use crate::io::blocking::Blocking;

use crate::io::stdio_common::SplitByUtf8BoundaryIfWindows;

use crate::io::AsyncWrite;

use std::io;

use std::pin::Pin;

use std::task::Context;

use std::task::Poll;

cfg_io_std! {

    /// A handle to the standard error stream of a process.

    ///

    /// Concurrent writes to stderr must be executed with care: Only individual

    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular

    /// you should be aware that writes using [`write_all`] are not guaranteed

    /// to occur as a single write, so multiple threads writing data with

    /// [`write_all`] may result in interleaved output.

    ///

    /// Created by the [`stderr`] function.

    ///

    /// [`stderr`]: stderr()

    /// [`AsyncWrite`]: AsyncWrite

    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()

    ///

    /// # Examples

    ///

    /// ```

    /// use tokio::io::{self, AsyncWriteExt};

    ///

    /// #[tokio::main]

    /// async fn main() -> io::Result<()> {

    ///     let mut stderr = io::stderr();

    ///     stderr.write_all(b"Print some error here.").await?;

    ///     Ok(())

    /// }

    /// ```

    #[derive(Debug)]

    pub struct Stderr {

        std: SplitByUtf8BoundaryIfWindows<Blocking<std::io::Stderr>>,

    }

    /// Constructs a new handle to the standard error of the current process.

    ///

    /// The returned handle allows writing to standard error from the within the

    /// Tokio runtime.

    ///

    /// Concurrent writes to stderr must be executed with care: Only individual

    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular

    /// you should be aware that writes using [`write_all`] are not guaranteed

    /// to occur as a single write, so multiple threads writing data with

    /// [`write_all`] may result in interleaved output.

    ///

    /// Note that unlike [`std::io::stderr`], each call to this `stderr()`

    /// produces a new writer, so for example, this program does **not** flush stderr:

    ///

    /// ```no_run

    /// # use tokio::io::AsyncWriteExt;

    /// # #[tokio::main]

    /// # async fn main() -> std::io::Result<()> {

    /// tokio::io::stderr().write_all(b"aa").await?;

    /// tokio::io::stderr().flush().await?;

    /// # Ok(())

    /// # }

    /// ```

    ///

    /// [`std::io::stderr`]: std::io::stderr

    /// [`AsyncWrite`]: AsyncWrite

    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()

    ///

    /// # Examples

    ///

    /// ```

    /// use tokio::io::{self, AsyncWriteExt};

    ///

    /// #[tokio::main]

    /// async fn main() -> io::Result<()> {

    ///     let mut stderr = io::stderr();

    ///     stderr.write_all(b"Print some error here.").await?;

    ///     Ok(())

    /// }

    /// ```

    pub fn stderr() -> Stderr {

        let std = io::stderr();

        // SAFETY: The `Read` implementation of `std` does not read from the

        // buffer it is borrowing and correctly reports the length of the data

        // written into the buffer.

        let blocking = unsafe { Blocking::new(std) };

        Stderr {

            std: SplitByUtf8BoundaryIfWindows::new(blocking),

        }

    }

}

#[cfg(unix)]

mod sys {

    use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};

    use super::Stderr;

    impl AsRawFd for Stderr {

        fn as_raw_fd(&self) -> RawFd {

            std::io::stderr().as_raw_fd()

        }

    }

    impl AsFd for Stderr {

        fn as_fd(&self) -> BorrowedFd<'_> {

            unsafe { BorrowedFd::borrow_raw(self.as_raw_fd()) }

        }

    }

}

cfg_windows! {

    use crate::os::windows::io::{AsHandle, BorrowedHandle, AsRawHandle, RawHandle};

    impl AsRawHandle for Stderr {

        fn as_raw_handle(&self) -> RawHandle {

            std::io::stderr().as_raw_handle()

        }

    }

    impl AsHandle for Stderr {

        fn as_handle(&self) -> BorrowedHandle<'_> {

            unsafe { BorrowedHandle::borrow_raw(self.as_raw_handle()) }

        }

    }

}

impl AsyncWrite for Stderr {

    fn poll_write(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

        buf: &[u8],

    ) -> Poll<io::Result<usize>> {

        Pin::new(&mut self.std).poll_write(cx, buf)

    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {

        Pin::new(&mut self.std).poll_flush(cx)

    }

    fn poll_shutdown(

        mut self: Pin<&mut Self>,

        cx: &mut Context<'_>,

    ) -> Poll<Result<(), io::Error>> {

        Pin::new(&mut self.std).poll_shutdown(cx)

    }

}