//! Clonable duplex byte streams that implement `futures_io` traits.
//!
//! `erl_dist` requires `AsyncRead + AsyncWrite + Unpin + Clone` on the carrier
//! (smol's `TcpStream` is clonable; iroh bi-streams and tokio-rustls streams are
//! not). We wrap any split read/write half in a shared duplex.
//!
//! Layout: `async_dup::Arc<async_dup::Mutex<Combined>>` — Arc is `Clone`, and
//! both Arc and Mutex forward futures-io traits when the inner type does.

use async_dup::{Arc as DupArc, Mutex as DupMutex};
use futures::io::{AsyncRead, AsyncWrite};
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};
use tokio::io::{AsyncRead as TokioRead, AsyncWrite as TokioWrite, ReadBuf};

/// A clonable futures-io duplex built from independent tokio read/write halves.
#[derive(Clone)]
pub struct DistStream {
    inner: DupArc<DupMutex<Combined>>,
}

/// Type-erased tokio read half.
type DynRead = Box<dyn TokioRead + Unpin + Send>;
/// Type-erased tokio write half.
type DynWrite = Box<dyn TokioWrite + Unpin + Send>;

struct Combined {
    read: DynRead,
    write: DynWrite,
}

impl DistStream {
    /// Wrap independent tokio async read/write halves.
    pub fn from_split<R, W>(read: R, write: W) -> Self
    where
        R: TokioRead + Unpin + Send + 'static,
        W: TokioWrite + Unpin + Send + 'static,
    {
        Self {
            inner: DupArc::new(DupMutex::new(Combined {
                read: Box::new(read),
                write: Box::new(write),
            })),
        }
    }

    /// Wrap a single tokio type that is both `AsyncRead` and `AsyncWrite`.
    pub fn from_rw<T>(stream: T) -> Self
    where
        T: TokioRead + TokioWrite + Unpin + Send + 'static,
    {
        let (read, write) = tokio::io::split(stream);
        Self::from_split(read, write)
    }
}

impl TokioRead for Combined {
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        Pin::new(&mut self.read).poll_read(cx, buf)
    }
}

impl TokioWrite for Combined {
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.write).poll_write(cx, buf)
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.write).poll_flush(cx)
    }

    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.write).poll_shutdown(cx)
    }
}

// Bridge tokio traits → futures_io for erl_dist.
impl AsyncRead for Combined {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<io::Result<usize>> {
        let mut read_buf = ReadBuf::new(buf);
        match TokioRead::poll_read(self, cx, &mut read_buf) {
            Poll::Ready(Ok(())) => Poll::Ready(Ok(read_buf.filled().len())),
            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
            Poll::Pending => Poll::Pending,
        }
    }
}

impl AsyncWrite for Combined {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        TokioWrite::poll_write(self, cx, buf)
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        TokioWrite::poll_flush(self, cx)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        TokioWrite::poll_shutdown(self, cx)
    }
}

impl AsyncRead for DistStream {
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut [u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.inner).poll_read(cx, buf)
    }
}

impl AsyncWrite for DistStream {
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.inner).poll_write(cx, buf)
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.inner).poll_flush(cx)
    }

    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.inner).poll_close(cx)
    }
}

impl std::fmt::Debug for DistStream {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("DistStream").finish_non_exhaustive()
    }
}