#pragma once

#include <stdint.h>

namespace ip4 {

  struct header {
    uint8_t version_ihl;
    uint8_t type_of_service;
    uint16_t total_length;
    uint16_t identification;
    uint16_t fragment_offset;
    uint8_t time_to_live;
    uint8_t protocol;
    uint16_t header_checksum;
    uint32_t source_address;
    uint32_t destination_address;
  };

  static_assert((sizeof (header)) == 20);

  char const * tostr(uint32_t a);

  uint32_t checksum_partial(uint32_t sum, void const * src, int length);
  uint32_t checksum_finish(uint32_t sum);
  uint32_t checksum(void const * src, int length);

  header * make_header(void * buf,
                       uint16_t payload_length,
                       uint16_t identification,
                       uint32_t source_address, // big endian
                       uint32_t destination_address); // big endian

  struct protocol {
    enum {
      udp = 17,
    };
  };
}