/*
 *  V4L2 video capture example
 *
 *  This program can be used and distributed without restrictions.
 *
 *      This program is provided with the V4L2 API
 * see https://linuxtv.org/docs.php for more information
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <linux/videodev2.h>

#define CLEAR(x) memset(&(x), 0, sizeof(x))

enum io_method {
    IO_METHOD_READ,
    IO_METHOD_MMAP,
    IO_METHOD_USERPTR,
};

struct buffer {
    void   *start;
    size_t  length;
};

static char            *dev_name;
static enum io_method   io = IO_METHOD_MMAP;
static int              fd = -1;
struct buffer          *buffers;
static unsigned int     n_buffers;
static int              out_buf;
static int              force_format;
static int              frame_count = 70;

static void errno_exit(const char *s)
{
    fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
    exit(EXIT_FAILURE);
}

static int xioctl(int fh, int request, void *arg)
{
    int r;

    do {
	    r = ioctl(fh, request, arg);
    } while (-1 == r && EINTR == errno);

    return r;
}

static void process_image(const void *p, int size)
{
    if (out_buf)
	    fwrite(p, size, 1, stdout);

    fflush(stderr);
    fprintf(stderr, ".");
    fflush(stdout);
}

static int read_frame(void)
{
    struct v4l2_buffer buf;
    unsigned int i;

    switch (io) {
    case IO_METHOD_READ:
	    if (-1 == read(fd, buffers[0].start, buffers[0].length)) {
		    switch (errno) {
		    case EAGAIN:
			    return 0;

		    case EIO:
			    /* Could ignore EIO, see spec. */

			    /* fall through */

		    default:
			    errno_exit("read");
		    }
	    }

	    process_image(buffers[0].start, buffers[0].length);
	    break;

    case IO_METHOD_MMAP:
	    CLEAR(buf);

	    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    buf.memory = V4L2_MEMORY_MMAP;

	    if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
		    switch (errno) {
		    case EAGAIN:
			    return 0;

		    case EIO:
			    /* Could ignore EIO, see spec. */

			    /* fall through */

		    default:
			    errno_exit("VIDIOC_DQBUF");
		    }
	    }

	    assert(buf.index < n_buffers);

	    process_image(buffers[buf.index].start, buf.bytesused);

	    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
		    errno_exit("VIDIOC_QBUF");
	    break;

    case IO_METHOD_USERPTR:
	    CLEAR(buf);

	    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    buf.memory = V4L2_MEMORY_USERPTR;

	    if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
		    switch (errno) {
		    case EAGAIN:
			    return 0;

		    case EIO:
			    /* Could ignore EIO, see spec. */

			    /* fall through */

		    default:
			    errno_exit("VIDIOC_DQBUF");
		    }
	    }

	    for (i = 0; i < n_buffers; ++i)
		    if (buf.m.userptr == (unsigned long)buffers[i].start
			&& buf.length == buffers[i].length)
			    break;

	    assert(i < n_buffers);

	    process_image((void *)buf.m.userptr, buf.bytesused);

	    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
		    errno_exit("VIDIOC_QBUF");
	    break;
    }

    return 1;
}

static void mainloop(void)
{
    unsigned int count;

    count = frame_count;

    while (count-- > 0) {
	    for (;;) {
		    fd_set fds;
		    struct timeval tv;
		    int r;

		    FD_ZERO(&fds);
		    FD_SET(fd, &fds);

		    /* Timeout. */
		    tv.tv_sec = 2;
		    tv.tv_usec = 0;

		    r = select(fd + 1, &fds, NULL, NULL, &tv);

		    if (-1 == r) {
			    if (EINTR == errno)
				    continue;
			    errno_exit("select");
		    }

		    if (0 == r) {
			    fprintf(stderr, "select timeout\n");
			    exit(EXIT_FAILURE);
		    }

		    if (read_frame())
			    break;
		    /* EAGAIN - continue select loop. */
	    }
    }
}

static void stop_capturing(void)
{
    enum v4l2_buf_type type;

    switch (io) {
    case IO_METHOD_READ:
	    /* Nothing to do. */
	    break;

    case IO_METHOD_MMAP:
    case IO_METHOD_USERPTR:
	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
		    errno_exit("VIDIOC_STREAMOFF");
	    break;
    }
}

static void start_capturing(void)
{
    unsigned int i;
    enum v4l2_buf_type type;

    switch (io) {
    case IO_METHOD_READ:
	    /* Nothing to do. */
	    break;

    case IO_METHOD_MMAP:
	    for (i = 0; i < n_buffers; ++i) {
		    struct v4l2_buffer buf;

		    CLEAR(buf);
		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		    buf.memory = V4L2_MEMORY_MMAP;
		    buf.index = i;

		    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
			    errno_exit("VIDIOC_QBUF");
	    }
	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
		    errno_exit("VIDIOC_STREAMON");
	    break;

    case IO_METHOD_USERPTR:
	    for (i = 0; i < n_buffers; ++i) {
		    struct v4l2_buffer buf;

		    CLEAR(buf);
		    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		    buf.memory = V4L2_MEMORY_USERPTR;
		    buf.index = i;
		    buf.m.userptr = (unsigned long)buffers[i].start;
		    buf.length = buffers[i].length;

		    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
			    errno_exit("VIDIOC_QBUF");
	    }
	    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
		    errno_exit("VIDIOC_STREAMON");
	    break;
    }
}

static void uninit_device(void)
{
    unsigned int i;

    switch (io) {
    case IO_METHOD_READ:
	    free(buffers[0].start);
	    break;

    case IO_METHOD_MMAP:
	    for (i = 0; i < n_buffers; ++i)
		    if (-1 == munmap(buffers[i].start, buffers[i].length))
			    errno_exit("munmap");
	    break;

    case IO_METHOD_USERPTR:
	    for (i = 0; i < n_buffers; ++i)
		    free(buffers[i].start);
	    break;
    }

    free(buffers);
}

static void init_read(unsigned int buffer_size)
{
    buffers = calloc(1, sizeof(*buffers));

    if (!buffers) {
	    fprintf(stderr, "Out of memory\n");
	    exit(EXIT_FAILURE);
    }

    buffers[0].length = buffer_size;
    buffers[0].start = malloc(buffer_size);

    if (!buffers[0].start) {
	    fprintf(stderr, "Out of memory\n");
	    exit(EXIT_FAILURE);
    }
}

static void init_mmap(void)
{
    struct v4l2_requestbuffers req;

    CLEAR(req);

    req.count = 4;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
	    if (EINVAL == errno) {
		    fprintf(stderr, "%s does not support "
			     "memory mapping\n", dev_name);
		    exit(EXIT_FAILURE);
	    } else {
		    errno_exit("VIDIOC_REQBUFS");
	    }
    }

    if (req.count < 2) {
	    fprintf(stderr, "Insufficient buffer memory on %s\n",
		     dev_name);
	    exit(EXIT_FAILURE);
    }

    buffers = calloc(req.count, sizeof(*buffers));

    if (!buffers) {
	    fprintf(stderr, "Out of memory\n");
	    exit(EXIT_FAILURE);
    }

    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
	    struct v4l2_buffer buf;

	    CLEAR(buf);

	    buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    buf.memory      = V4L2_MEMORY_MMAP;
	    buf.index       = n_buffers;

	    if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
		    errno_exit("VIDIOC_QUERYBUF");

	    buffers[n_buffers].length = buf.length;
	    buffers[n_buffers].start =
		    mmap(NULL /* start anywhere */,
			  buf.length,
			  PROT_READ | PROT_WRITE /* required */,
			  MAP_SHARED /* recommended */,
			  fd, buf.m.offset);

	    if (MAP_FAILED == buffers[n_buffers].start)
		    errno_exit("mmap");
    }
}

static void init_userp(unsigned int buffer_size)
{
    struct v4l2_requestbuffers req;

    CLEAR(req);

    req.count  = 4;
    req.type   = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_USERPTR;

    if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
	    if (EINVAL == errno) {
		    fprintf(stderr, "%s does not support "
			     "user pointer i/o\n", dev_name);
		    exit(EXIT_FAILURE);
	    } else {
		    errno_exit("VIDIOC_REQBUFS");
	    }
    }

    buffers = calloc(4, sizeof(*buffers));

    if (!buffers) {
	    fprintf(stderr, "Out of memory\n");
	    exit(EXIT_FAILURE);
    }

    for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
	    buffers[n_buffers].length = buffer_size;
	    buffers[n_buffers].start = malloc(buffer_size);

	    if (!buffers[n_buffers].start) {
		    fprintf(stderr, "Out of memory\n");
		    exit(EXIT_FAILURE);
	    }
    }
}

static void init_device(void)
{
    struct v4l2_capability cap;
    struct v4l2_cropcap cropcap;
    struct v4l2_crop crop;
    struct v4l2_format fmt;
    unsigned int min;

    if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
	    if (EINVAL == errno) {
		    fprintf(stderr, "%s is no V4L2 device\n",
			     dev_name);
		    exit(EXIT_FAILURE);
	    } else {
		    errno_exit("VIDIOC_QUERYCAP");
	    }
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
	    fprintf(stderr, "%s is no video capture device\n",
		     dev_name);
	    exit(EXIT_FAILURE);
    }

    switch (io) {
    case IO_METHOD_READ:
	    if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
		    fprintf(stderr, "%s does not support read i/o\n",
			     dev_name);
		    exit(EXIT_FAILURE);
	    }
	    break;

    case IO_METHOD_MMAP:
    case IO_METHOD_USERPTR:
	    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
		    fprintf(stderr, "%s does not support streaming i/o\n",
			     dev_name);
		    exit(EXIT_FAILURE);
	    }
	    break;
    }


    /* Select video input, video standard and tune here. */


    CLEAR(cropcap);

    cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
	    crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	    crop.c = cropcap.defrect; /* reset to default */

	    if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) {
		    switch (errno) {
		    case EINVAL:
			    /* Cropping not supported. */
			    break;
		    default:
			    /* Errors ignored. */
			    break;
		    }
	    }
    } else {
	    /* Errors ignored. */
    }


    CLEAR(fmt);

    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (force_format) {
	    fmt.fmt.pix.width       = 640;
	    fmt.fmt.pix.height      = 480;
	    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
	    fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;

	    if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
		    errno_exit("VIDIOC_S_FMT");

	    /* Note VIDIOC_S_FMT may change width and height. */
    } else {
	    /* Preserve original settings as set by v4l2-ctl for example */
	    if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt))
		    errno_exit("VIDIOC_G_FMT");
    }

    /* Buggy driver paranoia. */
    min = fmt.fmt.pix.width * 2;
    if (fmt.fmt.pix.bytesperline < min)
	    fmt.fmt.pix.bytesperline = min;
    min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
    if (fmt.fmt.pix.sizeimage < min)
	    fmt.fmt.pix.sizeimage = min;

    switch (io) {
    case IO_METHOD_READ:
	    init_read(fmt.fmt.pix.sizeimage);
	    break;

    case IO_METHOD_MMAP:
	    init_mmap();
	    break;

    case IO_METHOD_USERPTR:
	    init_userp(fmt.fmt.pix.sizeimage);
	    break;
    }
}

static void close_device(void)
{
    if (-1 == close(fd))
	    errno_exit("close");

    fd = -1;
}

static void open_device(void)
{
    struct stat st;

    if (-1 == stat(dev_name, &st)) {
	    fprintf(stderr, "Cannot identify '%s': %d, %s\n",
		     dev_name, errno, strerror(errno));
	    exit(EXIT_FAILURE);
    }

    if (!S_ISCHR(st.st_mode)) {
	    fprintf(stderr, "%s is no device\n", dev_name);
	    exit(EXIT_FAILURE);
    }

    fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);

    if (-1 == fd) {
	    fprintf(stderr, "Cannot open '%s': %d, %s\n",
		     dev_name, errno, strerror(errno));
	    exit(EXIT_FAILURE);
    }
}

static void usage(FILE *fp, int argc, char **argv)
{
    fprintf(fp,
	     "Usage: %s [options]\n\n"
	     "Version 1.3\n"
	     "Options:\n"
	     "-d | --device name   Video device name [%s]\n"
	     "-h | --help          Print this message\n"
	     "-m | --mmap          Use memory mapped buffers [default]\n"
	     "-r | --read          Use read() calls\n"
	     "-u | --userp         Use application allocated buffers\n"
	     "-o | --output        Outputs stream to stdout\n"
	     "-f | --format        Force format to 640x480 YUYV\n"
	     "-c | --count         Number of frames to grab [%i]\n"
	     "",
	     argv[0], dev_name, frame_count);
}

static const char short_options[] = "d:hmruofc:";

static const struct option
long_options[] = {
    { "device", required_argument, NULL, 'd' },
    { "help",   no_argument,       NULL, 'h' },
    { "mmap",   no_argument,       NULL, 'm' },
    { "read",   no_argument,       NULL, 'r' },
    { "userp",  no_argument,       NULL, 'u' },
    { "output", no_argument,       NULL, 'o' },
    { "format", no_argument,       NULL, 'f' },
    { "count",  required_argument, NULL, 'c' },
    { 0, 0, 0, 0 }
};

int main(int argc, char **argv)
{
    dev_name = "/dev/video0";

    for (;;) {
	    int idx;
	    int c;

	    c = getopt_long(argc, argv,
			    short_options, long_options, &idx);

	    if (-1 == c)
		    break;

	    switch (c) {
	    case 0: /* getopt_long() flag */
		    break;

	    case 'd':
		    dev_name = optarg;
		    break;

	    case 'h':
		    usage(stdout, argc, argv);
		    exit(EXIT_SUCCESS);

	    case 'm':
		    io = IO_METHOD_MMAP;
		    break;

	    case 'r':
		    io = IO_METHOD_READ;
		    break;

	    case 'u':
		    io = IO_METHOD_USERPTR;
		    break;

	    case 'o':
		    out_buf++;
		    break;

	    case 'f':
		    force_format++;
		    break;

	    case 'c':
		    errno = 0;
		    frame_count = strtol(optarg, NULL, 0);
		    if (errno)
			    errno_exit(optarg);
		    break;

	    default:
		    usage(stderr, argc, argv);
		    exit(EXIT_FAILURE);
	    }
    }

    open_device();
    init_device();
    start_capturing();
    mainloop();
    stop_capturing();
    uninit_device();
    close_device();
    fprintf(stderr, "\n");
    return 0;
}