/*
 *------------------------------------------------------------------
 * Copyright (c) 2017 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *------------------------------------------------------------------
 */

#include <stdint.h>
#include <net/if.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/uio.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <netdb.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <netinet/if_ether.h>
#include <net/if_arp.h>
#include <asm/byteorder.h>
#include <byteswap.h>

#include <icmp_proto.h>

static uint16_t
cksum (void *addr, ssize_t len)
{
  char *data = (char *) addr;

  uint32_t acc = 0xffff;

  ssize_t i;
  for (i = 0; (i + 1) < len; i += 2)
    {
      uint16_t word;
      memcpy (&word, data + i, 2);
      acc += ntohs (word);
      if (acc > 0xffff)
	acc -= 0xffff;
    }

  if (len & 1)
    {
      uint16_t word = 0;
      memcpy (&word, data + len - 1, 1);
      acc += ntohs (word);
      if (acc > 0xffff)
	acc -= 0xffff;
    }
  return htons (~acc);
}

int
print_packet (void *pck)
{
  if (pck == NULL)
    {
      printf ("ICMP_PROTO: no data\n");
      return -1;
    }
  struct iphdr *ip;
  struct icmphdr *icmp;
  ip = (struct iphdr *) pck;
  icmp = (struct icmphdr *) (pck + sizeof (struct iphdr));
  printf ("received packet:\n");
  printf ("\tiphdr:\n");
  printf ("\t\tihl: %u\n\t\tversion: %u\n\t\tlen: %u\n\t\tid: %u\n",
	  ip->ihl, ip->version, __bswap_16 (ip->tot_len), ip->id);
  printf ("\t\tprotocol: %u\n", ip->protocol);

  printf ("\t\tsaddr: ");
  int i;
  for (i = 0; i < 4; i++)
    {
      printf ("%u.", ((uint8_t *) & ip->saddr)[i]);
    }
  printf ("\n");

  printf ("\t\tdaddr: ");
  for (i = 0; i < 4; i++)
    {
      printf ("%u.", ((uint8_t *) & ip->daddr)[i]);
    }
  printf ("\n");
  printf ("\ticmphdr:\n");
  printf ("\t\ttype: %s\n",
	  (icmp->type == ICMP_ECHO) ? "ICMP_ECHO" : "ICMP_ECHOREPLY");

  return 0;
}

static ssize_t
resolve_arp (void *arp)
{
  struct arphdr *resp = (struct arphdr *) arp;

  resp->ar_hrd = __bswap_16 (ARPHRD_ETHER);

  resp->ar_pro = __bswap_16 (0x0800);

  resp->ar_hln = 6;
  resp->ar_pln = 4;

  resp->ar_op = __bswap_16 (ARPOP_REPLY);

  return sizeof (struct arphdr);
}

static ssize_t
resolve_eth_arp (struct ether_arp *eth_arp, void *eth_arp_resp,
		 uint8_t ip_addr[4])
{
  struct ether_arp *resp = (struct ether_arp *) eth_arp_resp;

  resolve_arp (&resp->ea_hdr);

  memcpy (resp->arp_tha, eth_arp->arp_sha, 6);
  memcpy (resp->arp_tpa, eth_arp->arp_spa, 4);

  memcpy (resp->arp_sha,
	  (((struct ether_header *) (eth_arp_resp -
				     sizeof (struct ether_header)))->
	   ether_shost), 6);

  memcpy (resp->arp_spa, ip_addr, 4);

  return sizeof (struct ether_arp);
}

static ssize_t
resolve_eth (struct ether_header *eth, void *eth_resp)
{
  struct ether_header *resp = (struct ether_header *) eth_resp;
  memcpy (resp->ether_dhost, eth->ether_shost, 6);

  uint8_t hw_addr[6];
  int i;
  for (i = 0; i < 6; i++)
    {
      hw_addr[i] = 'a';
    }
  memcpy (resp->ether_shost, hw_addr, 6);

  resp->ether_type = eth->ether_type;

  return sizeof (struct ether_header);
}

static ssize_t
resolve_ip (struct iphdr *ip, void *ip_resp, uint8_t ip_addr[4])
{
  struct iphdr *resp = (struct iphdr *) ip_resp;
  resp->ihl = 5;
  resp->version = 4;
  resp->tos = 0;
  /*len updated later */
  resp->tot_len = 0x5400;
  resp->id = 0;
  resp->frag_off = 0;
  resp->ttl = 0x40;
  resp->protocol = 1;
  ((uint8_t *) & resp->saddr)[0] = ip_addr[0];
  ((uint8_t *) & resp->saddr)[1] = ip_addr[1];
  ((uint8_t *) & resp->saddr)[2] = ip_addr[2];
  ((uint8_t *) & resp->saddr)[3] = ip_addr[3];
  resp->daddr = ip->saddr;

  resp->check = cksum (resp, sizeof (struct iphdr));

  return sizeof (struct iphdr);
}

static ssize_t
resolve_icmp (struct icmphdr *icmp, void *icmp_resp)
{
  struct icmphdr *resp = (struct icmphdr *) icmp_resp;
  resp->type = ICMP_ECHOREPLY;
  resp->code = 0;
  resp->un.echo.id = icmp->un.echo.id;
  resp->un.echo.sequence = icmp->un.echo.sequence;

  /*resp->checksum = cksum (resp, sizeof (struct icmphdr)); */

  return sizeof (struct icmphdr);
}

int
resolve_packet (void *in_pck, ssize_t in_size,
		void *out_pck, uint32_t * out_size, uint8_t ip_addr[4])
{
  struct ether_header *eh;
  struct ether_arp *eah;
  struct iphdr *ip;
  struct icmphdr *icmp;
  *out_size = 0;

  eh = (struct ether_header *) in_pck;
  *out_size = resolve_eth (eh, out_pck);

  if (eh->ether_type == 0x0608)
    {
      eah = (struct ether_arp *) (in_pck + *out_size);
      *out_size += resolve_eth_arp (eah, out_pck + *out_size, ip_addr);

    }
  else if (eh->ether_type == 0x0008)
    {
#ifdef ICMP_DBG
      print_packet (in_pck + *out_size);
#endif
      ip = (struct iphdr *) (in_pck + *out_size);
      *out_size += resolve_ip (ip, out_pck + *out_size, ip_addr);
      if (ip->protocol == 1)
	{
	  icmp = (struct icmphdr *) (in_pck + *out_size);
	  *out_size += resolve_icmp (icmp, out_pck + *out_size);
	  ((struct icmphdr *) (out_pck + *out_size -
			       sizeof (struct icmphdr)))->checksum =
	    cksum (out_pck + *out_size - sizeof (struct icmphdr),
		   sizeof (struct icmphdr));
	  /* payload */
	  memcpy (out_pck + *out_size, in_pck + *out_size,
		  in_size - *out_size);
	  *out_size = in_size;
	}
    }
  return 0;
}