mod fill_buf;
mod lines;
mod read_line;
mod read_until;

use fill_buf::FillBufFuture;
pub use lines::Lines;
use read_line::ReadLineFuture;
use read_until::ReadUntilFuture;

use std::mem;
use std::pin::Pin;

use cfg_if::cfg_if;
use futures_io::AsyncBufRead;

use crate::io;
use crate::task::{Context, Poll};

cfg_if! {
    if #[cfg(feature = "docs")] {
        #[doc(hidden)]
        pub struct ImplFuture<'a, T>(std::marker::PhantomData<&'a T>);

        macro_rules! ret {
            ($a:lifetime, $f:tt, $o:ty) => (ImplFuture<$a, $o>);
        }
    } else {
        macro_rules! ret {
            ($a:lifetime, $f:tt, $o:ty) => ($f<$a, Self>);
        }
    }
}

/// Allows reading from a buffered byte stream.
///
/// This trait is an async version of [`std::io::BufRead`].
///
/// While it is currently not possible to implement this trait directly, it gets implemented
/// automatically for all types that implement [`futures::io::AsyncBufRead`].
///
/// [`std::io::BufRead`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
/// [`futures::io::AsyncBufRead`]:
/// https://docs.rs/futures-preview/0.3.0-alpha.17/futures/io/trait.AsyncBufRead.html
pub trait BufRead {
    /// Tells this buffer that `amt` bytes have been consumed from the buffer, so they should no
    /// longer be returned in calls to `read`.
    fn consume(&mut self, amt: usize)
    where
        Self: Unpin;

    /// Returns the contents of the internal buffer, filling it with more data from the inner
    /// reader if it is empty.
    ///
    /// This function is a lower-level call. It needs to be paired with the [`consume`] method to
    /// function properly. When calling this method, none of the contents will be "read" in the
    /// sense that later calling `read` may return the same contents. As such, [`consume`] must be
    /// called with the number of bytes that are consumed from this buffer to ensure that the bytes
    /// are never returned twice.
    ///
    /// [`consume`]: #tymethod.consume
    ///
    /// An empty buffer returned indicates that the stream has reached EOF.
    // TODO: write a proper doctest with `consume`
    fn fill_buf<'a>(&'a mut self) -> ret!('a, FillBufFuture, io::Result<&'a [u8]>)
    where
        Self: Unpin,
    {
        FillBufFuture::new(self)
    }

    /// Reads all bytes into `buf` until the delimiter `byte` or EOF is reached.
    ///
    /// This function will read bytes from the underlying stream until the delimiter or EOF is
    /// found. Once found, all bytes up to, and including, the delimiter (if found) will be
    /// appended to `buf`.
    ///
    /// If successful, this function will return the total number of bytes read.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
    /// #
    /// use async_std::fs::File;
    /// use async_std::io::BufReader;
    /// use async_std::prelude::*;
    ///
    /// let mut file = BufReader::new(File::open("a.txt").await?);
    ///
    /// let mut buf = Vec::with_capacity(1024);
    /// let n = file.read_until(b'\n', &mut buf).await?;
    /// #
    /// # Ok(()) }) }
    /// ```
    ///
    /// Multiple successful calls to `read_until` append all bytes up to and including to `buf`:
    /// ```
    /// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
    /// #
    /// use async_std::io::BufReader;
    /// use async_std::prelude::*;
    ///
    /// let from: &[u8] = b"append\nexample\n";
    /// let mut reader = BufReader::new(from);
    /// let mut buf = vec![];
    ///
    /// let mut size = reader.read_until(b'\n', &mut buf).await?;
    /// assert_eq!(size, 7);
    /// assert_eq!(buf, b"append\n");
    ///
    /// size += reader.read_until(b'\n', &mut buf).await?;
    /// assert_eq!(size, from.len());
    ///
    /// assert_eq!(buf, from);
    /// #
    /// # Ok(()) }) }
    /// ```
    fn read_until<'a>(
        &'a mut self,
        byte: u8,
        buf: &'a mut Vec<u8>,
    ) -> ret!('a, ReadUntilFuture, io::Result<usize>)
    where
        Self: Unpin,
    {
        ReadUntilFuture {
            reader: self,
            byte,
            buf,
            read: 0,
        }
    }

    /// Reads all bytes and appends them into `buf` until a newline (the 0xA byte) is reached.
    ///
    /// This function will read bytes from the underlying stream until the newline delimiter (the
    /// 0xA byte) or EOF is found. Once found, all bytes up to, and including, the delimiter (if
    /// found) will be appended to `buf`.
    ///
    /// If successful, this function will return the total number of bytes read.
    ///
    /// If this function returns `Ok(0)`, the stream has reached EOF.
    ///
    /// # Errors
    ///
    /// This function has the same error semantics as [`read_until`] and will also return an error
    /// if the read bytes are not valid UTF-8. If an I/O error is encountered then `buf` may
    /// contain some bytes already read in the event that all data read so far was valid UTF-8.
    ///
    /// [`read_until`]: #method.read_until
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
    /// #
    /// use async_std::fs::File;
    /// use async_std::io::BufReader;
    /// use async_std::prelude::*;
    ///
    /// let mut file = BufReader::new(File::open("a.txt").await?);
    ///
    /// let mut buf = String::new();
    /// file.read_line(&mut buf).await?;
    /// #
    /// # Ok(()) }) }
    /// ```
    fn read_line<'a>(
        &'a mut self,
        buf: &'a mut String,
    ) -> ret!('a, ReadLineFuture, io::Result<usize>)
    where
        Self: Unpin,
    {
        ReadLineFuture {
            reader: self,
            bytes: unsafe { mem::replace(buf.as_mut_vec(), Vec::new()) },
            buf,
            read: 0,
        }
    }

    /// Returns a stream over the lines of this byte stream.
    ///
    /// The stream returned from this function will yield instances of
    /// [`io::Result`]`<`[`String`]`>`. Each string returned will *not* have a newline byte (the
    /// 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
    ///
    /// [`io::Result`]: type.Result.html
    /// [`String`]: https://doc.rust-lang.org/std/string/struct.String.html
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # fn main() -> std::io::Result<()> { async_std::task::block_on(async {
    /// #
    /// use async_std::fs::File;
    /// use async_std::io::BufReader;
    /// use async_std::prelude::*;
    ///
    /// let file = File::open("a.txt").await?;
    /// let mut lines = BufReader::new(file).lines();
    /// let mut count = 0;
    ///
    /// while let Some(line) = lines.next().await {
    ///     line?;
    ///     count += 1;
    /// }
    /// #
    /// # Ok(()) }) }
    /// ```
    fn lines(self) -> Lines<Self>
    where
        Self: Unpin + Sized,
    {
        Lines {
            reader: self,
            buf: String::new(),
            bytes: Vec::new(),
            read: 0,
        }
    }
}

impl<T: AsyncBufRead + Unpin + ?Sized> BufRead for T {
    fn consume(&mut self, amt: usize) {
        AsyncBufRead::consume(Pin::new(self), amt)
    }
}

pub fn read_until_internal<R: AsyncBufRead + ?Sized>(
    mut reader: Pin<&mut R>,
    cx: &mut Context<'_>,
    byte: u8,
    buf: &mut Vec<u8>,
    read: &mut usize,
) -> Poll<io::Result<usize>> {
    loop {
        let (done, used) = {
            let available = futures_core::ready!(reader.as_mut().poll_fill_buf(cx))?;
            if let Some(i) = memchr::memchr(byte, available) {
                buf.extend_from_slice(&available[..=i]);
                (true, i + 1)
            } else {
                buf.extend_from_slice(available);
                (false, available.len())
            }
        };
        reader.as_mut().consume(used);
        *read += used;
        if done || used == 0 {
            return Poll::Ready(Ok(mem::replace(read, 0)));
        }
    }
}