mod lines;
mod read_line;
mod read_until;

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

cfg_if! {
    if #[cfg(feature = "docs")] {
        use std::ops::{Deref, DerefMut};

        #[doc(hidden)]
        pub struct ImplFuture<'a, T>(std::marker::PhantomData<&'a T>);

        /// Allows reading from a buffered byte stream.
        ///
        /// This trait is a re-export of [`futures::io::AsyncBufRead`] and is an async version of
        /// [`std::io::BufRead`].
        ///
        /// The [provided methods] do not really exist in the trait itself, but they become
        /// available when the prelude is imported:
        ///
        /// ```
        /// # #[allow(unused_imports)]
        /// use async_std::prelude::*;
        /// ```
        ///
        /// [`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
        /// [provided methods]: #provided-methods
        pub trait BufRead {
            /// 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 poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>;

            /// 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(self: Pin<&mut Self>, amt: usize);

            /// 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>,
            ) -> ImplFuture<'a, io::Result<usize>>
            where
                Self: Unpin,
            {
                unreachable!()
            }

            /// 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,
            ) -> ImplFuture<'a, io::Result<usize>>
            where
                Self: Unpin,
            {
                unreachable!()
            }

            /// 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,
            {
                unreachable!()
            }
        }

        impl<T: BufRead + Unpin + ?Sized> BufRead for Box<T> {
            fn poll_fill_buf(
                self: Pin<&mut Self>,
                cx: &mut Context<'_>,
            ) -> Poll<io::Result<&[u8]>> {
                unreachable!()
            }

            fn consume(self: Pin<&mut Self>, amt: usize) {
                unreachable!()
            }
        }

        impl<T: BufRead + Unpin + ?Sized> BufRead for &mut T {
            fn poll_fill_buf(
                self: Pin<&mut Self>,
                cx: &mut Context<'_>,
            ) -> Poll<io::Result<&[u8]>> {
                unreachable!()
            }

            fn consume(self: Pin<&mut Self>, amt: usize) {
                unreachable!()
            }
        }

        impl<P> BufRead for Pin<P>
        where
            P: DerefMut + Unpin,
            <P as Deref>::Target: BufRead,
        {
            fn poll_fill_buf(
                self: Pin<&mut Self>,
                cx: &mut Context<'_>,
            ) -> Poll<io::Result<&[u8]>> {
                unreachable!()
            }

            fn consume(self: Pin<&mut Self>, amt: usize) {
                unreachable!()
            }
        }

        impl BufRead for &[u8] {
            fn poll_fill_buf(
                self: Pin<&mut Self>,
                cx: &mut Context<'_>,
            ) -> Poll<io::Result<&[u8]>> {
                unreachable!()
            }

            fn consume(self: Pin<&mut Self>, amt: usize) {
                unreachable!()
            }
        }
    } else {
        pub use futures_io::AsyncBufRead as BufRead;
    }
}

#[doc(hidden)]
pub trait BufReadExt: futures_io::AsyncBufRead {
    fn read_until<'a>(&'a mut self, byte: u8, buf: &'a mut Vec<u8>) -> ReadUntilFuture<'a, Self>
    where
        Self: Unpin,
    {
        ReadUntilFuture {
            reader: self,
            byte,
            buf,
            read: 0,
        }
    }

    fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLineFuture<'a, Self>
    where
        Self: Unpin,
    {
        ReadLineFuture {
            reader: self,
            bytes: unsafe { mem::replace(buf.as_mut_vec(), Vec::new()) },
            buf,
            read: 0,
        }
    }

    fn lines(self) -> Lines<Self>
    where
        Self: Unpin + Sized,
    {
        Lines {
            reader: self,
            buf: String::new(),
            bytes: Vec::new(),
            read: 0,
        }
    }
}

impl<T: futures_io::AsyncBufRead + ?Sized> BufReadExt for T {}

pub fn read_until_internal<R: BufReadExt + ?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)));
        }
    }
}