use std::io::{self, Read};
use std::sync::mpsc;
use std::thread;

use sys::tty::get_tty;

/// Construct an asynchronous handle to the TTY standard input.
///
/// This allows you to read from standard input _without blocking_ the current thread.
/// Specifically, it works by firing up another thread to handle the event stream, which will then
/// be buffered in a mpsc queue, which will eventually be read by the current thread.
///
/// This will not read the piped standard input, but rather read from the TTY device, since reading
/// asyncronized from piped input would rarely make sense. In other words, if you pipe standard
/// output from another process, it won't be reflected in the stream returned by this function, as
/// this represents the TTY device, and not the piped standard input.
pub fn async_stdin() -> AsyncReader {
    let (send, recv) = mpsc::channel();

    thread::spawn(move || for i in get_tty().unwrap().bytes() {
                      if send.send(i).is_err() {
                          return;
                      }
                  });

    AsyncReader { recv: recv }
}

/// An asynchronous reader.
///
/// This acts as any other stream, with the exception that reading from it won't block. Instead,
/// the buffer will only be partially updated based on how much the internal buffer holds.
pub struct AsyncReader {
    /// The underlying mpsc receiver.
    recv: mpsc::Receiver<io::Result<u8>>,
}

// FIXME: Allow constructing an async reader from an arbitrary stream.

impl Read for AsyncReader {
    /// Read from the byte stream.
    ///
    /// This will never block, but try to drain the event queue until empty. If the total number of
    /// bytes written is lower than the buffer's length, the event queue is empty or that the event
    /// stream halted.
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let mut total = 0;

        loop {
            if total >= buf.len() {
                break;
            }

            match self.recv.try_recv() {
                Ok(Ok(b)) => {
                    buf[total] = b;
                    total += 1;
                }
                Ok(Err(e)) => return Err(e),
                Err(_) => break,
            }
        }

        Ok(total)
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use std::io::Read;

    #[test]
    fn test_async_stdin() {
        let stdin = async_stdin();
        stdin.bytes().next();
    }
}
