//! Buffering wrappers for I/O traits

use alloc::boxed::Box;
use alloc::vec::Vec;
use core::cmp;
use core::fmt;

use crate::error;
use crate::file_io::memchr;
use crate::io::prelude::*;
use crate::io::{
	self, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, SeekFrom, DEFAULT_BUF_SIZE,
};

/// The `BufReader` struct adds buffering to any reader.
///
/// It can be excessively inefficient to work directly with a [`Read`] instance.
/// For example, every call to [`read`][`TcpStream::read`] on [`TcpStream`]
/// results in a system call. A `BufReader` performs large, infrequent reads on
/// the underlying [`Read`] and maintains an in-memory buffer of the results.
///
/// `BufReader` can improve the speed of programs that make *small* and
/// *repeated* read calls to the same file or network socket. It does not
/// help when reading very large amounts at once, or reading just one or a few
/// times. It also provides no advantage when reading from a source that is
/// already in memory, like a `Vec<u8>`.
///
/// When the `BufReader` is dropped, the contents of its buffer will be
/// discarded. Creating multiple instances of a `BufReader` on the same
/// stream can cause data loss.
///
/// [`Read`]: ../../std/io/trait.Read.html
/// [`TcpStream::read`]: ../../std/net/struct.TcpStream.html#method.read
/// [`TcpStream`]: ../../std/net/struct.TcpStream.html
///
/// # Examples
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::io::BufReader;
/// use std::fs::File;
///
/// fn main() -> std::io::Result<()> {
///     let f = File::open("log.txt")?;
///     let mut reader = BufReader::new(f);
///
///     let mut line = String::new();
///     let len = reader.read_line(&mut line)?;
///     println!("First line is {} bytes long", len);
///     Ok(())
/// }
/// ```
pub struct BufReader<R> {
	inner: R,
	buf: Box<[u8]>,
	pos: usize,
	cap: usize,
}

impl<R: Read> BufReader<R> {
	/// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
	/// but may change in the future.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufReader;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f = File::open("log.txt")?;
	///     let reader = BufReader::new(f);
	///     Ok(())
	/// }
	/// ```
	pub fn new(inner: R) -> BufReader<R> {
		BufReader::with_capacity(DEFAULT_BUF_SIZE, inner)
	}

	/// Creates a new `BufReader` with the specified buffer capacity.
	///
	/// # Examples
	///
	/// Creating a buffer with ten bytes of capacity:
	///
	/// ```no_run
	/// use std::io::BufReader;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f = File::open("log.txt")?;
	///     let reader = BufReader::with_capacity(10, f);
	///     Ok(())
	/// }
	/// ```
	pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
		unsafe {
			let mut buffer = Vec::with_capacity(capacity);
			buffer.set_len(capacity);
			inner.initializer().initialize(&mut buffer);
			BufReader {
				inner,
				buf: buffer.into_boxed_slice(),
				pos: 0,
				cap: 0,
			}
		}
	}
}

impl<R> BufReader<R> {
	/// Gets a reference to the underlying reader.
	///
	/// It is inadvisable to directly read from the underlying reader.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufReader;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f1 = File::open("log.txt")?;
	///     let reader = BufReader::new(f1);
	///
	///     let f2 = reader.get_ref();
	///     Ok(())
	/// }
	/// ```
	pub fn get_ref(&self) -> &R {
		&self.inner
	}

	/// Gets a mutable reference to the underlying reader.
	///
	/// It is inadvisable to directly read from the underlying reader.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufReader;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f1 = File::open("log.txt")?;
	///     let mut reader = BufReader::new(f1);
	///
	///     let f2 = reader.get_mut();
	///     Ok(())
	/// }
	/// ```
	pub fn get_mut(&mut self) -> &mut R {
		&mut self.inner
	}

	/// Returns a reference to the internally buffered data.
	///
	/// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
	///
	/// # Examples
	///
	/// ```no_run
	/// # #![feature(bufreader_buffer)]
	/// use std::io::{BufReader, BufRead};
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f = File::open("log.txt")?;
	///     let mut reader = BufReader::new(f);
	///     assert!(reader.buffer().is_empty());
	///
	///     if reader.fill_buf()?.len() > 0 {
	///         assert!(!reader.buffer().is_empty());
	///     }
	///     Ok(())
	/// }
	/// ```
	pub fn buffer(&self) -> &[u8] {
		&self.buf[self.pos..self.cap]
	}

	/// Unwraps this `BufReader`, returning the underlying reader.
	///
	/// Note that any leftover data in the internal buffer is lost.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufReader;
	/// use std::fs::File;
	///
	/// fn main() -> std::io::Result<()> {
	///     let f1 = File::open("log.txt")?;
	///     let reader = BufReader::new(f1);
	///
	///     let f2 = reader.into_inner();
	///     Ok(())
	/// }
	/// ```
	pub fn into_inner(self) -> R {
		self.inner
	}

	/// Invalidates all data in the internal buffer.
	#[inline]
	fn discard_buffer(&mut self) {
		self.pos = 0;
		self.cap = 0;
	}
}

impl<R: Seek> BufReader<R> {
	/// Seeks relative to the current position. If the new position lies within the buffer,
	/// the buffer will not be flushed, allowing for more efficient seeks.
	/// This method does not return the location of the underlying reader, so the caller
	/// must track this information themselves if it is required.
	pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
		let pos = self.pos as u64;
		if offset < 0 {
			if let Some(new_pos) = pos.checked_sub((-offset) as u64) {
				self.pos = new_pos as usize;
				return Ok(());
			}
		} else if let Some(new_pos) = pos.checked_add(offset as u64) {
			if new_pos <= self.cap as u64 {
				self.pos = new_pos as usize;
				return Ok(());
			}
		}
		self.seek(SeekFrom::Current(offset)).map(|_| ())
	}
}

impl<R: Read> Read for BufReader<R> {
	fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
		// If we don't have any buffered data and we're doing a massive read
		// (larger than our internal buffer), bypass our internal buffer
		// entirely.
		if self.pos == self.cap && buf.len() >= self.buf.len() {
			self.discard_buffer();
			return self.inner.read(buf);
		}
		let nread = {
			let mut rem = self.fill_buf()?;
			rem.read(buf)?
		};
		self.consume(nread);
		Ok(nread)
	}

	fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
		let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
		if self.pos == self.cap && total_len >= self.buf.len() {
			self.discard_buffer();
			return self.inner.read_vectored(bufs);
		}
		let nread = {
			let mut rem = self.fill_buf()?;
			rem.read_vectored(bufs)?
		};
		self.consume(nread);
		Ok(nread)
	}

	// we can't skip unconditionally because of the large buffer case in read.
	unsafe fn initializer(&self) -> Initializer {
		self.inner.initializer()
	}
}

impl<R: Read> BufRead for BufReader<R> {
	fn fill_buf(&mut self) -> io::Result<&[u8]> {
		// If we've reached the end of our internal buffer then we need to fetch
		// some more data from the underlying reader.
		// Branch using `>=` instead of the more correct `==`
		// to tell the compiler that the pos..cap slice is always valid.
		if self.pos >= self.cap {
			debug_assert!(self.pos == self.cap);
			self.cap = self.inner.read(&mut self.buf)?;
			self.pos = 0;
		}
		Ok(&self.buf[self.pos..self.cap])
	}

	fn consume(&mut self, amt: usize) {
		self.pos = cmp::min(self.pos + amt, self.cap);
	}
}

impl<R> fmt::Debug for BufReader<R>
where
	R: fmt::Debug,
{
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
		fmt.debug_struct("BufReader")
			.field("reader", &self.inner)
			.field(
				"buffer",
				&format_args!("{}/{}", self.cap - self.pos, self.buf.len()),
			)
			.finish()
	}
}

impl<R: Seek> Seek for BufReader<R> {
	/// Seek to an offset, in bytes, in the underlying reader.
	///
	/// The position used for seeking with `SeekFrom::Current(_)` is the
	/// position the underlying reader would be at if the `BufReader` had no
	/// internal buffer.
	///
	/// Seeking always discards the internal buffer, even if the seek position
	/// would otherwise fall within it. This guarantees that calling
	/// `.into_inner()` immediately after a seek yields the underlying reader
	/// at the same position.
	///
	/// To seek without discarding the internal buffer, use [`BufReader::seek_relative`].
	///
	/// See [`std::io::Seek`] for more details.
	///
	/// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
	/// where `n` minus the internal buffer length overflows an `i64`, two
	/// seeks will be performed instead of one. If the second seek returns
	/// `Err`, the underlying reader will be left at the same position it would
	/// have if you called `seek` with `SeekFrom::Current(0)`.
	///
	/// [`BufReader::seek_relative`]: struct.BufReader.html#method.seek_relative
	/// [`std::io::Seek`]: trait.Seek.html
	fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
		let result: u64;
		if let SeekFrom::Current(n) = pos {
			let remainder = (self.cap - self.pos) as i64;
			// it should be safe to assume that remainder fits within an i64 as the alternative
			// means we managed to allocate 8 exbibytes and that's absurd.
			// But it's not out of the realm of possibility for some weird underlying reader to
			// support seeking by i64::min_value() so we need to handle underflow when subtracting
			// remainder.
			if let Some(offset) = n.checked_sub(remainder) {
				result = self.inner.seek(SeekFrom::Current(offset))?;
			} else {
				// seek backwards by our remainder, and then by the offset
				self.inner.seek(SeekFrom::Current(-remainder))?;
				self.discard_buffer();
				result = self.inner.seek(SeekFrom::Current(n))?;
			}
		} else {
			// Seeking with Start/End doesn't care about our buffer length.
			result = self.inner.seek(pos)?;
		}
		self.discard_buffer();
		Ok(result)
	}
}

/// Wraps a writer and buffers its output.
///
/// It can be excessively inefficient to work directly with something that
/// implements [`Write`]. For example, every call to
/// [`write`][`TcpStream::write`] on [`TcpStream`] results in a system call. A
/// `BufWriter` keeps an in-memory buffer of data and writes it to an underlying
/// writer in large, infrequent batches.
///
/// `BufWriter` can improve the speed of programs that make *small* and
/// *repeated* write calls to the same file or network socket. It does not
/// help when writing very large amounts at once, or writing just one or a few
/// times. It also provides no advantage when writing to a destination that is
/// in memory, like a `Vec<u8>`.
///
/// When the `BufWriter` is dropped, the contents of its buffer will be written
/// out. However, any errors that happen in the process of flushing the buffer
/// when the writer is dropped will be ignored. Code that wishes to handle such
/// errors must manually call [`flush`] before the writer is dropped.
///
/// # Examples
///
/// Let's write the numbers one through ten to a [`TcpStream`]:
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::net::TcpStream;
///
/// let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap();
///
/// for i in 0..10 {
///     stream.write(&[i+1]).unwrap();
/// }
/// ```
///
/// Because we're not buffering, we write each one in turn, incurring the
/// overhead of a system call per byte written. We can fix this with a
/// `BufWriter`:
///
/// ```no_run
/// use std::io::prelude::*;
/// use std::io::BufWriter;
/// use std::net::TcpStream;
///
/// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
///
/// for i in 0..10 {
///     stream.write(&[i+1]).unwrap();
/// }
/// ```
///
/// By wrapping the stream with a `BufWriter`, these ten writes are all grouped
/// together by the buffer, and will all be written out in one system call when
/// the `stream` is dropped.
///
/// [`Write`]: ../../std/io/trait.Write.html
/// [`TcpStream::write`]: ../../std/net/struct.TcpStream.html#method.write
/// [`TcpStream`]: ../../std/net/struct.TcpStream.html
/// [`flush`]: #method.flush
pub struct BufWriter<W: Write> {
	inner: Option<W>,
	buf: Vec<u8>,
	// #30888: If the inner writer panics in a call to write, we don't want to
	// write the buffered data a second time in BufWriter's destructor. This
	// flag tells the Drop impl if it should skip the flush.
	panicked: bool,
}

/// An error returned by `into_inner` which combines an error that
/// happened while writing out the buffer, and the buffered writer object
/// which may be used to recover from the condition.
///
/// # Examples
///
/// ```no_run
/// use std::io::BufWriter;
/// use std::net::TcpStream;
///
/// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
///
/// // do stuff with the stream
///
/// // we want to get our `TcpStream` back, so let's try:
///
/// let stream = match stream.into_inner() {
///     Ok(s) => s,
///     Err(e) => {
///         // Here, e is an IntoInnerError
///         panic!("An error occurred");
///     }
/// };
/// ```
#[derive(Debug)]
pub struct IntoInnerError<W>(W, Error);

impl<W: Write> BufWriter<W> {
	/// Creates a new `BufWriter` with a default buffer capacity. The default is currently 8 KB,
	/// but may change in the future.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	/// ```
	pub fn new(inner: W) -> BufWriter<W> {
		BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
	}

	/// Creates a new `BufWriter` with the specified buffer capacity.
	///
	/// # Examples
	///
	/// Creating a buffer with a buffer of a hundred bytes.
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
	/// let mut buffer = BufWriter::with_capacity(100, stream);
	/// ```
	pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
		BufWriter {
			inner: Some(inner),
			buf: Vec::with_capacity(capacity),
			panicked: false,
		}
	}

	fn flush_buf(&mut self) -> io::Result<()> {
		let mut written = 0;
		let len = self.buf.len();
		let mut ret = Ok(());
		while written < len {
			self.panicked = true;
			let r = self.inner.as_mut().unwrap().write(&self.buf[written..]);
			self.panicked = false;

			match r {
				Ok(0) => {
					ret = Err(Error::new(
						ErrorKind::WriteZero,
						"failed to write the buffered data",
					));
					break;
				}
				Ok(n) => written += n,
				Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
				Err(e) => {
					ret = Err(e);
					break;
				}
			}
		}
		if written > 0 {
			self.buf.drain(..written);
		}
		ret
	}

	/// Gets a reference to the underlying writer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // we can use reference just like buffer
	/// let reference = buffer.get_ref();
	/// ```
	pub fn get_ref(&self) -> &W {
		self.inner.as_ref().unwrap()
	}

	/// Gets a mutable reference to the underlying writer.
	///
	/// It is inadvisable to directly write to the underlying writer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // we can use reference just like buffer
	/// let reference = buffer.get_mut();
	/// ```
	pub fn get_mut(&mut self) -> &mut W {
		self.inner.as_mut().unwrap()
	}

	/// Returns a reference to the internally buffered data.
	///
	/// # Examples
	///
	/// ```no_run
	/// # #![feature(bufreader_buffer)]
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // See how many bytes are currently buffered
	/// let bytes_buffered = buf_writer.buffer().len();
	/// ```
	pub fn buffer(&self) -> &[u8] {
		&self.buf
	}

	/// Unwraps this `BufWriter`, returning the underlying writer.
	///
	/// The buffer is written out before returning the writer.
	///
	/// # Errors
	///
	/// An `Err` will be returned if an error occurs while flushing the buffer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // unwrap the TcpStream and flush the buffer
	/// let stream = buffer.into_inner().unwrap();
	/// ```
	pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> {
		match self.flush_buf() {
			Err(e) => Err(IntoInnerError(self, e)),
			Ok(()) => Ok(self.inner.take().unwrap()),
		}
	}
}

impl<W: Write> Write for BufWriter<W> {
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
		if self.buf.len() + buf.len() > self.buf.capacity() {
			self.flush_buf()?;
		}
		if buf.len() >= self.buf.capacity() {
			self.panicked = true;
			let r = self.get_mut().write(buf);
			self.panicked = false;
			r
		} else {
			self.buf.write(buf)
		}
	}

	fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
		let total_len = bufs.iter().map(|b| b.len()).sum::<usize>();
		if self.buf.len() + total_len > self.buf.capacity() {
			self.flush_buf()?;
		}
		if total_len >= self.buf.capacity() {
			self.panicked = true;
			let r = self.get_mut().write_vectored(bufs);
			self.panicked = false;
			r
		} else {
			self.buf.write_vectored(bufs)
		}
	}

	fn flush(&mut self) -> io::Result<()> {
		self.flush_buf().and_then(|()| self.get_mut().flush())
	}
}

impl<W: Write> fmt::Debug for BufWriter<W>
where
	W: fmt::Debug,
{
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
		fmt.debug_struct("BufWriter")
			.field("writer", &self.inner.as_ref().unwrap())
			.field(
				"buffer",
				&format_args!("{}/{}", self.buf.len(), self.buf.capacity()),
			)
			.finish()
	}
}

impl<W: Write + Seek> Seek for BufWriter<W> {
	/// Seek to the offset, in bytes, in the underlying writer.
	///
	/// Seeking always writes out the internal buffer before seeking.
	fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
		self.flush_buf().and_then(|_| self.get_mut().seek(pos))
	}
}

impl<W: Write> Drop for BufWriter<W> {
	fn drop(&mut self) {
		if self.inner.is_some() && !self.panicked {
			// dtors should not panic, so we ignore a failed flush
			let _r = self.flush_buf();
		}
	}
}

impl<W> IntoInnerError<W> {
	/// Returns the error which caused the call to `into_inner()` to fail.
	///
	/// This error was returned when attempting to write the internal buffer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // do stuff with the stream
	///
	/// // we want to get our `TcpStream` back, so let's try:
	///
	/// let stream = match stream.into_inner() {
	///     Ok(s) => s,
	///     Err(e) => {
	///         // Here, e is an IntoInnerError, let's log the inner error.
	///         //
	///         // We'll just 'log' to stdout for this example.
	///         println!("{}", e.error());
	///
	///         panic!("An unexpected error occurred.");
	///     }
	/// };
	/// ```
	pub fn error(&self) -> &Error {
		&self.1
	}

	/// Returns the buffered writer instance which generated the error.
	///
	/// The returned object can be used for error recovery, such as
	/// re-inspecting the buffer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::io::BufWriter;
	/// use std::net::TcpStream;
	///
	/// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());
	///
	/// // do stuff with the stream
	///
	/// // we want to get our `TcpStream` back, so let's try:
	///
	/// let stream = match stream.into_inner() {
	///     Ok(s) => s,
	///     Err(e) => {
	///         // Here, e is an IntoInnerError, let's re-examine the buffer:
	///         let buffer = e.into_inner();
	///
	///         // do stuff to try to recover
	///
	///         // afterwards, let's just return the stream
	///         buffer.into_inner().unwrap()
	///     }
	/// };
	/// ```
	pub fn into_inner(self) -> W {
		self.0
	}
}

impl<W> From<IntoInnerError<W>> for Error {
	fn from(iie: IntoInnerError<W>) -> Error {
		iie.1
	}
}

impl<W: Send + fmt::Debug> error::Error for IntoInnerError<W> {
	fn description(&self) -> &str {
		error::Error::description(self.error())
	}
}

impl<W> fmt::Display for IntoInnerError<W> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		self.error().fmt(f)
	}
}

/// Wraps a writer and buffers output to it, flushing whenever a newline
/// (`0x0a`, `'\n'`) is detected.
///
/// The [`BufWriter`][bufwriter] struct wraps a writer and buffers its output.
/// But it only does this batched write when it goes out of scope, or when the
/// internal buffer is full. Sometimes, you'd prefer to write each line as it's
/// completed, rather than the entire buffer at once. Enter `LineWriter`. It
/// does exactly that.
///
/// Like [`BufWriter`], a `LineWriter`’s buffer will also be flushed when the
/// `LineWriter` goes out of scope or when its internal buffer is full.
///
/// [bufwriter]: struct.BufWriter.html
///
/// If there's still a partial line in the buffer when the `LineWriter` is
/// dropped, it will flush those contents.
///
/// # Examples
///
/// We can use `LineWriter` to write one line at a time, significantly
/// reducing the number of actual writes to the file.
///
/// ```no_run
/// use std::fs::{self, File};
/// use std::io::prelude::*;
/// use std::io::LineWriter;
///
/// fn main() -> std::io::Result<()> {
///     let road_not_taken = b"I shall be telling this with a sigh
/// Somewhere ages and ages hence:
/// Two roads diverged in a wood, and I -
/// I took the one less traveled by,
/// And that has made all the difference.";
///
///     let file = File::create("poem.txt")?;
///     let mut file = LineWriter::new(file);
///
///     file.write_all(b"I shall be telling this with a sigh")?;
///
///     // No bytes are written until a newline is encountered (or
///     // the internal buffer is filled).
///     assert_eq!(fs::read_to_string("poem.txt")?, "");
///     file.write_all(b"\n")?;
///     assert_eq!(
///         fs::read_to_string("poem.txt")?,
///         "I shall be telling this with a sigh\n",
///     );
///
///     // Write the rest of the poem.
///     file.write_all(b"Somewhere ages and ages hence:
/// Two roads diverged in a wood, and I -
/// I took the one less traveled by,
/// And that has made all the difference.")?;
///
///     // The last line of the poem doesn't end in a newline, so
///     // we have to flush or drop the `LineWriter` to finish
///     // writing.
///     file.flush()?;
///
///     // Confirm the whole poem was written.
///     assert_eq!(fs::read("poem.txt")?, &road_not_taken[..]);
///     Ok(())
/// }
/// ```
pub struct LineWriter<W: Write> {
	inner: BufWriter<W>,
	need_flush: bool,
}

impl<W: Write> LineWriter<W> {
	/// Creates a new `LineWriter`.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::fs::File;
	/// use std::io::LineWriter;
	///
	/// fn main() -> std::io::Result<()> {
	///     let file = File::create("poem.txt")?;
	///     let file = LineWriter::new(file);
	///     Ok(())
	/// }
	/// ```
	pub fn new(inner: W) -> LineWriter<W> {
		// Lines typically aren't that long, don't use a giant buffer
		LineWriter::with_capacity(1024, inner)
	}

	/// Creates a new `LineWriter` with a specified capacity for the internal
	/// buffer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::fs::File;
	/// use std::io::LineWriter;
	///
	/// fn main() -> std::io::Result<()> {
	///     let file = File::create("poem.txt")?;
	///     let file = LineWriter::with_capacity(100, file);
	///     Ok(())
	/// }
	/// ```
	pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
		LineWriter {
			inner: BufWriter::with_capacity(capacity, inner),
			need_flush: false,
		}
	}

	/// Gets a reference to the underlying writer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::fs::File;
	/// use std::io::LineWriter;
	///
	/// fn main() -> std::io::Result<()> {
	///     let file = File::create("poem.txt")?;
	///     let file = LineWriter::new(file);
	///
	///     let reference = file.get_ref();
	///     Ok(())
	/// }
	/// ```
	pub fn get_ref(&self) -> &W {
		self.inner.get_ref()
	}

	/// Gets a mutable reference to the underlying writer.
	///
	/// Caution must be taken when calling methods on the mutable reference
	/// returned as extra writes could corrupt the output stream.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::fs::File;
	/// use std::io::LineWriter;
	///
	/// fn main() -> std::io::Result<()> {
	///     let file = File::create("poem.txt")?;
	///     let mut file = LineWriter::new(file);
	///
	///     // we can use reference just like file
	///     let reference = file.get_mut();
	///     Ok(())
	/// }
	/// ```
	pub fn get_mut(&mut self) -> &mut W {
		self.inner.get_mut()
	}

	/// Unwraps this `LineWriter`, returning the underlying writer.
	///
	/// The internal buffer is written out before returning the writer.
	///
	/// # Errors
	///
	/// An `Err` will be returned if an error occurs while flushing the buffer.
	///
	/// # Examples
	///
	/// ```no_run
	/// use std::fs::File;
	/// use std::io::LineWriter;
	///
	/// fn main() -> std::io::Result<()> {
	///     let file = File::create("poem.txt")?;
	///
	///     let writer: LineWriter<File> = LineWriter::new(file);
	///
	///     let file: File = writer.into_inner()?;
	///     Ok(())
	/// }
	/// ```
	pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> {
		self.inner.into_inner().map_err(|IntoInnerError(buf, e)| {
			IntoInnerError(
				LineWriter {
					inner: buf,
					need_flush: false,
				},
				e,
			)
		})
	}
}

impl<W: Write> Write for LineWriter<W> {
	fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
		if self.need_flush {
			self.flush()?;
		}

		// Find the last newline character in the buffer provided. If found then
		// we're going to write all the data up to that point and then flush,
		// otherwise we just write the whole block to the underlying writer.
		let i = match memchr::memrchr(b'\n', buf) {
			Some(i) => i,
			None => return self.inner.write(buf),
		};

		// Ok, we're going to write a partial amount of the data given first
		// followed by flushing the newline. After we've successfully written
		// some data then we *must* report that we wrote that data, so future
		// errors are ignored. We set our internal `need_flush` flag, though, in
		// case flushing fails and we need to try it first next time.
		let n = self.inner.write(&buf[..=i])?;
		self.need_flush = true;
		if self.flush().is_err() || n != i + 1 {
			return Ok(n);
		}

		// At this point we successfully wrote `i + 1` bytes and flushed it out,
		// meaning that the entire line is now flushed out on the screen. While
		// we can attempt to finish writing the rest of the data provided.
		// Remember though that we ignore errors here as we've successfully
		// written data, so we need to report that.
		match self.inner.write(&buf[i + 1..]) {
			Ok(i) => Ok(n + i),
			Err(_) => Ok(n),
		}
	}

	fn flush(&mut self) -> io::Result<()> {
		self.inner.flush()?;
		self.need_flush = false;
		Ok(())
	}
}

impl<W: Write> fmt::Debug for LineWriter<W>
where
	W: fmt::Debug,
{
	fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
		fmt.debug_struct("LineWriter")
			.field("writer", &self.inner.inner)
			.field(
				"buffer",
				&format_args!("{}/{}", self.inner.buf.len(), self.inner.buf.capacity()),
			)
			.finish()
	}
}

#[cfg(test)]
mod tests {
	use alloc::string::{String, ToString};
	use alloc::vec;
	use alloc::vec::Vec;

	use crate::io::prelude::*;
	use crate::io::{self, BufReader, BufWriter, LineWriter, SeekFrom};

	/// A dummy reader intended at testing short-reads propagation.
	pub struct ShortReader {
		lengths: Vec<usize>,
	}

	impl Read for ShortReader {
		fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
			if self.lengths.is_empty() {
				Ok(0)
			} else {
				Ok(self.lengths.remove(0))
			}
		}
	}

	#[test]
	fn test_buffered_reader() {
		let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
		let mut reader = BufReader::with_capacity(2, inner);

		let mut buf = [0, 0, 0];
		let nread = reader.read(&mut buf);
		assert_eq!(nread.unwrap(), 3);
		assert_eq!(buf, [5, 6, 7]);
		assert_eq!(reader.buffer(), []);

		let mut buf = [0, 0];
		let nread = reader.read(&mut buf);
		assert_eq!(nread.unwrap(), 2);
		assert_eq!(buf, [0, 1]);
		assert_eq!(reader.buffer(), []);

		let mut buf = [0];
		let nread = reader.read(&mut buf);
		assert_eq!(nread.unwrap(), 1);
		assert_eq!(buf, [2]);
		assert_eq!(reader.buffer(), [3]);

		let mut buf = [0, 0, 0];
		let nread = reader.read(&mut buf);
		assert_eq!(nread.unwrap(), 1);
		assert_eq!(buf, [3, 0, 0]);
		assert_eq!(reader.buffer(), []);

		let nread = reader.read(&mut buf);
		assert_eq!(nread.unwrap(), 1);
		assert_eq!(buf, [4, 0, 0]);
		assert_eq!(reader.buffer(), []);

		assert_eq!(reader.read(&mut buf).unwrap(), 0);
	}

	#[test]
	fn test_buffered_reader_seek() {
		let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
		let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));

		assert_eq!(reader.seek(SeekFrom::Start(3)).ok(), Some(3));
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
		assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(3));
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
		assert_eq!(reader.seek(SeekFrom::Current(1)).ok(), Some(4));
		assert_eq!(reader.fill_buf().ok(), Some(&[1, 2][..]));
		reader.consume(1);
		assert_eq!(reader.seek(SeekFrom::Current(-2)).ok(), Some(3));
	}

	#[test]
	fn test_buffered_reader_seek_relative() {
		let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
		let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner));

		assert!(reader.seek_relative(3).is_ok());
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
		assert!(reader.seek_relative(0).is_ok());
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
		assert!(reader.seek_relative(1).is_ok());
		assert_eq!(reader.fill_buf().ok(), Some(&[1][..]));
		assert!(reader.seek_relative(-1).is_ok());
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..]));
		assert!(reader.seek_relative(2).is_ok());
		assert_eq!(reader.fill_buf().ok(), Some(&[2, 3][..]));
	}

	#[test]
	fn test_buffered_reader_invalidated_after_read() {
		let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
		let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner));

		assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..]));
		reader.consume(3);

		let mut buffer = [0, 0, 0, 0, 0];
		assert_eq!(reader.read(&mut buffer).ok(), Some(5));
		assert_eq!(buffer, [0, 1, 2, 3, 4]);

		assert!(reader.seek_relative(-2).is_ok());
		let mut buffer = [0, 0];
		assert_eq!(reader.read(&mut buffer).ok(), Some(2));
		assert_eq!(buffer, [3, 4]);
	}

	#[test]
	fn test_buffered_reader_invalidated_after_seek() {
		let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4];
		let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner));

		assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..]));
		reader.consume(3);

		assert!(reader.seek(SeekFrom::Current(5)).is_ok());

		assert!(reader.seek_relative(-2).is_ok());
		let mut buffer = [0, 0];
		assert_eq!(reader.read(&mut buffer).ok(), Some(2));
		assert_eq!(buffer, [3, 4]);
	}

	#[test]
	fn test_buffered_reader_seek_underflow() {
		// gimmick reader that yields its position modulo 256 for each byte
		struct PositionReader {
			pos: u64,
		}
		impl Read for PositionReader {
			fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
				let len = buf.len();
				for x in buf {
					*x = self.pos as u8;
					self.pos = self.pos.wrapping_add(1);
				}
				Ok(len)
			}
		}
		impl Seek for PositionReader {
			fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
				match pos {
					SeekFrom::Start(n) => {
						self.pos = n;
					}
					SeekFrom::Current(n) => {
						self.pos = self.pos.wrapping_add(n as u64);
					}
					SeekFrom::End(n) => {
						self.pos = u64::max_value().wrapping_add(n as u64);
					}
				}
				Ok(self.pos)
			}
		}

		let mut reader = BufReader::with_capacity(5, PositionReader { pos: 0 });
		assert_eq!(reader.fill_buf().ok(), Some(&[0, 1, 2, 3, 4][..]));
		assert_eq!(
			reader.seek(SeekFrom::End(-5)).ok(),
			Some(u64::max_value() - 5)
		);
		assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
		// the following seek will require two underlying seeks
		let expected = 9_223_372_036_854_775_802;
		assert_eq!(
			reader.seek(SeekFrom::Current(i64::min_value())).ok(),
			Some(expected)
		);
		assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5));
		// seeking to 0 should empty the buffer.
		assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(expected));
		assert_eq!(reader.get_ref().pos, expected);
	}

	#[test]
	fn test_buffered_writer() {
		let inner = Vec::new();
		let mut writer = BufWriter::with_capacity(2, inner);

		writer.write(&[0, 1]).unwrap();
		assert_eq!(writer.buffer(), []);
		assert_eq!(*writer.get_ref(), [0, 1]);

		writer.write(&[2]).unwrap();
		assert_eq!(writer.buffer(), [2]);
		assert_eq!(*writer.get_ref(), [0, 1]);

		writer.write(&[3]).unwrap();
		assert_eq!(writer.buffer(), [2, 3]);
		assert_eq!(*writer.get_ref(), [0, 1]);

		writer.flush().unwrap();
		assert_eq!(writer.buffer(), []);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);

		writer.write(&[4]).unwrap();
		writer.write(&[5]).unwrap();
		assert_eq!(writer.buffer(), [4, 5]);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3]);

		writer.write(&[6]).unwrap();
		assert_eq!(writer.buffer(), [6]);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5]);

		writer.write(&[7, 8]).unwrap();
		assert_eq!(writer.buffer(), []);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8]);

		writer.write(&[9, 10, 11]).unwrap();
		assert_eq!(writer.buffer(), []);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);

		writer.flush().unwrap();
		assert_eq!(writer.buffer(), []);
		assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
	}

	#[test]
	fn test_buffered_writer_inner_flushes() {
		let mut w = BufWriter::with_capacity(3, Vec::new());
		w.write(&[0, 1]).unwrap();
		assert_eq!(*w.get_ref(), []);
		let w = w.into_inner().unwrap();
		assert_eq!(w, [0, 1]);
	}

	#[test]
	fn test_buffered_writer_seek() {
		let mut w = BufWriter::with_capacity(3, io::Cursor::new(Vec::new()));
		w.write_all(&[0, 1, 2, 3, 4, 5]).unwrap();
		w.write_all(&[6, 7]).unwrap();
		assert_eq!(w.seek(SeekFrom::Current(0)).ok(), Some(8));
		assert_eq!(&w.get_ref().get_ref()[..], &[0, 1, 2, 3, 4, 5, 6, 7][..]);
		assert_eq!(w.seek(SeekFrom::Start(2)).ok(), Some(2));
		w.write_all(&[8, 9]).unwrap();
		assert_eq!(
			&w.into_inner().unwrap().into_inner()[..],
			&[0, 1, 8, 9, 4, 5, 6, 7]
		);
	}

	#[test]
	fn test_read_until() {
		let inner: &[u8] = &[0, 1, 2, 1, 0];
		let mut reader = BufReader::with_capacity(2, inner);
		let mut v = Vec::new();
		reader.read_until(0, &mut v).unwrap();
		assert_eq!(v, [0]);
		v.truncate(0);
		reader.read_until(2, &mut v).unwrap();
		assert_eq!(v, [1, 2]);
		v.truncate(0);
		reader.read_until(1, &mut v).unwrap();
		assert_eq!(v, [1]);
		v.truncate(0);
		reader.read_until(8, &mut v).unwrap();
		assert_eq!(v, [0]);
		v.truncate(0);
		reader.read_until(9, &mut v).unwrap();
		assert_eq!(v, []);
	}

	#[test]
	fn test_line_buffer_fail_flush() {
		// Issue #32085
		struct FailFlushWriter<'a>(&'a mut Vec<u8>);

		impl Write for FailFlushWriter<'_> {
			fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
				self.0.extend_from_slice(buf);
				Ok(buf.len())
			}
			fn flush(&mut self) -> io::Result<()> {
				Err(io::Error::new(io::ErrorKind::Other, "flush failed"))
			}
		}

		let mut buf = Vec::new();
		{
			let mut writer = LineWriter::new(FailFlushWriter(&mut buf));
			let to_write = b"abc\ndef";
			if let Ok(written) = writer.write(to_write) {
				assert!(written < to_write.len(), "didn't flush on new line");
				// PASS
				return;
			}
		}
		assert!(buf.is_empty(), "write returned an error but wrote data");
	}

	#[test]
	fn test_line_buffer() {
		let mut writer = LineWriter::new(Vec::new());
		writer.write(&[0]).unwrap();
		assert_eq!(*writer.get_ref(), []);
		writer.write(&[1]).unwrap();
		assert_eq!(*writer.get_ref(), []);
		writer.flush().unwrap();
		assert_eq!(*writer.get_ref(), [0, 1]);
		writer.write(&[0, b'\n', 1, b'\n', 2]).unwrap();
		assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n']);
		writer.flush().unwrap();
		assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2]);
		writer.write(&[3, b'\n']).unwrap();
		assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2, 3, b'\n']);
	}

	#[test]
	fn test_read_line() {
		let in_buf: &[u8] = b"a\nb\nc";
		let mut reader = BufReader::with_capacity(2, in_buf);
		let mut s = String::new();
		reader.read_line(&mut s).unwrap();
		assert_eq!(s, "a\n");
		s.truncate(0);
		reader.read_line(&mut s).unwrap();
		assert_eq!(s, "b\n");
		s.truncate(0);
		reader.read_line(&mut s).unwrap();
		assert_eq!(s, "c");
		s.truncate(0);
		reader.read_line(&mut s).unwrap();
		assert_eq!(s, "");
	}

	#[test]
	fn test_lines() {
		let in_buf: &[u8] = b"a\nb\nc";
		let reader = BufReader::with_capacity(2, in_buf);
		let mut it = reader.lines();
		assert_eq!(it.next().unwrap().unwrap(), "a".to_string());
		assert_eq!(it.next().unwrap().unwrap(), "b".to_string());
		assert_eq!(it.next().unwrap().unwrap(), "c".to_string());
		assert!(it.next().is_none());
	}

	#[test]
	fn test_short_reads() {
		let inner = ShortReader {
			lengths: vec![0, 1, 2, 0, 1, 0],
		};
		let mut reader = BufReader::new(inner);
		let mut buf = [0, 0];
		assert_eq!(reader.read(&mut buf).unwrap(), 0);
		assert_eq!(reader.read(&mut buf).unwrap(), 1);
		assert_eq!(reader.read(&mut buf).unwrap(), 2);
		assert_eq!(reader.read(&mut buf).unwrap(), 0);
		assert_eq!(reader.read(&mut buf).unwrap(), 1);
		assert_eq!(reader.read(&mut buf).unwrap(), 0);
		assert_eq!(reader.read(&mut buf).unwrap(), 0);
	}

	#[test]
	#[should_panic]
	fn dont_panic_in_drop_on_panicked_flush() {
		struct FailFlushWriter;

		impl Write for FailFlushWriter {
			fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
				Ok(buf.len())
			}
			fn flush(&mut self) -> io::Result<()> {
				Err(io::Error::last_os_error())
			}
		}

		let writer = FailFlushWriter;
		let _writer = BufWriter::new(writer);

		// If writer panics *again* due to the flush error then the process will
		// abort.
		panic!();
	}

	struct AcceptOneThenFail {
		written: bool,
		flushed: bool,
	}

	impl Write for AcceptOneThenFail {
		fn write(&mut self, data: &[u8]) -> io::Result<usize> {
			if !self.written {
				assert_eq!(data, b"a\nb\n");
				self.written = true;
				Ok(data.len())
			} else {
				Err(io::Error::new(io::ErrorKind::NotFound, "test"))
			}
		}

		fn flush(&mut self) -> io::Result<()> {
			assert!(self.written);
			assert!(!self.flushed);
			self.flushed = true;
			Err(io::Error::new(io::ErrorKind::Other, "test"))
		}
	}

	#[test]
	fn erroneous_flush_retried() {
		let a = AcceptOneThenFail {
			written: false,
			flushed: false,
		};

		let mut l = LineWriter::new(a);
		assert_eq!(l.write(b"a\nb\na").unwrap(), 4);
		assert!(l.get_ref().written);
		assert!(l.get_ref().flushed);
		l.get_mut().flushed = false;

		assert_eq!(l.write(b"a").unwrap_err().kind(), io::ErrorKind::Other)
	}
}