/*
    ESP8266 LLMNR responder
    Copyright (C) 2017 Stephen Warren <swarren@wwwdotorg.org>

    Based on:
    ESP8266 Multicast DNS (port of CC3000 Multicast DNS library)
    Version 1.1
    Copyright (c) 2013 Tony DiCola (tony@tonydicola.com)
    ESP8266 port (c) 2015 Ivan Grokhotkov (ivan@esp8266.com)
    MDNS-SD Suport 2015 Hristo Gochkov
    Extended MDNS-SD support 2016 Lars Englund (lars.englund@gmail.com)

    License (MIT license):

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.

    Reference:
    https://tools.ietf.org/html/rfc4795 (LLMNR)
    https://tools.ietf.org/html/rfc1035 (DNS)
*/

#include <debug.h>
#include <functional>
#include <ESP8266LLMNR.h>
#include <WiFiUdp.h>

extern "C" {
#include <user_interface.h>
}

#include <lwip/udp.h>
#include <lwip/igmp.h>
#include <include/UdpContext.h>

//#define LLMNR_DEBUG

//BIT(x) is defined in tools/sdk/c_types.h

#define FLAGS_QR                BIT(15)
#define FLAGS_OP_SHIFT          11
#define FLAGS_OP_MASK           0xf
#define FLAGS_C                 BIT(10)
#define FLAGS_TC                BIT(9)
#define FLAGS_T                 BIT(8)
#define FLAGS_RCODE_SHIFT       0
#define FLAGS_RCODE_MASK        0xf

#define _conn_read16() (((uint16_t)_conn->read() << 8) | _conn->read())
#define _conn_read8() _conn->read()
#define _conn_readS(b, l) _conn->read((b), (l));

// llmnr ipv6 is FF02:0:0:0:0:0:1:3
// lwip-v2's igmp_joingroup only supports IPv4
#define LLMNR_MULTICAST_ADDR 224, 0, 0, 252
static const int LLMNR_MULTICAST_TTL = 1;
static const int LLMNR_PORT = 5355;

LLMNRResponder::LLMNRResponder() :
    _conn(0)
{
}

LLMNRResponder::~LLMNRResponder()
{
    if (_conn)
    {
        _conn->unref();
    }
}

bool LLMNRResponder::begin(const char* hostname)
{
    // Max length for a single label in DNS
    if (strlen(hostname) > 63)
    {
        return false;
    }

    _hostname = hostname;
    _hostname.toLowerCase();

    _sta_got_ip_handler = WiFi.onStationModeGotIP([this](const WiFiEventStationModeGotIP & event)
    {
        (void) event;
        _restart();
    });

    _sta_disconnected_handler = WiFi.onStationModeDisconnected([this](const WiFiEventStationModeDisconnected & event)
    {
        (void) event;
        _restart();
    });

    return _restart();
}

void LLMNRResponder::notify_ap_change()
{
    _restart();
}

bool LLMNRResponder::_restart()
{
    if (_conn)
    {
        _conn->unref();
        _conn = 0;
    }

    IPAddress llmnr(LLMNR_MULTICAST_ADDR);

    if (igmp_joingroup(IP4_ADDR_ANY4, llmnr) != ERR_OK)
    {
        return false;
    }

    _conn = new UdpContext;
    _conn->ref();

    if (!_conn->listen(IP_ADDR_ANY, LLMNR_PORT))
    {
        return false;
    }

    _conn->setMulticastTTL(LLMNR_MULTICAST_TTL);
    _conn->onRx(std::bind(&LLMNRResponder::_process_packet, this));
    _conn->connect(llmnr, LLMNR_PORT);
    return true;
}

void LLMNRResponder::_process_packet()
{
    if (!_conn || !_conn->next())
    {
        return;
    }

#ifdef LLMNR_DEBUG
    Serial.println("LLMNR: RX'd packet");
#endif

    uint16_t id = _conn_read16();
    uint16_t flags = _conn_read16();
    uint16_t qdcount = _conn_read16();
    uint16_t ancount = _conn_read16();
    uint16_t nscount = _conn_read16();
    uint16_t arcount = _conn_read16();

#ifdef LLMNR_DEBUG
    Serial.print("LLMNR: ID=");
    Serial.println(id, HEX);
    Serial.print("LLMNR: FLAGS=");
    Serial.println(flags, HEX);
    Serial.print("LLMNR: QDCOUNT=");
    Serial.println(qdcount);
    Serial.print("LLMNR: ANCOUNT=");
    Serial.println(ancount);
    Serial.print("LLMNR: NSCOUNT=");
    Serial.println(nscount);
    Serial.print("LLMNR: ARCOUNT=");
    Serial.println(arcount);
#endif

#define BAD_FLAGS (FLAGS_QR | (FLAGS_OP_MASK << FLAGS_OP_SHIFT) | FLAGS_C)
    if (flags & BAD_FLAGS)
    {
#ifdef LLMNR_DEBUG
        Serial.println("Bad flags");
#endif
        return;
    }

    if (qdcount != 1)
    {
#ifdef LLMNR_DEBUG
        Serial.println("QDCOUNT != 1");
#endif
        return;
    }

    if (ancount || nscount || arcount)
    {
#ifdef LLMNR_DEBUG
        Serial.println("AN/NS/AR-COUNT != 0");
#endif
        return;
    }

    uint8_t namelen = _conn_read8();
#ifdef LLMNR_DEBUG
    Serial.print("QNAME len ");
    Serial.println(namelen);
#endif
    if (namelen != _hostname.length())
    {
#ifdef LLMNR_DEBUG
        Serial.println("QNAME len mismatch");
#endif
        return;
    }

    char qname[64];
    _conn_readS(qname, namelen);
    _conn_read8();
    qname[namelen] = '\0';
#ifdef LLMNR_DEBUG
    Serial.print("QNAME ");
    Serial.println(qname);
#endif

    if (strcmp(_hostname.c_str(), qname))
    {
#ifdef LLMNR_DEBUG
        Serial.println("QNAME mismatch");
#endif
        return;
    }

    uint16_t qtype = _conn_read16();
    uint16_t qclass = _conn_read16();

#ifdef LLMNR_DEBUG
    Serial.print("QTYPE ");
    Serial.print(qtype);
    Serial.print(" QCLASS ");
    Serial.println(qclass);
#endif

    bool have_rr =
        (qtype == 1) && /* A */
        (qclass == 1); /* IN */

    _conn->flush();

#ifdef LLMNR_DEBUG
    Serial.println("Match; responding");
    if (!have_rr)
    {
        Serial.println("(no matching RRs)");
    }
#endif

    IPAddress remote_ip = _conn->getRemoteAddress();

    struct ip_info ip_info;
    bool match_ap = false;
    if (wifi_get_opmode() & SOFTAP_MODE)
    {
        wifi_get_ip_info(SOFTAP_IF, &ip_info);
        IPAddress infoIp(ip_info.ip);
        IPAddress infoMask(ip_info.netmask);
        if (ip_info.ip.addr && ip_addr_netcmp((const ip_addr_t*)remote_ip, (const ip_addr_t*)infoIp, ip_2_ip4((const ip_addr_t*)infoMask)))
        {
            match_ap = true;
        }
    }
    if (!match_ap)
    {
        wifi_get_ip_info(STATION_IF, &ip_info);
    }
    uint32_t ip = ip_info.ip.addr;

    // Header
    uint8_t header[] =
    {
        (uint8_t)(id >> 8), (uint8_t)(id & 0xff), // ID
        (uint8_t)(FLAGS_QR >> 8), 0, // FLAGS
        0, 1, // QDCOUNT
        0, !!have_rr, // ANCOUNT
        0, 0, // NSCOUNT
        0, 0, // ARCOUNT
    };
    _conn->append(reinterpret_cast<const char*>(header), sizeof(header));
    // Question
    _conn->append(reinterpret_cast<const char*>(&namelen), 1);
    _conn->append(qname, namelen);
    uint8_t q[] =
    {
        0, // Name terminator
        0, 1, // TYPE (A)
        0, 1, // CLASS (IN)
    };
    _conn->append(reinterpret_cast<const char*>(q), sizeof(q));
    // Answer, if we have one
    if (have_rr)
    {
        _conn->append(reinterpret_cast<const char*>(&namelen), 1);
        _conn->append(qname, namelen);
        uint8_t rr[] =
        {
            0, // Name terminator
            0, 1, // TYPE (A)
            0, 1, // CLASS (IN)
            0, 0, 0, 30, // TTL (30 seconds)
            0, 4, // RDLENGTH
            (uint8_t)(ip & 0xff), (uint8_t)((ip >> 8) & 0xff), (uint8_t)((ip >> 16) & 0xff), (uint8_t)((ip >> 24) & 0xff) // RDATA
        };
        _conn->append(reinterpret_cast<const char*>(rr), sizeof(rr));
    }
    _conn->setMulticastInterface(remote_ip);
    _conn->send(remote_ip, _conn->getRemotePort());
}

#if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_LLMNR)
LLMNRResponder LLMNR;
#endif