#[cfg(test)]
mod tests;

use crate::alloc::Allocator;
use crate::cmp;
use crate::collections::VecDeque;
use crate::fmt;
use crate::io::{
    self, BorrowedCursor, BufRead, ErrorKind, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write,
};
use crate::mem;
use crate::str;

// =============================================================================
// 转发实现

#[stable(feature = "rust1", since = "1.0.0")]
impl<R: Read + ?Sized> Read for &mut R {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        (**self).read(buf)
    }

    #[inline]
    fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
        (**self).read_buf(cursor)
    }

    #[inline]
    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        (**self).read_vectored(bufs)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        (**self).is_read_vectored()
    }

    #[inline]
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        (**self).read_to_end(buf)
    }

    #[inline]
    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        (**self).read_to_string(buf)
    }

    #[inline]
    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        (**self).read_exact(buf)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<W: Write + ?Sized> Write for &mut W {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        (**self).write(buf)
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        (**self).write_vectored(bufs)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        (**self).is_write_vectored()
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        (**self).flush()
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        (**self).write_all(buf)
    }

    #[inline]
    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
        (**self).write_fmt(fmt)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<S: Seek + ?Sized> Seek for &mut S {
    #[inline]
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        (**self).seek(pos)
    }

    #[inline]
    fn stream_position(&mut self) -> io::Result<u64> {
        (**self).stream_position()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B: BufRead + ?Sized> BufRead for &mut B {
    #[inline]
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        (**self).fill_buf()
    }

    #[inline]
    fn consume(&mut self, amt: usize) {
        (**self).consume(amt)
    }

    #[inline]
    fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
        (**self).read_until(byte, buf)
    }

    #[inline]
    fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
        (**self).read_line(buf)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<R: Read + ?Sized> Read for Box<R> {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        (**self).read(buf)
    }

    #[inline]
    fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
        (**self).read_buf(cursor)
    }

    #[inline]
    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        (**self).read_vectored(bufs)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        (**self).is_read_vectored()
    }

    #[inline]
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        (**self).read_to_end(buf)
    }

    #[inline]
    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        (**self).read_to_string(buf)
    }

    #[inline]
    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        (**self).read_exact(buf)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<W: Write + ?Sized> Write for Box<W> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        (**self).write(buf)
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        (**self).write_vectored(bufs)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        (**self).is_write_vectored()
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        (**self).flush()
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        (**self).write_all(buf)
    }

    #[inline]
    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
        (**self).write_fmt(fmt)
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<S: Seek + ?Sized> Seek for Box<S> {
    #[inline]
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        (**self).seek(pos)
    }

    #[inline]
    fn stream_position(&mut self) -> io::Result<u64> {
        (**self).stream_position()
    }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<B: BufRead + ?Sized> BufRead for Box<B> {
    #[inline]
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        (**self).fill_buf()
    }

    #[inline]
    fn consume(&mut self, amt: usize) {
        (**self).consume(amt)
    }

    #[inline]
    fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize> {
        (**self).read_until(byte, buf)
    }

    #[inline]
    fn read_line(&mut self, buf: &mut String) -> io::Result<usize> {
        (**self).read_line(buf)
    }
}

// =============================================================================
// 内存中缓冲区的实现

/// 通过从切片复制为 `&[u8]` 实现读取。
///
/// 请注意，读取将更新切片以指向尚未读取的部分。
/// 到达 EOF 时，切片将为空。
#[stable(feature = "rust1", since = "1.0.0")]
impl Read for &[u8] {
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let amt = cmp::min(buf.len(), self.len());
        let (a, b) = self.split_at(amt);

        // 首先检查我们要读取的字节数是否很小：
        // `copy_from_slice` 通常会扩展为对 `memcpy` 的调用，并且对于单个字节来说，开销很大。
        //
        if amt == 1 {
            buf[0] = a[0];
        } else {
            buf[..amt].copy_from_slice(a);
        }

        *self = b;
        Ok(amt)
    }

    #[inline]
    fn read_buf(&mut self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
        let amt = cmp::min(cursor.capacity(), self.len());
        let (a, b) = self.split_at(amt);

        cursor.append(a);

        *self = b;
        Ok(())
    }

    #[inline]
    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        let mut nread = 0;
        for buf in bufs {
            nread += self.read(buf)?;
            if self.is_empty() {
                break;
            }
        }

        Ok(nread)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        true
    }

    #[inline]
    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        if buf.len() > self.len() {
            return Err(io::const_io_error!(
                ErrorKind::UnexpectedEof,
                "failed to fill whole buffer"
            ));
        }
        let (a, b) = self.split_at(buf.len());

        // 首先检查我们要读取的字节数是否很小：
        // `copy_from_slice` 通常会扩展为对 `memcpy` 的调用，并且对于单个字节来说，开销很大。
        //
        if buf.len() == 1 {
            buf[0] = a[0];
        } else {
            buf.copy_from_slice(a);
        }

        *self = b;
        Ok(())
    }

    #[inline]
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        buf.extend_from_slice(*self);
        let len = self.len();
        *self = &self[len..];
        Ok(len)
    }

    #[inline]
    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        let content = str::from_utf8(self).map_err(|_| {
            io::const_io_error!(ErrorKind::InvalidData, "stream did not contain valid UTF-8")
        })?;
        buf.push_str(content);
        let len = self.len();
        *self = &self[len..];
        Ok(len)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl BufRead for &[u8] {
    #[inline]
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        Ok(*self)
    }

    #[inline]
    fn consume(&mut self, amt: usize) {
        *self = &self[amt..];
    }
}

/// 通过将 `&mut [u8]` 复制到切片中并覆盖其数据来实现写入。
///
/// 请注意，编写会更新切片以指向尚未编写的部分。
/// 完全覆盖后，切片将为空。
///
/// 如果要写入的字节数超过了切片的大小，则写入操作将返回短写入：最终为 `Ok(0)`; 否则为 `Ok(0)`。在这种情况下，`write_all` 返回类型为 `ErrorKind::WriteZero` 的错误。
///
///
///
#[stable(feature = "rust1", since = "1.0.0")]
impl Write for &mut [u8] {
    #[inline]
    fn write(&mut self, data: &[u8]) -> io::Result<usize> {
        let amt = cmp::min(data.len(), self.len());
        let (a, b) = mem::take(self).split_at_mut(amt);
        a.copy_from_slice(&data[..amt]);
        *self = b;
        Ok(amt)
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let mut nwritten = 0;
        for buf in bufs {
            nwritten += self.write(buf)?;
            if self.is_empty() {
                break;
            }
        }

        Ok(nwritten)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        true
    }

    #[inline]
    fn write_all(&mut self, data: &[u8]) -> io::Result<()> {
        if self.write(data)? == data.len() {
            Ok(())
        } else {
            Err(io::const_io_error!(ErrorKind::WriteZero, "failed to write whole buffer"))
        }
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

/// 通过将 `Vec<u8>` 追加到 vector 来实现写入操作。
/// vector 将根据需要增长。
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Allocator> Write for Vec<u8, A> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.extend_from_slice(buf);
        Ok(buf.len())
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let len = bufs.iter().map(|b| b.len()).sum();
        self.reserve(len);
        for buf in bufs {
            self.extend_from_slice(buf);
        }
        Ok(len)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        true
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        self.extend_from_slice(buf);
        Ok(())
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

/// `VecDeque<u8>` 通过消耗 `VecDeque` 前面的字节来实现读取。
#[stable(feature = "vecdeque_read_write", since = "1.63.0")]
impl<A: Allocator> Read for VecDeque<u8, A> {
    /// 用 [`as_slices`][`VecDeque::as_slices`] 返回的 "front" 切片的内容填充 `buf`。
    /// 如果 `VecDeque` 包含的字节片不连续，则需要多次调用 `read` 来读取整个内容。
    ///
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let (ref mut front, _) = self.as_slices();
        let n = Read::read(front, buf)?;
        self.drain(..n);
        Ok(n)
    }

    #[inline]
    fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
        let (ref mut front, _) = self.as_slices();
        let n = cmp::min(cursor.capacity(), front.len());
        Read::read_buf(front, cursor)?;
        self.drain(..n);
        Ok(())
    }

    #[inline]
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        // 总长度是预先知道的，因此我们可以在单个调用中保留它。
        let len = self.len();
        buf.reserve(len);

        let (front, back) = self.as_slices();
        buf.extend_from_slice(front);
        buf.extend_from_slice(back);
        self.clear();
        Ok(len)
    }

    #[inline]
    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        // 我们必须使用一个连续的切片，因为 `VecDequeue` 可能会在 UTF-8 字符的中间被分割。
        //
        let len = self.len();
        let content = self.make_contiguous();
        let string = str::from_utf8(content).map_err(|_| {
            io::const_io_error!(ErrorKind::InvalidData, "stream did not contain valid UTF-8")
        })?;
        buf.push_str(string);
        self.clear();
        Ok(len)
    }
}

/// 通过，追加，到 `VecDeque` 来实现 `VecDeque<u8>` 的写入，并根据需要对其进行扩展。
#[stable(feature = "vecdeque_read_write", since = "1.63.0")]
impl<A: Allocator> Write for VecDeque<u8, A> {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.extend(buf);
        Ok(buf.len())
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let len = bufs.iter().map(|b| b.len()).sum();
        self.reserve(len);
        for buf in bufs {
            self.extend(&**buf);
        }
        Ok(len)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        true
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        self.extend(buf);
        Ok(())
    }

    #[inline]
    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}