// Copyright (c) 2013-2016 Sandstorm Development Group, Inc. and contributors
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

//! Asynchronous reading and writing of messages using the
//! [standard stream framing](https://capnproto.org/encoding.html#serialization-over-a-stream).

use std::convert::TryInto;

use capnp::{message, Error, Result, Word, OutputSegments};

use futures::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};

pub struct OwnedSegments {
    segment_slices: Vec<(usize, usize)>,
    owned_space: Vec<Word>,
}

impl message::ReaderSegments for OwnedSegments {
    fn get_segment<'a>(&'a self, id: u32) -> Option<&'a [Word]> {
        if id < self.segment_slices.len() as u32 {
            let (a, b) = self.segment_slices[id as usize];
            Some(&self.owned_space[a..b])
        } else {
            None
        }
    }
}

/// Begins an asynchronous read of a message from `reader`.
pub async fn read_message<R>(mut reader: R, options: message::ReaderOptions) -> Result<Option<message::Reader<OwnedSegments>>>
    where R: AsyncRead + Unpin
{
    let (total_words, segment_slices) = match read_segment_table(&mut reader, options).await? {
        Some(s) => s,
        None => return Ok(None),
    };
    Ok(Some(read_segments(reader, total_words, segment_slices, options).await?))
}

async fn read_segment_table<R>(mut reader: R,
                               options: message::ReaderOptions)
                               -> Result<Option<(usize, Vec<(usize, usize)>)>>
    where R: AsyncRead + Unpin
{
    let mut buf: [u8; 8] = [0; 8];
    {
        let n = reader.read(&mut buf[..]).await?;
        if n == 0 {
            return Ok(None)
        } else if n < 8 {
            reader.read_exact(&mut buf[n..]).await?;
        }
    }
    let (segment_count, first_segment_length) = parse_segment_table_first(&buf[..])?;

    let mut segment_slices: Vec<(usize, usize)> = Vec::with_capacity(segment_count);
    segment_slices.push((0,first_segment_length));
    let mut total_words = first_segment_length;

    if segment_count > 1 {
        if segment_count < 4 {
            // small enough that we can reuse our existing buffer
            reader.read_exact(&mut buf).await?;
            for idx in 0..(segment_count - 1) {
                let segment_len =
                    u32::from_le_bytes(buf[(idx * 4)..(idx + 1) * 4].try_into().unwrap()) as usize;

                segment_slices.push((total_words, total_words + segment_len));
                total_words += segment_len;

            }
        } else {
            let mut segment_sizes = vec![0u8; (segment_count & !1) * 4];
            reader.read_exact(&mut segment_sizes[..]).await?;
            for idx in 0..(segment_count - 1) {
                let segment_len =
                    u32::from_le_bytes(segment_sizes[(idx * 4)..(idx + 1) * 4].try_into().unwrap()) as usize;

                segment_slices.push((total_words, total_words + segment_len));
                total_words += segment_len;
            }
        }
    }

    // Don't accept a message which the receiver couldn't possibly traverse without hitting the
    // traversal limit. Without this check, a malicious client could transmit a very large segment
    // size to make the receiver allocate excessive space and possibly crash.
    if total_words as u64 > options.traversal_limit_in_words  {
        return Err(Error::failed(
            format!("Message has {} words, which is too large. To increase the limit on the \
             receiving end, see capnp::message::ReaderOptions.", total_words)))
    }

    Ok(Some((total_words, segment_slices)))
}

/// Reads segments from `read`.
async fn read_segments<R>(mut read: R,
                    total_words: usize,
                    segment_slices: Vec<(usize, usize)>,
                    options: message::ReaderOptions)
                    -> Result<message::Reader<OwnedSegments>>
    where R: AsyncRead + Unpin
{
    let mut owned_space: Vec<Word> = Word::allocate_zeroed_vec(total_words);
    read.read_exact(Word::words_to_bytes_mut(&mut owned_space[..])).await?;
    let segments = OwnedSegments {segment_slices: segment_slices, owned_space: owned_space};
    Ok(message::Reader::new(segments, options))
}

/// Parses the first word of the segment table.
///
/// The segment table format for streams is defined in the Cap'n Proto
/// [encoding spec](https://capnproto.org/encoding.html#serialization-over-a-stream)
///
/// Returns the segment count and first segment length, or a state if the
/// read would block.
fn parse_segment_table_first(buf: &[u8]) -> Result<(usize, usize)>
{
    let segment_count = u32::from_le_bytes(buf[0..4].try_into().unwrap()).wrapping_add(1);
    if segment_count >= 512 {
        return Err(Error::failed(format!("Too many segments: {}", segment_count)))
    } else if segment_count == 0 {
        return Err(Error::failed(format!("Too few segments: {}", segment_count)))
    }

    let first_segment_len = u32::from_le_bytes(buf[4..8].try_into().unwrap());
    Ok((segment_count as usize, first_segment_len as usize))
}

/// Something that contains segments ready to be written out.
pub trait AsOutputSegments {
    fn as_output_segments<'a>(&'a self) -> OutputSegments<'a>;
}


impl <'a, M> AsOutputSegments for &'a M where M: AsOutputSegments {
    fn as_output_segments<'b>(&'b self) -> OutputSegments<'b> {
        (*self).as_output_segments()
    }
}

impl <A> AsOutputSegments for message::Builder<A> where A: message::Allocator {
    fn as_output_segments<'a>(&'a self) -> OutputSegments<'a> {
        self.get_segments_for_output()
    }
}

/*impl <'a, A> AsOutputSegments for &'a message::Builder<A> where A: message::Allocator {
    fn as_output_segments<'b>(&'b self) -> OutputSegments<'b> {
        self.get_segments_for_output()
    }
}*/

impl <A> AsOutputSegments for ::std::rc::Rc<message::Builder<A>> where A: message::Allocator {
    fn as_output_segments<'a>(&'a self) -> OutputSegments<'a> {
        self.get_segments_for_output()
    }
}

/// Writes the provided message to `writer`. Does not call `flush()`.
pub async fn write_message<W,M>(mut writer: W, message: M) -> Result<()>
    where W: AsyncWrite + Unpin, M: AsOutputSegments
{
    let segments = message.as_output_segments();
    write_segment_table(&mut writer, &segments[..]).await?;
    write_segments(writer, &segments[..]).await?;
    Ok(())
}

async fn write_segment_table<W>(mut write: W, segments: &[&[Word]]) -> ::std::io::Result<()>
    where W: AsyncWrite + Unpin
{
    let mut buf: [u8; 8] = [0; 8];
    let segment_count = segments.len();

    // write the first Word, which contains segment_count and the 1st segment length
    buf[0..4].copy_from_slice(&(segment_count as u32 - 1).to_le_bytes());
    buf[4..8].copy_from_slice(&(segments[0].len() as u32).to_le_bytes());
    write.write_all(&buf).await?;

    if segment_count > 1 {
        if segment_count < 4 {
            for idx in 1..segment_count {
                buf[(idx - 1) * 4..idx * 4].copy_from_slice(
                    &(segments[idx].len() as u32).to_le_bytes());
            }
            if segment_count == 2 {
                for idx in 4..8 { buf[idx] = 0 }
            }
            write.write_all(&buf).await?;
        } else {
            let mut buf = vec![0; (segment_count & !1) * 4];
            for idx in 1..segment_count {
                buf[(idx - 1) * 4..idx * 4].copy_from_slice(
                    &(segments[idx].len() as u32).to_le_bytes());
            }
            if segment_count % 2 == 0 {
                for idx in (buf.len() - 4)..(buf.len()) { buf[idx] = 0 }
            }
            write.write_all(&buf).await?;
        }
    }
    Ok(())
}

/// Writes segments to `write`.
async fn write_segments<W>(mut write: W, segments: &[&[Word]]) -> Result<()>
    where W: AsyncWrite + Unpin
{
    for i in 0..segments.len() {
        write.write_all(Word::words_to_bytes(segments[i])).await?;
    }
    Ok(())
}



#[cfg(test)]
pub mod test {
    use std::cmp;
    use std::io::{self, Read, Write};
    use std::pin::Pin;
    use std::task::{Context, Poll};

    use futures::{AsyncRead, AsyncWrite};
    use futures::io::Cursor;

    use quickcheck::{quickcheck, TestResult};

    use capnp::{Word, message, OutputSegments};
    use capnp::message::ReaderSegments;

    use super::{
        AsOutputSegments,
        read_message,
        read_segment_table,
        write_message,
    };

    #[test]
    fn test_read_segment_table() {
        let mut exec = futures::executor::LocalPool::new();
        let mut buf = vec![];

        buf.extend([0,0,0,0, // 1 segments
                    0,0,0,0] // 0 length
                    .iter().cloned());
        let (words, segment_slices) = exec.run_until(read_segment_table(Cursor::new(&buf[..]),
                                                                        message::ReaderOptions::new())).unwrap().unwrap();
        assert_eq!(0, words);
        assert_eq!(vec![(0,0)], segment_slices);
        buf.clear();

        buf.extend([0,0,0,0, // 1 segments
                    1,0,0,0] // 1 length
                   .iter().cloned());

        let (words, segment_slices) = exec.run_until(read_segment_table(&mut Cursor::new(&buf[..]),
                                                                        message::ReaderOptions::new())).unwrap().unwrap();
        assert_eq!(1, words);
        assert_eq!(vec![(0,1)], segment_slices);
        buf.clear();

        buf.extend([1,0,0,0, // 2 segments
                    1,0,0,0, // 1 length
                    1,0,0,0, // 1 length
                    0,0,0,0] // padding
                    .iter().cloned());
        let (words, segment_slices) = exec.run_until(read_segment_table(&mut Cursor::new(&buf[..]),
                                                                        message::ReaderOptions::new())).unwrap().unwrap();
        assert_eq!(2, words);
        assert_eq!(vec![(0,1), (1, 2)], segment_slices);
        buf.clear();

        buf.extend([2,0,0,0, // 3 segments
                    1,0,0,0, // 1 length
                    1,0,0,0, // 1 length
                    0,1,0,0] // 256 length
                    .iter().cloned());
        let (words, segment_slices) = exec.run_until(read_segment_table(&mut Cursor::new(&buf[..]),
                                                                        message::ReaderOptions::new())).unwrap().unwrap();
        assert_eq!(258, words);
        assert_eq!(vec![(0,1), (1, 2), (2, 258)], segment_slices);
        buf.clear();

        buf.extend([3,0,0,0,  // 4 segments
                    77,0,0,0, // 77 length
                    23,0,0,0, // 23 length
                    1,0,0,0,  // 1 length
                    99,0,0,0, // 99 length
                    0,0,0,0]  // padding
                    .iter().cloned());
        let (words, segment_slices) = exec.run_until(read_segment_table(&mut Cursor::new(&buf[..]),
                                                                        message::ReaderOptions::new())).unwrap().unwrap();
        assert_eq!(200, words);
        assert_eq!(vec![(0,77), (77, 100), (100, 101), (101, 200)], segment_slices);
        buf.clear();
    }

    #[test]
    fn test_read_invalid_segment_table() {
        let mut exec = futures::executor::LocalPool::new();
        let mut buf = vec![];

        buf.extend([0,2,0,0].iter().cloned()); // 513 segments
        buf.extend([0; 513 * 4].iter().cloned());
        assert!(exec.run_until(read_segment_table(Cursor::new(&buf[..]),
                                                  message::ReaderOptions::new())).is_err());
        buf.clear();

        buf.extend([0,0,0,0].iter().cloned()); // 1 segments
        assert!(exec.run_until(read_segment_table(Cursor::new(&buf[..]),
                                                  message::ReaderOptions::new())).is_err());

        buf.clear();

        buf.extend([0,0,0,0].iter().cloned()); // 1 segments
        buf.extend([0; 3].iter().cloned());
        assert!(exec.run_until(read_segment_table(Cursor::new(&buf[..]),
                                                  message::ReaderOptions::new())).is_err());
        buf.clear();

        buf.extend([255,255,255,255].iter().cloned()); // 0 segments
        assert!(exec.run_until(read_segment_table(Cursor::new(&buf[..]),
                                                  message::ReaderOptions::new())).is_err());
        buf.clear();
    }

    fn construct_segment_table(segments: &[&[Word]]) -> Vec<u8> {
        let mut exec = futures::executor::LocalPool::new();
        let mut buf = vec![];
        exec.run_until(super::write_segment_table(&mut buf, segments)).unwrap();
        buf
    }

    #[test]
    fn test_construct_segment_table() {

        let segment_0: [Word; 0] = [];
        let segment_1 = [capnp::word(1,0,0,0,0,0,0,0); 1];
        let segment_199 = [capnp::word(199,0,0,0,0,0,0,0); 199];

        let buf = construct_segment_table(&[&segment_0]);
        assert_eq!(&[0,0,0,0,  // 1 segments
                     0,0,0,0], // 0 length
                   &buf[..]);

        let buf = construct_segment_table(&[&segment_1]);
        assert_eq!(&[0,0,0,0,  // 1 segments
                     1,0,0,0], // 1 length
                   &buf[..]);

        let buf = construct_segment_table(&[&segment_199]);
        assert_eq!(&[0,0,0,0,    // 1 segments
                     199,0,0,0], // 199 length
                   &buf[..]);

        let buf = construct_segment_table(&[&segment_0, &segment_1]);
        assert_eq!(&[1,0,0,0,  // 2 segments
                     0,0,0,0,  // 0 length
                     1,0,0,0,  // 1 length
                     0,0,0,0], // padding
                   &buf[..]);

        let buf = construct_segment_table(&[&segment_199, &segment_1, &segment_199, &segment_0]);
        assert_eq!(&[3,0,0,0,   // 4 segments
                     199,0,0,0, // 199 length
                     1,0,0,0,   // 1 length
                     199,0,0,0, // 199 length
                     0,0,0,0,   // 0 length
                     0,0,0,0],  // padding
                   &buf[..]);

        let buf = construct_segment_table(
            &[&segment_199, &segment_1, &segment_199, &segment_0, &segment_1]);
        assert_eq!(&[4,0,0,0,   // 5 segments
                     199,0,0,0, // 199 length
                     1,0,0,0,   // 1 length
                     199,0,0,0, // 199 length
                     0,0,0,0,   // 0 length
                     1,0,0,0],  // 1 length
                   &buf[..]);
    }

    impl AsOutputSegments for Vec<Vec<Word>> {
        fn as_output_segments<'a>(&'a self) -> OutputSegments<'a> {
            if self.len() == 0 {
                OutputSegments::SingleSegment([&[]])
            } else if self.len() == 1 {
                OutputSegments::SingleSegment([&self[0][..]])
            } else {
                OutputSegments::MultiSegment(self.iter()
                                             .map(|segment| &segment[..])
                                             .collect::<Vec<_>>())
            }
        }
    }

    /// Wraps a `Read` instance and introduces blocking.
    struct BlockingRead<R> where R: Read {
        /// The wrapped reader
        read: R,

        /// Number of bytes to read before blocking
        frequency: usize,

        /// Number of bytes read since last blocking
        idx: usize,
    }

    impl <R> BlockingRead<R> where R: Read {
        fn new(read: R, frequency: usize) -> BlockingRead<R> {
            BlockingRead { read: read, frequency: frequency, idx: 0 }
        }
    }

    impl <R> AsyncRead for BlockingRead<R> where R: Read + Unpin {
        fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context, buf: &mut [u8]) -> Poll<io::Result<usize>> {
            if self.idx == 0 {
                self.idx = self.frequency;
                cx.waker().clone().wake();
                Poll::Pending
            } else {
                let len = cmp::min(self.idx, buf.len());
                let bytes_read = match self.read.read(&mut buf[..len]) {
                    Err(e) => return Poll::Ready(Err(e)),
                    Ok(n) => n,
                };
                self.idx -= bytes_read;
                Poll::Ready(Ok(bytes_read))
            }
        }
    }

    /// Wraps a `Write` instance and introduces blocking.
    struct BlockingWrite<W> where W: Write {
        /// The wrapped writer
        writer: W,

        /// Number of bytes to write before blocking
        frequency: usize,

        /// Number of bytes written since last blocking
        idx: usize,
    }

    impl <W> BlockingWrite<W> where W: Write {
        fn new(writer: W, frequency: usize) -> BlockingWrite<W> {
            BlockingWrite { writer: writer, frequency: frequency, idx: 0 }
        }
        fn into_writer(self) -> W {
            self.writer
        }
    }

    impl <W> AsyncWrite for BlockingWrite<W> where W: Write + Unpin {
        fn poll_write(mut self: Pin<&mut Self>, cx: &mut Context, buf: &[u8]) -> Poll<io::Result<usize>> {
            if self.idx == 0 {
                self.idx = self.frequency;
                cx.waker().clone().wake();
                Poll::Pending
            } else {
                let len = cmp::min(self.idx, buf.len());
                let bytes_written = match self.writer.write(&buf[..len]) {
                    Err(e) => return Poll::Ready(Err(e)),
                    Ok(n) => n,
                };
                self.idx -= bytes_written;
                Poll::Ready(Ok(bytes_written))
            }
        }
        fn poll_flush(mut self: Pin<&mut Self>, _cx: &mut Context) -> Poll<io::Result<()>> {
            Poll::Ready(self.writer.flush())
        }

        fn poll_close(self: Pin<&mut Self>, _cx: &mut Context) -> Poll<io::Result<()>> {
            Poll::Ready(Ok(()))
        }
    }

    #[test]
    fn check_round_trip_async() {
        fn round_trip(read_block_frequency: usize,
                      write_block_frequency: usize,
                      segments: Vec<Vec<Word>>) -> TestResult
        {
            if segments.len() == 0 || read_block_frequency == 0 || write_block_frequency == 0 {
                return TestResult::discard();
            }

            let (mut read, segments) = {
                let cursor = std::io::Cursor::new(Vec::new());
                let mut writer = BlockingWrite::new(cursor, write_block_frequency);
                futures::executor::block_on(Box::pin(write_message(&mut writer, &segments))).expect("writing");

                let mut cursor = writer.into_writer();
                cursor.set_position(0);
                (BlockingRead::new(cursor, read_block_frequency), segments)
            };

            let message =
                futures::executor::block_on(Box::pin(read_message(&mut read, Default::default()))).expect("reading").unwrap();
            let message_segments = message.into_segments();

            TestResult::from_bool(segments.iter().enumerate().all(|(i, segment)| {
                &segment[..] == message_segments.get_segment(i as u32).unwrap()
            }))
        }

        quickcheck(round_trip as fn(usize, usize, Vec<Vec<Word>>) -> TestResult);
    }
}