/* -*- P4_16 -*- */
#include <core.p4>
#include <v1model.p4>

const bit<16> TYPE_IPV4 = 0x800;
const bit<8> protocolIPv4 = 0x04;

/*************************************************************************
*********************** H E A D E R S  ***********************************
*************************************************************************/

typedef bit<9>  egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

header ethernet_t {
    macAddr_t dstAddr;
    macAddr_t srcAddr;
    bit<16>   etherType;
}

header ipv4_t {
    bit<4>    version;
    bit<4>    ihl;
    bit<8>    diffserv;
    bit<16>   totalLen;
    bit<16>   identification;
    bit<3>    flags;
    bit<13>   fragOffset;
    bit<8>    ttl;
    bit<8>    protocol;
    bit<16>   hdrChecksum;
    ip4Addr_t srcAddr;
    ip4Addr_t dstAddr;
}

struct metadata {
    /* empty */
}

struct headers {
    ethernet_t   ethernet;
    ipv4_t       tunnelheader;
    ipv4_t       ipv4;
}

/*************************************************************************
*********************** P A R S E R  ***********************************
*************************************************************************/

parser MyParser(packet_in packet,
                out headers hdr,
                inout metadata meta,
                inout standard_metadata_t standard_metadata) {

    state start {
        transition parse_ethernet;
    }

    state parse_ethernet {
        packet.extract(hdr.ethernet);
        transition select(hdr.ethernet.etherType) {
            TYPE_IPV4: parse_ipv4;
            default: accept;
        }
    }

    state parse_ipv4 {
        packet.extract(hdr.ipv4);
        transition accept;
    }
}

/*************************************************************************
************   C H E C K S U M    V E R I F I C A T I O N   *************
*************************************************************************/

control MyVerifyChecksum(inout headers hdr, inout metadata meta) {
    apply {  }
}


/*************************************************************************
**************  I N G R E S S   P R O C E S S I N G   *******************
*************************************************************************/



control MyIngress(inout headers hdr,
                  inout metadata meta,
                  inout standard_metadata_t standard_metadata) {

    // define Registers for sequence number:
    register<bit<16>>(8192) nextInSequenceNumber;
    register<bit<16>>(8192) nextOutSequenceNumber;

    // let a packet enter a tunnel
    action protectionPush() {
        bit<16> tempSeqNum;
        const ip4Addr_t addrh1 = 0x0A000101;
        const ip4Addr_t addrs1 = 0x0A010001;
        const ip4Addr_t addrs3 = 0x0A030003;

        nextOutSequenceNumber.read(tempSeqNum, 0);
        // add header
        if (hdr.ipv4.srcAddr == addrh1) {
            hdr.tunnelheader.srcAddr = addrs1;
            hdr.tunnelheader.dstAddr = addrs3;
        } else {
            hdr.tunnelheader.srcAddr = addrs3;
            hdr.tunnelheader.dstAddr = addrs1;
        }
        hdr.tunnelheader.version = 0x4;
        hdr.tunnelheader.ihl = 0x5;
        hdr.tunnelheader.diffserv = 0x00;
        hdr.tunnelheader.totalLen = (hdr.ipv4.totalLen + 20);
        hdr.tunnelheader.identification = tempSeqNum;
        hdr.tunnelheader.flags = 0b000;
        hdr.tunnelheader.fragOffset = 0b0000000000000;
        hdr.tunnelheader.ttl = 0xFF;
        hdr.tunnelheader.protocol = protocolIPv4;
        tempSeqNum = tempSeqNum + 1;
        nextOutSequenceNumber.write(0, tempSeqNum);
        update_checksum(
    	    hdr.tunnelheader.isValid(),
                { hdr.tunnelheader.version,
    	          hdr.tunnelheader.ihl,
                  hdr.tunnelheader.diffserv,
                  hdr.tunnelheader.totalLen,
                  hdr.tunnelheader.identification,
                  hdr.tunnelheader.flags,
                  hdr.tunnelheader.fragOffset,
                  hdr.tunnelheader.ttl,
                  hdr.tunnelheader.protocol,
                  hdr.tunnelheader.srcAddr,
                  hdr.tunnelheader.dstAddr },
                hdr.tunnelheader.hdrChecksum,
                HashAlgorithm.csum16);
        // clone packet
        standard_metadata.egress_spec = 2;
        clone(CloneType.I2E, 3);
    }

    // Let the tunneled packet leave the tunnel
    action protectionPop() {
        bit<16> tempSeqNum;
        nextInSequenceNumber.read(tempSeqNum, 0);
        if (hdr.ipv4.identification == tempSeqNum) {
            // remove header and forward
            hdr.ipv4.setInvalid();
            // increase Sequence Number
            tempSeqNum = tempSeqNum + 1;
            nextInSequenceNumber.write(0, tempSeqNum);
        } else {
            mark_to_drop();
        }
    }

    action drop() {
        mark_to_drop();
    }

    action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
        standard_metadata.egress_spec = port;
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = dstAddr;
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
    }

    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
            NoAction;
        }
        size = 1024;
        default_action = drop();
    }


    apply {
        if (hdr.ipv4.isValid()) {
            if (standard_metadata.ingress_port == 1) {
                protectionPush();
            } else {
                protectionPop();
            }
       		ipv4_lpm.apply();
        }
    }
}

/*************************************************************************
****************  E G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyEgress(inout headers hdr,
                 inout metadata meta,
                 inout standard_metadata_t standard_metadata) {


    apply {  }
}

/*************************************************************************
*************   C H E C K S U M    C O M P U T A T I O N   **************
*************************************************************************/

control MyComputeChecksum(inout headers  hdr, inout metadata meta) {
     apply {
	update_checksum(
	    hdr.ipv4.isValid(),
            { hdr.ipv4.version,
	      hdr.ipv4.ihl,
              hdr.ipv4.diffserv,
              hdr.ipv4.totalLen,
              hdr.ipv4.identification,
              hdr.ipv4.flags,
              hdr.ipv4.fragOffset,
              hdr.ipv4.ttl,
              hdr.ipv4.protocol,
              hdr.ipv4.srcAddr,
              hdr.ipv4.dstAddr },
            hdr.ipv4.hdrChecksum,
            HashAlgorithm.csum16);
    }
}

/*************************************************************************
***********************  D E P A R S E R  *******************************
*************************************************************************/

control MyDeparser(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        packet.emit(hdr.tunnelheader);
        packet.emit(hdr.ipv4);
    }
}

/*************************************************************************
***********************  S W I T C H  *******************************
*************************************************************************/

V1Switch(
MyParser(),
MyVerifyChecksum(),
MyIngress(),
MyEgress(),
MyComputeChecksum(),
MyDeparser()
) main;