#include <tins/tins.h>
#include <map>
#include <iostream>
#include <functional>

using namespace Tins;

class arp_monitor {
public:
    void run(Sniffer &sniffer);
private:
    bool callback(const PDU &pdu);

    std::map<IPv4Address, HWAddress<6>> addresses;
};

void arp_monitor::run(Sniffer &sniffer)
{
    sniffer.sniff_loop(
        std::bind(
            &arp_monitor::callback,
            this,
            std::placeholders::_1
        )
    );
}

bool arp_monitor::callback(const PDU &pdu)
{
    // Retrieve the ARP layer
    const ARP &arp = pdu.rfind_pdu<ARP>();
    // Is it an ARP reply?
    if(arp.opcode() == ARP::REPLY) {
        // Let's check if there's already an entry for this address
        auto iter = addresses.find(arp.sender_ip_addr());
        if(iter == addresses.end()) {
            // We haven't seen this address. Save it.
            addresses.insert({ arp.sender_ip_addr(), arp.sender_hw_addr()});
            std::cout << "[INFO] " << arp.sender_ip_addr() << " is at "
                      << arp.sender_hw_addr() << std::endl;
        }
        else {
            // We've seen this address. If it's not the same HW address, inform it
            if(arp.sender_hw_addr() != iter->second) {
                std::cout << "[WARNING] " << arp.sender_ip_addr() << " is at " 
                          << iter->second << " but also at " << arp.sender_hw_addr() 
                          << std::endl;
            }
        }
    }
    return true;
}

int main(int argc, char *argv[]) 
{
    if(argc != 2) {
        std::cout << "Usage: " << *argv << " <interface>\n";
        return 1;
    }
    arp_monitor monitor;
    Sniffer sniffer(argv[1], 2000, true, "arp");
    monitor.run(sniffer);
}