#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#include <linux/if.h>
#include <linux/if_tun.h>

#include <pthread.h>

#include "spi.h"
#include "tun.h"

static pthread_t read_thd;

static int tun_fd;
static char tun_name[IFNAMSIZ];

static int tun_alloc(char *dev, int flags) {
    struct ifreq ifr;
    int fd, err;
    char *clonedev = "/dev/net/tun";

    /* Arguments taken by the function:
     *
     * char *dev: the name of an interface (or '\0'). MUST have enough
     *   space to hold the interface name if '\0' is passed
     * int flags: interface flags (eg, IFF_TUN etc.)
     */

    fd = open(clonedev, O_RDWR);
    if (fd < 0) {
        return fd;
    }

    memset(&ifr, 0, sizeof(ifr));
    ifr.ifr_flags = flags;  /* IFF_TUN or IFF_TAP, plus maybe IFF_NO_PI */

    if (*dev) {
        /* if a device name was specified, put it in the structure; otherwise,
         * the kernel will try to allocate the "next" device of the
         * specified type */
        strncpy(ifr.ifr_name, dev, IFNAMSIZ);
    }

    /* try to create the device */
    err = ioctl(fd, TUNSETIFF, (void *) &ifr);
    if (err < 0) {
        close(fd);
        return err;
    }

    /* if the operation was successful, write back the name of the
     * interface to the variable "dev", so the caller can know
     * it. Note that the caller MUST reserve space in *dev (see calling
     * code below) */
    strcpy(dev, ifr.ifr_name);

    /* this is the special file descriptor that the caller will use to talk
     * with the virtual interface */
    return fd;
}

ssize_t tun_read(unsigned char *buffer, size_t buf_size) {
    return read(tun_fd, buffer, buf_size);
}

ssize_t tun_write(unsigned char *buffer, size_t buf_len) {
    return write(tun_fd, buffer, buf_len);
}

int tun_init(char *name) {
    int rv;

    if (strlen(name) >= sizeof(tun_name) - 1) return -1;
    strcpy(tun_name, name);

    tun_fd = tun_alloc(tun_name, IFF_TUN | IFF_NO_PI);
    if (tun_fd < 0) return -1;

    return 0;
}