcPoint = context.inPacket().receivedFrom();
            TrafficTreatment treatment = DefaultTrafficTreatment
                    .builder()
                    .setOutput(srcPoint.port())
                    .build();

            packetService.emit(new DefaultOutboundPacket(
                    srcPoint.deviceId(),
                    treatment,
                    ByteBuffer.wrap(ethReply.serialize())));
            context.block();
        }

        private DHCP buildDhcpReply(DHCP request, byte msgType, Ip4Address yourIp,
                                    ServiceNetwork snet) {
            Ip4Address serverIp = snet.serviceIp().getIp4Address();
            int subnetPrefixLen = snet.subnet().prefixLength();

            DHCP dhcpReply = new DHCP();
            dhcpReply.setOpCode(DHCP.OPCODE_REPLY);
            dhcpReply.setHardwareType(DHCP.HWTYPE_ETHERNET);
            dhcpReply.setHardwareAddressLength((byte) 6);
            dhcpReply.setTransactionId(request.getTransactionId());
            dhcpReply.setFlags(request.getFlags());
            dhcpReply.setServerIPAddress(serverIp.toInt());
            dhcpReply.setYourIPAddress(yourIp.toInt());
            dhcpReply.setClientHardwareAddress(request.getClientHardwareAddress());

            List<DhcpOption> options = Lists.newArrayList();
            // message type
            DhcpOption option = new DhcpOption();
            option.setCode(OptionCode_MessageType.getValue());
            option.setLength((byte) 1);
            byte[] optionData = {msgType};
            option.setData(optionData);
            options.add(option);

            // server identifier
            option = new DhcpOption();
            option.setCode(OptionCode_DHCPServerIp.getValue());
            option.setLength((byte) 4);
            option.setData(serverIp.toOctets());
            options.add(option);

            // lease time
            option = new DhcpOption();
            option.setCode(OptionCode_LeaseTime.getValue());
            option.setLength((byte) 4);
            option.setData(DHCP_DATA_LEASE_INFINITE);
            options.add(option);

            // subnet mask
            Ip4Address subnetMask = Ip4Address.makeMaskPrefix(subnetPrefixLen);
            option = new DhcpOption();
            option.setCode(OptionCode_SubnetMask.getValue());
            option.setLength((byte) 4);
            option.setData(subnetMask.toOctets());
            options.add(option);

            // broadcast address
            Ip4Address broadcast = Ip4Address.makeMaskedAddress(yourIp, subnetPrefixLen);
            option = new DhcpOption();
            option.setCode(OptionCode_BroadcastAddress.getValue());
            option.setLength((byte) 4);
            option.setData(broadcast.toOctets());
            options.add(option);

            // domain server
            option = new DhcpOption();
            option.setCode(OptionCode_DomainServer.getValue());
            option.setLength((byte) 4);
            option.setData(DEFAULT_DNS.toOctets());
            options.add(option);

            // TODO fix MTU value to be configurable
            option = new DhcpOption();
            option.setCode(DHCP_OPTION_MTU);
            option.setLength((byte) 2);
            option.setData(DHCP_DATA_MTU_DEFAULT);
            options.add(option);

            // router address
            if (snet.type() != MANAGEMENT_LOCAL && snet.type() != MANAGEMENT_HOST) {
                option = new DhcpOption();
                option.setCode(OptionCode_RouterAddress.getValue());
                option.setLength((byte) 4);
                option.setData(serverIp.toOctets());
                options.add(option);
            }

            // classless static routes
            byte[] data = getClasslessStaticRoutesData(snet);
            if (data.length >= 5) {
                option = new DhcpOption();
                option.setCode(DHCP_OPTION_CLASSLESS_STATIC_ROUTE);
                option.setLength((byte) data.length);
                option.setData(data);
                options.add(option);
            }

            // end option
            option = new DhcpOption();
            option.setCode(OptionCode_END.getValue());
            option.setLength((byte) 1);
            options.add(option);

            dhcpReply.setOptions(options);
            return dhcpReply;
        }

        private byte[] getClasslessStaticRoutesData(ServiceNetwork snet) {
            List<Byte> result = Lists.newArrayList();
            List<Byte> router = Bytes.asList(snet.serviceIp().toOctets());

            // static routes for the providers
            Set<ServiceNetwork> providers = snet.providers().keySet().stream()
                    .map(provider -> snetService.serviceNetwork(provider))
                    .filter(Objects::nonNull)
                    .collect(Collectors.toSet());

            providers.forEach(provider -> {
                result.add((byte) provider.subnet().prefixLength());
                result.addAll(getSignificantOctets(provider.subnet()));
                result.addAll(router);
            });

            // static routes for the bidirectional subscribers
            Set<ServiceNetwork> subscribers = snetService.serviceNetworks().stream()
                    .filter(net -> isBidirectionalProvider(net, snet.id()))
                    .collect(Collectors.toSet());

            subscribers.forEach(subscriber -> {
                result.add((byte) subscriber.subnet().prefixLength());
                result.addAll(getSignificantOctets(subscriber.subnet()));
                result.addAll(router);
            });

            return Bytes.toArray(result);
        }

        private boolean isBidirectionalProvider(ServiceNetwork snet, NetworkId targetNetId) {
            return snet.providers().entrySet().stream()
                    .filter(p -> Objects.equals(p.getKey(), targetNetId))
                    .anyMatch(p -> p.getValue() == BIDIRECTIONAL);
        }

        private List<Byte> getSignificantOctets(IpPrefix ipPrefix) {
            int numOfOctets = ipPrefix.prefixLength() / 8;
            if (ipPrefix.prefixLength() % 8 != 0) {
                numOfOctets += 1;
            }
            byte[] result = Arrays.copyOfRange(ipPrefix.address().toOctets(), 0, numOfOctets);
            return Bytes.asList(result);
        }
    }
}