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//! TCP server compatible with the official mobile and desktop application
use anyhow::{Context, Result};
use bytes::Bytes;
use futures::{channel::mpsc, pin_mut, Sink, SinkExt, Stream, StreamExt, TryStreamExt};
use tokio::{
    io::{AsyncRead, AsyncWrite},
    net::{TcpListener, ToSocketAddrs},
    select,
    sync::broadcast,
};
use tokio_util::codec::Framed;

use crate::{transport::net::Codec, utils::OwnedJoinHandle, MiniDSPError};

/// Forwards the given tcp stream to a transport.
/// This lets multiple users talk to the same device simultaneously, which depending on the
/// user could be problematic.
async fn forward<T>(
    tcp: T,
    mut device_tx: mpsc::Sender<Bytes>,
    mut device_rx: broadcast::Receiver<Bytes>,
) -> Result<()>
where
    T: AsyncRead + AsyncWrite + 'static,
{
    // Apply framing to the TCP stream
    let remote = Framed::new(tcp, Codec::new_server());

    pin_mut!(remote);

    loop {
        select! {
            frame = device_rx.recv() => {
                remote.send(frame?).await.context("remote.send failed")?;
            },
            frame = remote.next() => {
                let frame = frame.ok_or(MiniDSPError::TransportClosed)?;
                device_tx.send(frame.context("decoding frame")?).await.context("device_tx.send failed")?;
            },
        }
    }
}

/// Listen and forward every incoming tcp connection to the given transport
pub async fn serve<A, T, E>(bind_address: A, transport: T) -> Result<()>
where
    A: ToSocketAddrs,
    T: Sink<Bytes, Error = E> + Stream<Item = Result<Bytes, E>> + Send + 'static,
    E: Into<anyhow::Error> + Send + 'static,
{
    // Setup a channel-based forwarder so we can multiplex multiple clients. This could do
    // command-level multiplexing eventually.

    let (sink, stream) = transport.split();
    let (sink_tx, mut sink_rx) = mpsc::channel::<Bytes>(10);
    let (stream_tx, mut stream_rx) = broadcast::channel::<Bytes>(10);

    // Truncate each HID frame after its ending
    let stream = stream.err_into().map(|frame| {
        let frame = frame?;
        if frame.is_empty() {
            return Err(MiniDSPError::MalformedResponse(
                "Received an empty frame".to_string(),
            ));
        }

        let len = frame[0] as usize;
        if frame.len() < len {
            return Err(MiniDSPError::MalformedResponse(format!(
                "Expected frame of length {}, got {}",
                len,
                frame.len()
            )));
        }

        Ok::<_, MiniDSPError>(frame.slice(0..len))
    });

    // Receive
    let mut rx_handle = {
        let stream_tx = stream_tx.clone();
        let mut stream = Box::pin(stream);
        let handle = tokio::spawn(async move {
            while let Some(frame) = stream.next().await {
                if let Ok(frame) = frame {
                    if let Err(e) = stream_tx.send(frame) {
                        log::error!("stream tx failed: {:?}", e);
                    }
                }
            }
            Ok::<(), E>(())
        });
        OwnedJoinHandle::new(handle)
    };

    // Send
    let mut tx_handle = {
        let mut sink = Box::pin(sink);
        let handle = tokio::spawn(async move {
            while let Some(frame) = sink_rx.next().await {
                sink.send(frame).await?;
            }
            Ok::<_, E>(())
        });
        OwnedJoinHandle::new(handle)
    };

    let listener = TcpListener::bind(bind_address).await?;
    loop {
        select! {
           result = &mut tx_handle => {
               let result = result.expect("tx joinhandle");
               if let Err(e) = result {
                   log::error!("tx error: {}", e.into());
               }
           }
           result = &mut rx_handle => {
                let result = result.expect("rx joinhandle");
                if let Err(e) = result {
                    log::error!("rx error: {}", e.into());
                }
            }
           result = listener.accept() => {
                let (stream, addr) = result?;
                log::info!("[{:?}] New connection", addr);

                let device_tx = sink_tx.clone();
                let device_rx = stream_tx.clone().subscribe();

                tokio::spawn(async move {
                    let result = forward(stream, device_tx, device_rx).await;

                    if let Err(e) = result {
                        log::info!("[{}] Connection closed: {:?}", addr, e);
                    }

                    log::info!("[{:?}] Closed", addr);
                });
           },
           result = stream_rx.recv() => {
                if result.is_err() {
                    log::error!("stream rx: {:?}", &result);
                    return Err(MiniDSPError::TransportClosed.into())
                }
           }
        }
    }
}