#include "util.h"

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <errno.h>
#include <sys/socket.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <sys/ioctl.h>

#include <arpa/inet.h>
#include <netinet/ip.h>

void* xmalloc( size_t bytes )
{
    void* result = malloc( bytes );
    
    if ( bytes > 0 && result == NULL ) {
        warn( "Couldn't allocate memory, exiting!" );
        exit(2);
        
    }
    
    memset( result, 0, bytes );
    return result;
}

int create_tun( const char* name )
{
    int fd, err;
    struct ifreq ifr;

   if ( ( fd = open( "/dev/net/tun", O_RDWR ) ) < 0 ) {
        warn( "Error %s opening tun to create %s", strerror(errno), name );
        return -1;
    }
    
    memset( &ifr, 0, sizeof( struct ifreq ) );
    
    ifr.ifr_flags = IFF_TUN | IFF_NO_PI | IFF_UP;
    strncpy( ifr.ifr_name, name, IFNAMSIZ );
    
    if ( (err = ioctl( fd, TUNSETIFF, (void*) &ifr ) ) < 0 ) {
        warn( "Error creating tun device %s: %s", name, strerror(errno) );
        close( fd );
        return -1;
    }
    
    return fd;
}


// shamelessly copied from:
// http://www.roman10.net/how-to-calculate-iptcpudp-checksumpart-2-implementation/
unsigned short compute_checksum(unsigned short *addr, unsigned int count) {

  unsigned long sum = 0;

  while (count > 1) {
    sum += * addr++;
    count -= 2;
  }

  //if any bytes left, pad the bytes and add
  if(count > 0) {
    sum += ((*addr)&htons(0xFF00));
  }

  //Fold sum to 16 bits: add carrier to result
  while (sum>>16) {
      sum = (sum & 0xffff) + (sum >> 16);
  }

  //one's complement
  sum = ~sum;

  return ((unsigned short)sum);

}

void compute_ip_checksum(struct iphdr* pkt)
{
  pkt->check = 0x0000;
  pkt->check = compute_checksum( (unsigned short*) pkt, pkt->ihl * 4 );
}



int link_set_up( char *link_name, int state )
{
    int fd = socket( PF_INET, SOCK_DGRAM, IPPROTO_IP );
    struct ifreq ifr;


    memset( &ifr, 0, sizeof( struct ifreq ) );
    strncpy( ifr.ifr_name, link_name, IFNAMSIZ );
    
    if ( ioctl( fd, SIOCGIFFLAGS, (void*)&ifr ) < 0 ) {
        warn( "Failed to read interface flags for %s: %s", link_name, strerror(errno) );
        return 0;
    }
    
    if ( state ) {
        ifr.ifr_flags |= IFF_UP;
    } else {
        ifr.ifr_flags = ( ifr.ifr_flags & ~IFF_UP );
    }
    
    if ( ioctl( fd, SIOCSIFFLAGS, (void*)&ifr ) < 0 ) {
        warn( "Failed to set link state for interface %s to %i: %s", link_name, state, strerror(errno) );
        return 0;
    }

    return 1;

}