/// Wraps non-thread-safe capture device like a v4l webcam

use linuxvideo::
{
    format::
    {
        PixFormat,
        PixelFormat,
    },
    Device,
    stream::ReadStream,
};

pub struct Capture
{
    size_image: usize,
    stream: ReadStream,
}

impl Capture
{
    pub fn new () -> Result <Self, Error>
    {
        let x = Device::open ("/dev/video0")?;
        
        // sudo apt install v4l-utils
        // v4l2-ctl -d /dev/video0 --list-formats-ext
        
        let x = x.video_capture (PixFormat::new (1280, 720, PixelFormat::MJPG))?;
        let interval = x.set_frame_interval(linuxvideo::Fract::new(1, 30)).unwrap ();
        dbg! (interval);
        dbg! (x.format ());
        let size_image = usize::try_from (x.format ().size_image ()).unwrap ();
        let stream = x.into_stream ()?;
        
        Ok (Self 
        {
            size_image,
            stream,
        })
    }
    
    pub fn size_image (&self) -> usize
    {
        self.size_image
    }
    
    /// Blocks until the capture device gets us a frame
    
    pub fn wait_for_frame (&mut self, output: &mut [u8]) -> Result <usize, Error>
    {
        if output.len () < self.size_image ()
        {
            return Err (Error::OutputBufferTooSmall);
        }
        
        Ok (self.stream.dequeue (|view| 
        {
            let bytesused = usize::try_from (view.bytesused ()).unwrap ();
            let input = &view [0..bytesused];
            let _ = &mut output [0..bytesused].copy_from_slice (&input);
            Ok (input.len ())
        })?)
    }
    
    pub fn will_block (&self) -> std::io::Result <bool>
    {
        self.stream.will_block ()
    }
}

#[derive (Debug, thiserror::Error)]
pub enum Error
{
    #[error ("I/O")]
    Io (#[from] std::io::Error),
    #[error ("output buffer too small")]
    OutputBufferTooSmall,
}