use crate::lock::BiLock;

use core::fmt;

use futures_core::ready;

use futures_core::task::{Context, Poll};

use futures_io::{AsyncRead, AsyncWrite, IoSlice, IoSliceMut};

use std::io;

use std::pin::Pin;

/// The readable half of an object returned from `AsyncRead::split`.

#[derive(Debug)]

pub struct ReadHalf<T> {

    handle: BiLock<T>,

}

/// The writable half of an object returned from `AsyncRead::split`.

#[derive(Debug)]

pub struct WriteHalf<T> {

    handle: BiLock<T>,

}

fn lock_and_then<T, U, E, F>(lock: &BiLock<T>, cx: &mut Context<'_>, f: F) -> Poll<Result<U, E>>

where

    F: FnOnce(Pin<&mut T>, &mut Context<'_>) -> Poll<Result<U, E>>,

{

    let mut l = ready!(lock.poll_lock(cx));

    f(l.as_pin_mut(), cx)

}

pub(super) fn split<T: AsyncRead + AsyncWrite>(t: T) -> (ReadHalf<T>, WriteHalf<T>) {

    let (a, b) = BiLock::new(t);

    (ReadHalf { handle: a }, WriteHalf { handle: b })

}

impl<T: Unpin> ReadHalf<T> {

    /// Attempts to put the two "halves" of a split `AsyncRead + AsyncWrite` back

    /// together. Succeeds only if the `ReadHalf<T>` and `WriteHalf<T>` are

    /// a matching pair originating from the same call to `AsyncReadExt::split`.

    pub fn reunite(self, other: WriteHalf<T>) -> Result<T, ReuniteError<T>> {

        self.handle

            .reunite(other.handle)

            .map_err(|err| ReuniteError(ReadHalf { handle: err.0 }, WriteHalf { handle: err.1 }))

    }

}

impl<T: Unpin> WriteHalf<T> {

    /// Attempts to put the two "halves" of a split `AsyncRead + AsyncWrite` back

    /// together. Succeeds only if the `ReadHalf<T>` and `WriteHalf<T>` are

    /// a matching pair originating from the same call to `AsyncReadExt::split`.

    pub fn reunite(self, other: ReadHalf<T>) -> Result<T, ReuniteError<T>> {

        other.reunite(self)

    }

}

impl<R: AsyncRead> AsyncRead for ReadHalf<R> {

    fn poll_read(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &mut [u8],

    ) -> Poll<io::Result<usize>> {

        lock_and_then(&self.handle, cx, |l, cx| l.poll_read(cx, buf))

    }

    fn poll_read_vectored(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        bufs: &mut [IoSliceMut<'_>],

    ) -> Poll<io::Result<usize>> {

        lock_and_then(&self.handle, cx, |l, cx| l.poll_read_vectored(cx, bufs))

    }

}

impl<W: AsyncWrite> AsyncWrite for WriteHalf<W> {

    fn poll_write(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &[u8],

    ) -> Poll<io::Result<usize>> {

        lock_and_then(&self.handle, cx, |l, cx| l.poll_write(cx, buf))

    }

    fn poll_write_vectored(

        self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        bufs: &[IoSlice<'_>],

    ) -> Poll<io::Result<usize>> {

        lock_and_then(&self.handle, cx, |l, cx| l.poll_write_vectored(cx, bufs))

    }

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

        lock_and_then(&self.handle, cx, |l, cx| l.poll_flush(cx))

    }

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

        lock_and_then(&self.handle, cx, |l, cx| l.poll_close(cx))

    }

}

/// Error indicating a `ReadHalf<T>` and `WriteHalf<T>` were not two halves

/// of a `AsyncRead + AsyncWrite`, and thus could not be `reunite`d.

pub struct ReuniteError<T>(pub ReadHalf<T>, pub WriteHalf<T>);

impl<T> fmt::Debug for ReuniteError<T> {

    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

        f.debug_tuple("ReuniteError").field(&"...").finish()

    }

}

impl<T> fmt::Display for ReuniteError<T> {

    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

        write!(f, "tried to reunite a ReadHalf and WriteHalf that don't form a pair")

    }

}

#[cfg(feature = "std")]

impl<T: core::any::Any> std::error::Error for ReuniteError<T> {}