// Copyright 2024 The NativeLink Authors. All rights reserved.

//

// Licensed under the Functional Source License, Version 1.1, Apache 2.0 Future License (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//    See LICENSE file for details

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

use core::pin::Pin;

use core::sync::atomic::{AtomicBool, Ordering};

use core::task::Poll;

use std::collections::VecDeque;

use std::sync::Arc;

use bytes::{Bytes, BytesMut};

use futures::task::Context;

use futures::{Future, Stream, TryFutureExt};

use nativelink_error::{Code, Error, ResultExt, error_if, make_err, make_input_err};

use tokio::sync::mpsc;

use tracing::warn;

const ZERO_DATA: Bytes = Bytes::new();

/// Create a channel pair that can be used to transport buffer objects around to

/// different components. This wrapper is used because the streams give some

/// utility like managing EOF in a more friendly way, ensure if no EOF is received

/// it will send an error to the receiver channel before shutting down and count

/// the number of bytes sent.

#[must_use]

pub fn make_buf_channel_pair() -> (DropCloserWriteHalf, DropCloserReadHalf) {

    // We allow up to 2 items in the buffer at any given time. There is no major

    // reason behind this magic number other than thinking it will be nice to give

    // a little time for another thread to wake up and consume data if another

    // thread is pumping large amounts of data into the channel.

    let (tx, rx) = mpsc::channel(2);

    let eof_sent = Arc::new(AtomicBool::new(false));

    (

        DropCloserWriteHalf {

            tx: Some(tx),

            bytes_written: 0,

            eof_sent: eof_sent.clone(),

        },

        DropCloserReadHalf {

            rx,

            queued_data: VecDeque::new(),

            last_err: None,

            eof_sent,

            bytes_received: 0,

            recent_data: Vec::new(),

            max_recent_data_size: 0,

        },

    )

}

/// Writer half of the pair.

#[derive(Debug)]

pub struct DropCloserWriteHalf {

    tx: Option<mpsc::Sender<Bytes>>,

    bytes_written: u64,

    eof_sent: Arc<AtomicBool>,

}

impl DropCloserWriteHalf {

    /// Sends data over the channel to the receiver.

    pub fn send(&mut self, buf: Bytes) -> impl Future<Output = Result<(), Error>> + '_ {

        self.send_get_bytes_on_error(buf).map_err(|err| err.0)

    }

    /// Sends data over the channel to the receiver.

    #[inline]

    async fn send_get_bytes_on_error(&mut self, buf: Bytes) -> Result<(), (Error, Bytes)> {

        let tx = match self

            .tx

            .as_ref()

            .ok_or_else(|| 
make_err!0
(
Code::Internal0
, "Tried to send while stream is closed"))

        {

            Ok(tx) => tx,

            Err(e) => return Err((e, buf)),

        };

        let Ok(buf_len) = u64::try_from(buf.len()) else {

            return Err((

                make_err!(Code::Internal, "Could not convert usize to u64"),

                buf,

            ));

        };

        if buf_len == 0 {

            return Err((

                make_input_err!("Cannot send EOF in send(). Instead use send_eof()"),

                buf,

            ));

        }

        if let Err(
err0
) = tx.send(buf).await {

            // Close our channel.

            self.tx = None;

            return Err((

                make_err!(

                    Code::Internal,

                    "Failed to write to data, receiver disconnected"

                ),

                err.0,

            ));

        }

        self.bytes_written += buf_len;

        Ok(())

    }

    /// Binds a reader and a writer together. This will send all the data from the reader

    /// to the writer until an EOF is received.

    /// This will always read one message ahead to ensure that if an error happens

    /// on the EOF message it will not forward on the last payload message and instead

    /// forward on the error.

    pub async fn bind_buffered(&mut self, reader: &mut DropCloserReadHalf) -> Result<(), Error> {

        loop {

            let chunk = reader

                .recv()

                .await

                .err_tip(|| "In DropCloserWriteHalf::bind_buffered::recv")
?0
;

            if chunk.is_empty() {

                self.send_eof()

                    .err_tip(|| "In DropCloserWriteHalf::bind_buffered::send_eof")
?0
;

                break; // EOF.

            }

            // Always read one message ahead so if we get an error on our EOF

            // we forward it on to the reader.

            if reader.peek().await.is_err() {

                // Read our next message for good book keeping.

                drop(

                    reader

                        .recv()

                        .await

                        .err_tip(|| "In DropCloserWriteHalf::bind_buffered::peek::eof")?,

                );

                return Err(make_err!(

                    Code::Internal,

                    "DropCloserReadHalf::peek() said error, but when data received said Ok. This should never happen."

                ));

            }

            match self.send_get_bytes_on_error(chunk).await {

                Ok(()) => {}

                Err(e) => {

                    reader.queued_data.push_front(e.1);

                    return Err(e.0).err_tip(|| "In DropCloserWriteHalf::bind_buffered::send");

                }

            }

        }

        Ok(())

    }

    /// Sends an EOF (End of File) message to the receiver which will gracefully let the

    /// stream know it has no more data. This will close the stream.

    pub fn send_eof(&mut self) -> Result<(), Error> {

        // Flag that we have sent the EOF.

        let eof_was_sent = self.eof_sent.swap(true, Ordering::Release);

        if eof_was_sent {

            warn!(

                "Stream already closed when eof already was sent. This is often ok for retry was triggered, but should not happen on happy path."

            );

            return Ok(());

        }

        // Now close our stream.

        self.tx = None;

        Ok(())

    }

    /// Returns the number of bytes written so far. This does not mean the receiver received

    /// all of the bytes written to the stream so far.

    #[must_use]

    pub const fn get_bytes_written(&self) -> u64 {

        self.bytes_written

    }

    /// Returns if the pipe was broken. This is good for determining if the reader broke the

    /// pipe or the writer broke the pipe, since this will only return true if the pipe was

    /// broken by the writer.

    #[must_use]

    pub const fn is_pipe_broken(&self) -> bool {

        self.tx.is_none()

    }

}

/// Reader half of the pair.

#[derive(Debug)]

pub struct DropCloserReadHalf {

    rx: mpsc::Receiver<Bytes>,

    /// Number of bytes received over the stream.

    bytes_received: u64,

    eof_sent: Arc<AtomicBool>,

    /// If there was an error in the stream, this will be set to the last error.

    last_err: Option<Error>,

    /// If not empty, this is the data that needs to be sent out before

    /// data from the underlying channel can should be sent.

    queued_data: VecDeque<Bytes>,

    /// As data is being read from the stream, this buffer will be filled

    /// with the most recent data. Once `max_recent_data_size` is reached

    /// this buffer will be cleared and no longer be populated.

    /// This is useful if the caller wants to reset the the reader to before

    /// any of the data was received if possible (eg: something failed and

    /// we want to retry).

    recent_data: Vec<Bytes>,

    /// Amount of data to keep in the `recent_data` buffer before clearing it

    /// and no longer populating it.

    max_recent_data_size: u64,

}

impl DropCloserReadHalf {

    /// Returns if the stream has data ready.

    pub fn is_empty(&self) -> bool {

        self.rx.is_empty()

    }

    fn recv_inner(&mut self, chunk: Bytes) -> Result<Bytes, Error> {

        // `queued_data` is allowed to have empty bytes that represent EOF

        if chunk.is_empty() {

            if !self.eof_sent.load(Ordering::Acquire) {

                let err = make_err!(Code::Internal, "Sender dropped before sending EOF");

                self.queued_data.clear();

                self.recent_data.clear();

                self.bytes_received = 0;

                self.last_err = Some(err.clone());

                return Err(err);

            }

            self.maybe_populate_recent_data(&ZERO_DATA);

            return Ok(ZERO_DATA);

        }

        self.bytes_received += chunk.len() as u64;

        self.maybe_populate_recent_data(&chunk);

        Ok(chunk)

    }

    /// Try to receive a chunk of data, returning `None` if none is available.

    pub fn try_recv(&mut self) -> Option<Result<Bytes, Error>> {

        if let Some(
err2
) = &self.last_err {

            return Some(Err(err.clone()));

        }

        self.queued_data.pop_front().map(Ok)

    }

    /// Receive a chunk of data, waiting asynchronously until some is available.

    pub async fn recv(&mut self) -> Result<Bytes, Error> {

        if let Some(
result23.7k
) = self.try_recv() {

            result

        } else {

            // `None` here indicates EOF, which we represent as Zero data

            let 
data145k
 = self.rx.recv().await.
unwrap_or145k
(
ZERO_DATA145k
);

            self.recv_inner(data)

        }

    }

    fn maybe_populate_recent_data(&mut self, chunk: &Bytes) {

        if self.max_recent_data_size == 0 {

            return; // Fast path.

        }

        if self.bytes_received > self.max_recent_data_size {

            if !self.recent_data.is_empty() {

                self.recent_data.clear();

            }

            return;

        }

        self.recent_data.push(chunk.clone());

    }

    /// Sets the maximum size of the `recent_data` buffer. If the number of bytes

    /// received exceeds this size, the `recent_data` buffer will be cleared and

    /// no longer populated.

    pub const fn set_max_recent_data_size(&mut self, size: u64) {

        self.max_recent_data_size = size;

    }

    /// Attempts to reset the stream to before any data was received. This will

    /// only work if the number of bytes received is less than `max_recent_data_size`.

    ///

    /// On error the state of the stream is undefined and the caller should not

    /// attempt to use the stream again.

    pub fn try_reset_stream(&mut self) -> Result<(), Error> {

        if self.bytes_received > self.max_recent_data_size {

            return Err(make_err!(

                Code::Internal,

                "Cannot reset stream, max_recent_data_size exceeded"

            ));

        }

        let mut data_sum = 0;

        for 
chunk0
 in self.recent_data.drain(..).rev() {

            data_sum += chunk.len() as u64;

            self.queued_data.push_front(chunk);

        }

        assert!(self.recent_data.is_empty(), "Recent_data should be empty");

        // Ensure the sum of the bytes in recent_data is equal to the bytes_received.

        error_if!(

            data_sum != self.bytes_received,

            "Sum of recent_data bytes does not equal bytes_received"

        );

        self.bytes_received = 0;

        Ok(())

    }

    /// Drains the reader until an EOF is received, but sends data to the void.

    pub async fn drain(&mut self) -> Result<(), Error> {

        loop {

            if self

                .recv()

                .await

                .err_tip(|| "Failed to drain in buf_channel::drain")
?0

                .is_empty()

            {

                break; // EOF.

            }

        }

        Ok(())

    }

    /// Peek the next set of bytes in the stream without consuming them.

    pub async fn peek(&mut self) -> Result<&Bytes, Error> {

        if self.queued_data.is_empty() {

            let 
chunk13.1k
 = self.recv().await.err_tip(|| "In buf_channel::peek")
?5
;

            self.queued_data.push_front(chunk);

        }

        Ok(self

            .queued_data

            .front()

            .expect("Should have data in the queue"))

    }

    /// The number of bytes received over this stream so far.

    pub const fn get_bytes_received(&self) -> u64 {

        self.bytes_received

    }

    /// Takes exactly `size` number of bytes from the stream and returns them.

    /// This means the stream will keep polling until either an EOF is received or

    /// `size` bytes are received and concat them all together then return them.

    /// This method is optimized to reduce copies when possible.

    /// If `size` is None, it will take all the bytes in the stream.

    pub async fn consume(&mut self, size: Option<usize>) -> Result<Bytes, Error> {

        let size = size.unwrap_or(usize::MAX);

        let first_chunk = {

            let 
mut chunk34.1k
 = self

                .recv()

                .await

                .err_tip(|| "During first read of buf_channel::take()")
?18
;

            if chunk.is_empty() {

                return Ok(chunk); // EOF.

            }

            if chunk.len() > size {

                let remaining = chunk.split_off(size);

                self.queued_data.push_front(remaining);

                // No need to read EOF if we are a partial chunk.

                return Ok(chunk);

            }

            // Try to read our EOF to ensure our sender did not error out.

            match self.peek().await {

                Ok(peeked_chunk) => {

                    if peeked_chunk.is_empty() || 
chunk1.84k
.len() == size {

                        return Ok(chunk);

                    }

                }

                Err(e) => {

                    return Err(e).err_tip(|| "Failed to check if next chunk is EOF")?;

                }

            }

            chunk

        };

        let mut output = BytesMut::new();

        output.extend_from_slice(&first_chunk);

        loop {

            let 
mut chunk120k
 = self

                .recv()

                .await

                .err_tip(|| "During next read of buf_channel::take()")
?1
;

            if chunk.is_empty() {

                break; // EOF.

            }

            if output.len() + chunk.len() > size {

                // Slice off the extra data and put it back into the queue. We are done.

                let remaining = chunk.split_off(size - output.len());

                self.queued_data.push_front(remaining);

            }

            output.extend_from_slice(&chunk);

            if output.len() == size {

                break; // We are done.

            }

        }

        Ok(output.freeze())

    }

}

impl Stream for DropCloserReadHalf {

    type Item = Result<Bytes, std::io::Error>;

    // TODO(palfrey) This is not very efficient as we are creating a new future on every

    // poll() call. It might be better to use a waker.

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

        Box::pin(self.recv())

            .as_mut()

            .poll(cx)

            .map(|result| match 
result98
 {

                Ok(bytes) => {

                    if bytes.is_empty() {

                        return None;

                    }

                    Some(Ok(bytes))

                }

                Err(e) => Some(Err(e.to_std_err())),

            })

    }

}