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

const bit<8>  UDP_PROTOCOL = 0x11;
const bit<16> TYPE_IPV4 = 0x800;
const bit<5>  IPV4_OPTION_MRI = 31;

#define MAX_HOPS 9

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

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

header ipv4_option_t {
    bit<1> copyFlag;
    bit<2> optClass;
    bit<5> option;
    bit<8> optionLength;
}

header mri_t {
    bit<16>  count;
}

header switch_t {
    switchID_t  swid;
}

struct ingress_metadata_t {
    bit<16>  count;
}

struct parser_metadata_t {
    bit<16>  remaining;
}

struct metadata {
    ingress_metadata_t   ingress_metadata;
    parser_metadata_t   parser_metadata;
}

struct headers {
    ethernet_t   ethernet;
    ipv4_t       ipv4;
    ipv4_option_t  ipv4_option;
    mri_t        mri;
    switch_t[MAX_HOPS] swids;
}

error { IPHeaderTooShort }

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

parser ParserImpl(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);
        verify(hdr.ipv4.ihl >= 5, error.IPHeaderTooShort);
        transition select(hdr.ipv4.ihl) {
            5             : accept;
            default       : parse_ipv4_option;
        }
    }

    state parse_ipv4_option {
        packet.extract(hdr.ipv4_option);
        transition select(hdr.ipv4_option.option) {
            IPV4_OPTION_MRI: parse_mri;
            default: accept;
        }
    }

    state parse_mri {
        packet.extract(hdr.mri);
        meta.parser_metadata.remaining = hdr.mri.count;
        transition select(meta.parser_metadata.remaining) {
            0 : accept;
            default: parse_swid;
        }
    }

    state parse_swid {
        packet.extract(hdr.swids.next);
        meta.parser_metadata.remaining = meta.parser_metadata.remaining  - 1;
        transition select(meta.parser_metadata.remaining) {
            0 : accept;
            default: parse_swid;
        }
    }    
}


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

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


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

control ingress(inout headers hdr, inout metadata meta, inout standard_metadata_t standard_metadata) {
    action drop() {
        mark_to_drop();
    }
    
    action add_mri_option() {
        hdr.ipv4_option.setValid();
        hdr.ipv4_option.copyFlag     = 1;
        hdr.ipv4_option.optClass     = 2;  /* Debugging and Measurement */
        hdr.ipv4_option.option       = IPV4_OPTION_MRI;
        hdr.ipv4_option.optionLength = 4;  /* sizeof(ipv4_option) + sizeof(mri) */
        
        hdr.mri.setValid();
        hdr.mri.count = 0;
        hdr.ipv4.ihl = hdr.ipv4.ihl + 1;
    }
    
    action add_swid(switchID_t id) {    
        hdr.mri.count = hdr.mri.count + 1;
        hdr.swids.push_front(1);
        hdr.swids[0].swid = id;

        hdr.ipv4.ihl = hdr.ipv4.ihl + 1;
        hdr.ipv4_option.optionLength = hdr.ipv4_option.optionLength + 4;    
    }
    
    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 swid {
        actions        = { add_swid; NoAction; }
        default_action =  NoAction();      
    }
    
    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
            NoAction;
        }
        size = 1024;
        default_action = NoAction();
    }
    
    apply {
        if (hdr.ipv4.isValid()) {
            ipv4_lpm.apply();
            
            if (!hdr.mri.isValid()) {
                add_mri_option();
            }    
            
            swid.apply();
        }
    }
}

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

control egress(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 computeChecksum(
inout headers  hdr,
inout metadata meta)
{
    Checksum16() ipv4_checksum;
    
    apply {
        if (hdr.ipv4.isValid()) {
            hdr.ipv4.hdrChecksum = ipv4_checksum.get(
            {    
                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
            });
        }
    }
}

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

control DeparserImpl(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        packet.emit(hdr.ipv4);
        packet.emit(hdr.ipv4_option);
        packet.emit(hdr.mri);
        packet.emit(hdr.swids);                 
    }
}

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

V1Switch(
ParserImpl(),
verifyChecksum(),
ingress(),
egress(),
computeChecksum(),
DeparserImpl()
) main;