#include <assert.h>
#include <stdint.h>
#include <stddef.h>
#include <string.h>

#include <arpa/inet.h>

#include "ip4.h"

namespace ip4 {

  char const * tostr(uint32_t a)
  {
    static char tmp[16];
    return inet_ntop(AF_INET, reinterpret_cast<void const *>(&a), tmp, 16);
  }

  uint32_t fromstr(char const * s)
  {
    uint32_t value;
    int ret = inet_pton(AF_INET, s, reinterpret_cast<void *>(&value));
    assert(ret == 1);
    return value;
  }

  uint32_t checksum_partial(uint32_t sum, void const * src, int length)
  {
    uint8_t const * addr = reinterpret_cast<uint8_t const *>(src);

    ptrdiff_t i = 0;
    while (length >= 2) {
      sum += (addr[i+0] << 8) | (addr[i+1] << 0);
      i += 2;
      length -= 2;
    }

    if (length > 0) {
      sum += (addr[i+0] << 8);
    }

    return sum;
  }

  uint32_t checksum_finish(uint32_t sum)
  {
    while (sum >> 16) {
      sum = (sum & 0xffff) + (sum >> 16);
    }

    return static_cast<uint16_t>(~sum);
  }

  uint32_t checksum(void const * src, int length)
  {
    uint32_t sum = checksum_partial(0, src, length);
    return checksum_finish(sum);
  }

  header * make_header(void * buf,
                       uint16_t payload_length,
                       uint16_t identification,
                       uint32_t source_address, // big endian
                       uint32_t destination_address) // big endian
  {
    memset(buf, 0, (sizeof (header)));
    header * hdr = reinterpret_cast<header *>(buf);

    const int version = 4;
    const int ihl = (sizeof (header)) / 4;
    const int total_length = payload_length + (sizeof (header));

    hdr->version_ihl = (version << 4) | (ihl << 0);
    //hdr->type_of_service = 0xb8;
    hdr->total_length = htons(total_length);
    hdr->identification = htons(identification);
    hdr->time_to_live = 64;
    hdr->protocol = protocol::udp;
    hdr->source_address = source_address;
    hdr->destination_address = destination_address;

    hdr->header_checksum = htons(checksum(buf, (sizeof (header))));

    return hdr;
  }
}