use core::cmp;

use crate::alloc::Allocator;
use crate::boxed::Box;
#[cfg(not(no_global_oom_handling))]
use crate::collections::VecDeque;
use crate::fmt;
use crate::io::{
    self, BorrowedCursor, BufRead, IoSlice, IoSliceMut, Read, Seek, SeekFrom, SizeHint, Write,
};
use crate::string::String;
#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
use crate::sync::Arc;
use crate::vec::Vec;

// =============================================================================
// Forwarding implementations

#[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<'_, u8>) -> 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)
    }

    #[inline]
    fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        (**self).read_buf_exact(cursor)
    }
}
#[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 has_data_left(&mut self) -> io::Result<bool> {
        (**self).has_data_left()
    }

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

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

    #[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<'_, u8>) -> 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)
    }

    #[inline]
    fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        (**self).read_buf_exact(cursor)
    }
}
#[doc(hidden)]
#[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
impl<T> SizeHint for Box<T> {
    #[inline]
    fn lower_bound(&self) -> usize {
        SizeHint::lower_bound(&**self)
    }

    #[inline]
    fn upper_bound(&self) -> Option<usize> {
        SizeHint::upper_bound(&**self)
    }
}

#[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_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
        (**self).write_all_vectored(bufs)
    }

    #[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 rewind(&mut self) -> io::Result<()> {
        (**self).rewind()
    }

    #[inline]
    fn stream_len(&mut self) -> io::Result<u64> {
        (**self).stream_len()
    }

    #[inline]
    fn stream_position(&mut self) -> io::Result<u64> {
        (**self).stream_position()
    }

    #[inline]
    fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
        (**self).seek_relative(offset)
    }
}
#[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 has_data_left(&mut self) -> io::Result<bool> {
        (**self).has_data_left()
    }

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

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

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

// =============================================================================
// In-memory buffer implementations

/// Read is implemented for `&[u8]` by copying from the slice.
///
/// Note that reading updates the slice to point to the yet unread part.
/// The slice will be empty when EOF is reached.
#[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);

        // First check if the amount of bytes we want to read is small:
        // `copy_from_slice` will generally expand to a call to `memcpy`, and
        // for a single byte the overhead is significant.
        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<'_, u8>) -> 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() {
            // `read_exact` makes no promise about the content of `buf` if it
            // fails so don't bother about that.
            *self = &self[self.len()..];
            return Err(io::Error::READ_EXACT_EOF);
        }
        let (a, b) = self.split_at(buf.len());

        // First check if the amount of bytes we want to read is small:
        // `copy_from_slice` will generally expand to a call to `memcpy`, and
        // for a single byte the overhead is significant.
        if buf.len() == 1 {
            buf[0] = a[0];
        } else {
            buf.copy_from_slice(a);
        }

        *self = b;
        Ok(())
    }

    #[inline]
    fn read_buf_exact(&mut self, mut cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        if cursor.capacity() > self.len() {
            // Append everything we can to the cursor.
            cursor.append(*self);
            *self = &self[self.len()..];
            return Err(io::Error::READ_EXACT_EOF);
        }
        let (a, b) = self.split_at(cursor.capacity());

        cursor.append(a);

        *self = b;
        Ok(())
    }

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

        cfg_select! {
            no_global_oom_handling => {
                buf.try_extend_from_slice_of_bytes(*self)?;
            }
            _ => {
                buf.extend_from_slice(*self);
            }
        }

        *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::Error::INVALID_UTF8)?;
        let len = self.len();
        buf.try_reserve(len)?;

        cfg_select! {
            no_global_oom_handling => {
                buf.try_push_str(content)?;
            }
            _ => {
                buf.push_str(content);
            }
        }

        *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..];
    }
}

/// Write is implemented for `Vec<u8>` by appending to the vector.
/// The vector will grow as needed.
#[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 as Write>::write_all(self, buf)?;
        Ok(buf.len())
    }

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

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

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        cfg_select! {
            no_global_oom_handling => {
                self.try_extend_from_slice_of_bytes(buf)?;
            }
            _ => {
                self.extend_from_slice(buf);
            }
        }
        Ok(())
    }

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

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

/// Read is implemented for `VecDeque<u8>` by consuming bytes from the front of the `VecDeque`.
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vecdeque_read_write", since = "1.63.0")]
impl<A: Allocator> Read for VecDeque<u8, A> {
    /// Fill `buf` with the contents of the "front" slice as returned by
    /// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` are
    /// discontiguous, multiple calls to `read` will be needed to read the entire content.
    #[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_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        let (front, back) = self.as_slices();

        // Use only the front buffer if it is big enough to fill `buf`, else use
        // the back buffer too.
        match buf.split_at_mut_checked(front.len()) {
            None => buf.copy_from_slice(&front[..buf.len()]),
            Some((buf_front, buf_back)) => match back.split_at_checked(buf_back.len()) {
                Some((back, _)) => {
                    buf_front.copy_from_slice(front);
                    buf_back.copy_from_slice(back);
                }
                None => {
                    self.clear();
                    return Err(io::Error::READ_EXACT_EOF);
                }
            },
        }

        self.drain(..buf.len());
        Ok(())
    }

    #[inline]
    fn read_buf(&mut self, cursor: BorrowedCursor<'_, u8>) -> 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_buf_exact(&mut self, mut cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        let len = cursor.capacity();
        let (front, back) = self.as_slices();

        match front.split_at_checked(cursor.capacity()) {
            Some((front, _)) => cursor.append(front),
            None => {
                cursor.append(front);
                match back.split_at_checked(cursor.capacity()) {
                    Some((back, _)) => cursor.append(back),
                    None => {
                        cursor.append(back);
                        self.clear();
                        return Err(io::Error::READ_EXACT_EOF);
                    }
                }
            }
        }

        self.drain(..len);
        Ok(())
    }

    #[inline]
    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
        // The total len is known upfront so we can reserve it in a single call.
        let len = self.len();
        buf.try_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> {
        // SAFETY: We only append to the buffer
        unsafe { io::append_to_string(buf, |buf| self.read_to_end(buf)) }
    }
}

/// BufRead is implemented for `VecDeque<u8>` by reading bytes from the front of the `VecDeque`.
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "vecdeque_buf_read", since = "1.75.0")]
impl<A: Allocator> BufRead for VecDeque<u8, A> {
    /// Returns the contents of the "front" slice as returned by
    /// [`as_slices`][`VecDeque::as_slices`]. If the contained byte slices of the `VecDeque` are
    /// discontiguous, multiple calls to `fill_buf` will be needed to read the entire content.
    #[inline]
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        let (front, _) = self.as_slices();
        Ok(front)
    }

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

/// Write is implemented for `VecDeque<u8>` by appending to the `VecDeque`, growing it as needed.
#[cfg(not(no_global_oom_handling))]
#[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 write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
        self.write_vectored(bufs)?;
        Ok(())
    }

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

#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
#[stable(feature = "io_traits_arc", since = "1.73.0")]
impl<R: Read + ?Sized> Read for Arc<R>
where
    for<'a> &'a R: Read,
    R: crate::io::IoHandle,
{
    #[inline]
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        (&**self).read(buf)
    }

    #[inline]
    fn read_buf(&mut self, cursor: BorrowedCursor<'_, u8>) -> 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)
    }

    #[inline]
    fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_, u8>) -> io::Result<()> {
        (&**self).read_buf_exact(cursor)
    }
}
#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
#[stable(feature = "io_traits_arc", since = "1.73.0")]
impl<W: Write + ?Sized> Write for Arc<W>
where
    for<'a> &'a W: Write,
    W: crate::io::IoHandle,
{
    #[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_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> io::Result<()> {
        (&**self).write_all_vectored(bufs)
    }

    #[inline]
    fn write_fmt(&mut self, fmt: fmt::Arguments<'_>) -> io::Result<()> {
        (&**self).write_fmt(fmt)
    }
}
#[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
#[stable(feature = "io_traits_arc", since = "1.73.0")]
impl<S: Seek + ?Sized> Seek for Arc<S>
where
    for<'a> &'a S: Seek,
    S: crate::io::IoHandle,
{
    #[inline]
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        (&**self).seek(pos)
    }

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

    #[inline]
    fn stream_len(&mut self) -> io::Result<u64> {
        (&**self).stream_len()
    }

    #[inline]
    fn stream_position(&mut self) -> io::Result<u64> {
        (&**self).stream_position()
    }

    #[inline]
    fn seek_relative(&mut self, offset: i64) -> io::Result<()> {
        (&**self).seek_relative(offset)
    }
}