/* vim: set expandtab ts=4 sw=4: */
/*
 * You may redistribute this program and/or modify it under the terms of
 * the GNU General Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
#include "interface/tuntap/TAPWrapper.h"
#include "interface/tuntap/TUNMessageType.h"
#include "util/Bits.h"
#include "util/Identity.h"
#include "util/AddrTools.h"
#include "util/Defined.h"
#include "wire/Message.h"
#include "wire/Ethernet.h"
#include "wire/Error.h"

struct TAPWrapper_pvt
{
    struct TAPWrapper pub;
    struct Iface external;
    struct Log* log;
    Identity
};

static Iface_DEFUN receiveMessage(struct Message* msg, struct Iface* external)
{
    struct TAPWrapper_pvt* tw = Identity_containerOf(external, struct TAPWrapper_pvt, external);

    if (Message_getLength(msg) < Ethernet_SIZE-2) {
        Log_debug(tw->log, "runt");
        return Error(msg, "RUNT");
    }

    // wacky 14 byte headers, back off into outer-space to create the padding...
    Er_assert(Message_eshift(msg, 2));

    struct Ethernet eth;
    Er_assert(Message_epop(msg, &eth, sizeof(struct Ethernet)));

    // Not for us and not multicast...
    if (Bits_memcmp(eth.destAddr, TAPWrapper_LOCAL_MAC, Ethernet_ADDRLEN)
        && !(eth.destAddr[0] & 0x01))
    {
        if (Defined(Log_DEBUG)) {
            uint8_t printedMac[18];
            AddrTools_printMac(printedMac, eth.destAddr);
            Log_debug(tw->log, "Packet destine for unknown ethernet MAC [%s]", printedMac);
        }
        //return 0;
    }

    if (Bits_memcmp(eth.srcAddr, tw->pub.peerAddress, Ethernet_ADDRLEN)) {
        if (Bits_isZero(tw->pub.peerAddress, Ethernet_ADDRLEN)) {
            Bits_memcpy(tw->pub.peerAddress, eth.srcAddr, Ethernet_ADDRLEN);
        } else {
            #ifdef Log_DEBUG
                uint8_t printedMac[18];
                AddrTools_printMac(printedMac, eth.srcAddr);
                Log_debug(tw->log, "DROP Packet with unexpected source MAC [%s]", printedMac);
            #endif
            return Error(msg, "INVALID");
        }
    }
    Er_assert(TUNMessageType_push(msg, eth.ethertype));
    return Iface_next(&tw->pub.internal, msg);
}

static Iface_DEFUN sendMessage(struct Message* msg, struct Iface* internal)
{
    struct TAPWrapper_pvt* tw = Identity_containerOf(internal, struct TAPWrapper_pvt, pub.internal);

    uint16_t etherType = Er_assert(TUNMessageType_pop(msg));
    struct Ethernet eth = { .ethertype = etherType };
    Bits_memcpy(eth.srcAddr, TAPWrapper_LOCAL_MAC, Ethernet_ADDRLEN);
    Bits_memcpy(eth.destAddr, tw->pub.peerAddress, Ethernet_ADDRLEN);
    if (Bits_isZero(tw->pub.peerAddress, Ethernet_ADDRLEN)) {
        Log_debug(tw->log, "DROP Packet because peers MAC is not yet known");
        return Error(msg, "INVALID");
    }

    Er_assert(Message_epush(msg, &eth, sizeof(struct Ethernet)));

    // struct Ethernet contains 2 bytes of padding at the beginning.
    Er_assert(Message_eshift(msg, -2));

    return Iface_next(&tw->external, msg);
}

struct TAPWrapper* TAPWrapper_new(struct Iface* external,
                                  struct Log* log,
                                  struct Allocator* alloc)
{
    struct TAPWrapper_pvt* out = Allocator_calloc(alloc, sizeof(struct TAPWrapper_pvt), 1);
    Identity_set(out);
    out->log = log;
    out->external.send = receiveMessage;
    out->pub.internal.send = sendMessage;
    Iface_plumb(external, &out->external);
    return &out->pub;
}