use crate::codec::decoder::Decoder;
use crate::codec::encoder::Encoder;

use tokio::{
    io::{AsyncRead, AsyncWrite},
    stream::Stream,
};

use bytes::BytesMut;
use futures_core::ready;
use futures_sink::Sink;
use log::trace;
use pin_project_lite::pin_project;
use std::borrow::{Borrow, BorrowMut};
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};

pin_project! {
    #[derive(Debug)]
    pub(crate) struct FramedImpl<T, U, State> {
        #[pin]
        pub(crate) inner: T,
        pub(crate) state: State,
        pub(crate) codec: U,
    }
}

const INITIAL_CAPACITY: usize = 8 * 1024;
const BACKPRESSURE_BOUNDARY: usize = INITIAL_CAPACITY;

pub(crate) struct ReadFrame {
    pub(crate) eof: bool,
    pub(crate) is_readable: bool,
    pub(crate) buffer: BytesMut,
}

pub(crate) struct WriteFrame {
    pub(crate) buffer: BytesMut,
}

#[derive(Default)]
pub(crate) struct RWFrames {
    pub(crate) read: ReadFrame,
    pub(crate) write: WriteFrame,
}

impl Default for ReadFrame {
    fn default() -> Self {
        Self {
            eof: false,
            is_readable: false,
            buffer: BytesMut::with_capacity(INITIAL_CAPACITY),
        }
    }
}

impl Default for WriteFrame {
    fn default() -> Self {
        Self {
            buffer: BytesMut::with_capacity(INITIAL_CAPACITY),
        }
    }
}

impl From<BytesMut> for ReadFrame {
    fn from(mut buffer: BytesMut) -> Self {
        let size = buffer.capacity();
        if size < INITIAL_CAPACITY {
            buffer.reserve(INITIAL_CAPACITY - size);
        }

        Self {
            buffer,
            is_readable: size > 0,
            eof: false,
        }
    }
}

impl From<BytesMut> for WriteFrame {
    fn from(mut buffer: BytesMut) -> Self {
        let size = buffer.capacity();
        if size < INITIAL_CAPACITY {
            buffer.reserve(INITIAL_CAPACITY - size);
        }

        Self { buffer }
    }
}

impl Borrow<ReadFrame> for RWFrames {
    fn borrow(&self) -> &ReadFrame {
        &self.read
    }
}
impl BorrowMut<ReadFrame> for RWFrames {
    fn borrow_mut(&mut self) -> &mut ReadFrame {
        &mut self.read
    }
}
impl Borrow<WriteFrame> for RWFrames {
    fn borrow(&self) -> &WriteFrame {
        &self.write
    }
}
impl BorrowMut<WriteFrame> for RWFrames {
    fn borrow_mut(&mut self) -> &mut WriteFrame {
        &mut self.write
    }
}
impl<T, U, R> Stream for FramedImpl<T, U, R>
where
    T: AsyncRead,
    U: Decoder,
    R: BorrowMut<ReadFrame>,
{
    type Item = Result<U::Item, U::Error>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        use crate::util::poll_read_buf;

        let mut pinned = self.project();
        let state: &mut ReadFrame = pinned.state.borrow_mut();
        loop {
            // Repeatedly call `decode` or `decode_eof` as long as it is
            // "readable". Readable is defined as not having returned `None`. If
            // the upstream has returned EOF, and the decoder is no longer
            // readable, it can be assumed that the decoder will never become
            // readable again, at which point the stream is terminated.
            if state.is_readable {
                if state.eof {
                    let frame = pinned.codec.decode_eof(&mut state.buffer)?;
                    return Poll::Ready(frame.map(Ok));
                }

                trace!("attempting to decode a frame");

                if let Some(frame) = pinned.codec.decode(&mut state.buffer)? {
                    trace!("frame decoded from buffer");
                    return Poll::Ready(Some(Ok(frame)));
                }

                state.is_readable = false;
            }

            assert!(!state.eof);

            // Otherwise, try to read more data and try again. Make sure we've
            // got room for at least one byte to read to ensure that we don't
            // get a spurious 0 that looks like EOF
            state.buffer.reserve(1);
            let bytect = match poll_read_buf(pinned.inner.as_mut(), cx, &mut state.buffer)? {
                Poll::Ready(ct) => ct,
                Poll::Pending => return Poll::Pending,
            };
            if bytect == 0 {
                state.eof = true;
            }

            state.is_readable = true;
        }
    }
}

impl<T, I, U, W> Sink<I> for FramedImpl<T, U, W>
where
    T: AsyncWrite,
    U: Encoder<I>,
    U::Error: From<io::Error>,
    W: BorrowMut<WriteFrame>,
{
    type Error = U::Error;

    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        if self.state.borrow().buffer.len() >= BACKPRESSURE_BOUNDARY {
            self.as_mut().poll_flush(cx)
        } else {
            Poll::Ready(Ok(()))
        }
    }

    fn start_send(self: Pin<&mut Self>, item: I) -> Result<(), Self::Error> {
        let pinned = self.project();
        pinned
            .codec
            .encode(item, &mut pinned.state.borrow_mut().buffer)?;
        Ok(())
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        use crate::util::poll_write_buf;
        trace!("flushing framed transport");
        let mut pinned = self.project();

        while !pinned.state.borrow_mut().buffer.is_empty() {
            let WriteFrame { buffer } = pinned.state.borrow_mut();
            trace!("writing; remaining={}", buffer.len());

            let n = ready!(poll_write_buf(pinned.inner.as_mut(), cx, buffer))?;

            if n == 0 {
                return Poll::Ready(Err(io::Error::new(
                    io::ErrorKind::WriteZero,
                    "failed to \
                     write frame to transport",
                )
                .into()));
            }
        }

        // Try flushing the underlying IO
        ready!(pinned.inner.poll_flush(cx))?;

        trace!("framed transport flushed");
        Poll::Ready(Ok(()))
    }

    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        ready!(self.as_mut().poll_flush(cx))?;
        ready!(self.project().inner.poll_shutdown(cx))?;

        Poll::Ready(Ok(()))
    }
}