#include <stdio.h>
#include <string.h>

#include <arpa/inet.h>

#include "ipv4.h"
#include "udp4.h"

namespace udp4 {
  header * make_header(void * buf,
                       uint32_t source_port,
                       uint32_t destination_port,
                       uint32_t source_address,
                       uint32_t destination_address,
                       void const * payload,
                       int payload_length)
  {
    memset(buf, 0, (sizeof (header)));
    header * hdr = reinterpret_cast<header *>(buf);

    hdr->source_port = source_port;
    hdr->destination_port = destination_port;
    hdr->length = htons(payload_length + (sizeof (header)));

    ipv4_psuedo_header phdr;
    phdr.source_address = source_address;
    phdr.destination_address = destination_address;
    phdr.zeros = 0;
    phdr.protocol = ipv4::protocol::udp;
    phdr.udp_length = hdr->length; // already big endian

    uint32_t sum = 0;
    sum = ipv4::checksum_partial(sum, reinterpret_cast<void const *>(&phdr), (sizeof (ipv4_psuedo_header)));
    sum = ipv4::checksum_partial(sum, reinterpret_cast<void const *>(hdr), (sizeof (header)));
    sum = ipv4::checksum_partial(sum, reinterpret_cast<void const *>(payload), payload_length);

    hdr->checksum = htons(ipv4::checksum_finish(sum));

    return hdr;
  }
}