/*
 * Since the rust ioctl bindings don't have all the structures and constants,
 * it's easier to just write the thing in C and link it in.
 */

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

#include <sys/socket.h>
#ifdef __linux__
#include <linux/if.h>
#include <linux/if_tun.h>
#else
#include <net/if.h>
#define IFF_TUN 0x0001
#define IFF_TAP 0x0002
#define IFF_NO_PI 0x1000
#define TUNSETIFF _IOW('T', 202, int)
#endif
#include <sys/ioctl.h>

/**
 * fd ‒ the fd to turn into TUN or TAP.
 * name ‒ the name to use. If empty, kernel will assign something by itself.
 *   Must be buffer with capacity at least 33.
 * mode ‒ 1 = TUN, 2 = TAP.
 * packet_info ‒ if packet info should be provided, if the given value is 0 it will not prepend packet info.
 */
int tuntap_setup(int fd, unsigned char *name, int mode, int packet_info)
{
    struct ifreq ifr;
    memset(&ifr, 0, sizeof ifr);
    switch (mode)
    {
    case 1:
        ifr.ifr_flags = IFF_TUN;
        break;
    case 2:
        ifr.ifr_flags = IFF_TAP;
        break;
    default:
        assert(0);
    }

    // If no packet info needs to be provided add corresponding flag
    if (!packet_info)
    {
        ifr.ifr_flags |= IFF_NO_PI;
    }

    // Leave one for terminating '\0'. No idea if it is needed, didn't find
    // it in the docs, but assuming the worst.
    strncpy(ifr.ifr_name, (char *)name, IFNAMSIZ - 1);

    int ioresult = ioctl(fd, TUNSETIFF, &ifr);
    if (ioresult < 0)
    {
        return ioresult;
    }
    strncpy((char *)name, ifr.ifr_name, IFNAMSIZ < 32 ? IFNAMSIZ : 32);
    name[32] = '\0';
    return 0;
}