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 output stream of a process.

    ///

    /// Concurrent writes to stdout 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.

    ///

    /// # Warning

    ///

    /// Each call to [`stdout()`] creates a **new** handle with its own

    /// internal state. Writes through different handles are not

    /// coordinated, so creating a new handle in a loop can cause output

    /// to appear out of order:

    ///

    /// ```no_run

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

    /// # #[tokio::main]

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

    /// // WRONG: creates a new handle each iteration

    /// for i in 0..10 {

    ///     let mut out = io::stdout();

    ///     out.write_all(b"data").await?;

    ///     out.write_all(b"\n").await?;

    ///     // out is dropped here; its last write may still be

    ///     // running when the next iteration starts

    /// }

    /// # Ok(())

    /// # }

    /// ```

    ///

    /// To preserve order, create one handle outside the loop and

    /// reuse it:

    ///

    /// ```no_run

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

    /// # #[tokio::main]

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

    /// let mut out = io::stdout();

    /// for i in 0..10 {

    ///     out.write_all(b"data").await?;

    ///     out.write_all(b"\n").await?;

    /// }

    /// # Ok(())

    /// # }

    /// ```

    ///

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

    ///

    /// [`stdout`]: stdout()

    /// [`AsyncWrite`]: AsyncWrite

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

    ///

    /// # Examples

    ///

    /// ```

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

    ///

    /// #[tokio::main]

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

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

    ///     stdout.write_all(b"Hello world!").await?;

    ///     Ok(())

    /// }

    /// ```

    ///

    /// The following is an example of using `stdio` with loop.

    ///

    /// ```

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

    ///

    /// #[tokio::main]

    /// async fn main() {

    ///     let messages = vec!["hello", " world\n"];

    ///

    ///     // When you use `stdio` in a loop, it is recommended to create

    ///     // a single `stdio` instance outside the loop and call a write

    ///     // operation against that instance on each loop.

    ///     //

    ///     // Repeatedly creating `stdout` instances inside the loop and

    ///     // writing to that handle could result in mangled output since

    ///     // each write operation is handled by a different blocking thread.

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

    ///

    ///     for message in &messages {

    ///         stdout.write_all(message.as_bytes()).await.unwrap();

    ///         stdout.flush().await.unwrap();

    ///     }

    /// }

    /// ```

    #[derive(Debug)]

    pub struct Stdout {

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

    }

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

    ///

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

    /// Tokio runtime.

    ///

    /// Concurrent writes to stdout 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::stdout`], each call to this `stdout()`

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

    ///

    /// ```no_run

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

    /// # #[tokio::main]

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

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

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

    /// # Ok(())

    /// # }

    /// ```

    ///

    /// [`std::io::stdout`]: std::io::stdout

    /// [`AsyncWrite`]: AsyncWrite

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

    ///

    /// # Examples

    ///

    /// ```

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

    ///

    /// #[tokio::main]

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

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

    ///     stdout.write_all(b"Hello world!").await?;

    ///     Ok(())

    /// }

    /// ```

    ///

    /// The following is an example of using `stdio` with loop.

    ///

    /// ```

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

    ///

    /// #[tokio::main]

    /// async fn main() {

    ///     let messages = vec!["hello", " world\n"];

    ///

    ///     // When you use `stdio` in a loop, it is recommended to create

    ///     // a single `stdio` instance outside the loop and call a write

    ///     // operation against that instance on each loop.

    ///     //

    ///     // Repeatedly creating `stdout` instances inside the loop and

    ///     // writing to that handle could result in mangled output since

    ///     // each write operation is handled by a different blocking thread.

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

    ///

    ///     for message in &messages {

    ///         stdout.write_all(message.as_bytes()).await.unwrap();

    ///         stdout.flush().await.unwrap();

    ///     }

    /// }

    /// ```

    pub fn stdout() -> Stdout {

        let std = io::stdout();

        // 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) };

        Stdout {

            std: SplitByUtf8BoundaryIfWindows::new(blocking),

        }

    }

}

#[cfg(unix)]

mod sys {

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

    use super::Stdout;

    impl AsRawFd for Stdout {

        fn as_raw_fd(&self) -> RawFd {

            std::io::stdout().as_raw_fd()

        }

    }

    impl AsFd for Stdout {

        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 Stdout {

        fn as_raw_handle(&self) -> RawHandle {

            std::io::stdout().as_raw_handle()

        }

    }

    impl AsHandle for Stdout {

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

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

        }

    }

}

impl AsyncWrite for Stdout {

    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)

    }

}