#include <cstdio>
#include <cstdlib>
#include <csignal>
#include <climits>
#include <cstring>
#include <unistd.h>
#include <vector>
#include <unordered_map>

extern "C" {
#include <netsim.h>
};

#define SYNC_PERIOD (500 * 1000ULL) // 500ns
#define ETH_LATENCY (500 * 1000ULL) // 500ns

/* MAC address type */
struct MAC {
    const volatile uint8_t *data;

    MAC(const volatile uint8_t *data)
        : data(data) {}

    bool operator==(const MAC &other) const {
        for (int i = 0; i < 6; i++) {
            if (data[i] != other.data[i]) {
                return false;
            }
        }
        return true;
    }
};
namespace std {
    template <>
    struct hash<MAC>
    {
        size_t operator()(const MAC &m) const {
            size_t res = 0;
            for (int i = 0; i < 6; i++) {
                res = (res << 4) | (res ^ m.data[i]);
            }
            return res;
        }
    };
} // namespace std

/* Global variables */
static uint64_t cur_ts = 0;
static int exiting = 0;
static const volatile uint8_t bcast[6] = {0xFF};
static const MAC bcast_addr(bcast);
static std::vector<struct netsim_interface> nsifs;
static std::unordered_map<MAC, int> mac_table;

static void sigint_handler(int dummy)
{
    exiting = 1;
}

static void forward_pkt(volatile struct cosim_eth_proto_d2n_send *tx, int port)
{
    volatile union cosim_eth_proto_n2d *msg_to;
    msg_to = netsim_n2d_alloc(&nsifs[port], cur_ts, ETH_LATENCY);
    if (msg_to != NULL) {
        volatile struct cosim_eth_proto_n2d_recv *rx;
        rx = &msg_to->recv;
        rx->len = tx->len;
        rx->port = 0;
        memcpy((void *)rx->data, (void *)tx->data, tx->len);

        // WMB();
        rx->own_type = COSIM_ETH_PROTO_N2D_MSG_RECV |
            COSIM_ETH_PROTO_N2D_OWN_DEV;
    } else {
        fprintf(stderr, "forward_pkt: dropping packet\n");
    }
}

static void switch_pkt(struct netsim_interface *nsif, int iport)
{
    volatile union cosim_eth_proto_d2n *msg_from = netsim_d2n_poll(nsif, cur_ts);
    if (msg_from == NULL) {
        return;
    }

    uint8_t type = msg_from->dummy.own_type & COSIM_ETH_PROTO_D2N_MSG_MASK;
    if (type == COSIM_ETH_PROTO_D2N_MSG_SEND) {
        volatile struct cosim_eth_proto_d2n_send *tx;
        tx = &msg_from->send;
        // Get MAC addresses
        MAC dst(tx->data), src(tx->data+6);
        // MAC learning
        if (!(src == bcast_addr)) {
            mac_table[src] = iport;
        }
        // L2 forwarding
        if (mac_table.count(dst) > 0) {
            int eport = mac_table.at(dst);
            forward_pkt(tx, eport);
        } else {
            // Broadcast
            for (int eport = 0; eport < nsifs.size(); eport++) {
                if (eport != iport) {
                    // Do not forward to ingress port
                    forward_pkt(tx, eport);
                }
            }
        }
    } else if (type == COSIM_ETH_PROTO_D2N_MSG_SYNC) {
    } else {
        fprintf(stderr, "switch_pkt: unsupported type=%u\n", type);
        abort();
    }
    netsim_d2n_done(nsif, msg_from);
}

int main(int argc, char *argv[])
{
    int c;

    // Parse command line argument
    while ((c = getopt(argc, argv, "s:")) != -1) {
        switch (c) {
        case 's': {
            struct netsim_interface nsif;
            int sync = 1;
            if (netsim_init(&nsif, optarg, &sync) != 0) {
                return EXIT_FAILURE;
            }
            nsifs.push_back(nsif);
        }
        default:
            fprintf(stderr, "unknown option %c\n", c);
        }
    }

    if (nsifs.empty()) {
        fprintf(stderr, "Usage: net_switch -s SOCKET-A [-s SOCKET-B ...]\n");
        return EXIT_FAILURE;
    }

    signal(SIGINT, sigint_handler);
    signal(SIGTERM, sigint_handler);

    printf("start polling\n");
    while (!exiting) {
        // Sync all interfaces
        for (auto &nsif : nsifs) {
            if (netsim_n2d_sync(&nsif, cur_ts, ETH_LATENCY, SYNC_PERIOD) != 0) {
                fprintf(stderr, "netsim_n2d_sync failed\n");
                abort();
            }
        }
        // Switch packets
        uint64_t min_ts;
        do {
            min_ts = ULLONG_MAX;
            for (int port = 0; port < nsifs.size(); port++) {
                auto &nsif = nsifs.at(port);
                switch_pkt(&nsif, port);
                if (nsif.sync) {
                    uint64_t ts = netsim_d2n_timestamp(&nsif);
                    min_ts = ts < min_ts ? ts : min_ts;
                }
            }
        } while (!exiting && (min_ts <= cur_ts));

        // Update cur_ts
        if (min_ts < ULLONG_MAX) {
            cur_ts = min_ts;
        }
    }

    return 0;
}
