use futures_core::task::{Context, Poll};

use futures_io::{AsyncWrite, IoSlice};

use std::fmt;

use std::io;

use std::pin::Pin;

/// Writer for the [`sink()`] function.

#[must_use = "writers do nothing unless polled"]

pub struct Sink {

    _priv: (),

}

/// Creates an instance of a writer which will successfully consume all data.

///

/// All calls to `poll_write` on the returned instance will return `Poll::Ready(Ok(buf.len()))`

/// and the contents of the buffer will not be inspected.

///

/// # Examples

///

/// ```rust

/// # futures::executor::block_on(async {

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

///

/// let buffer = vec![1, 2, 3, 5, 8];

/// let mut writer = io::sink();

/// let num_bytes = writer.write(&buffer).await?;

/// assert_eq!(num_bytes, 5);

/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();

/// ```

pub fn sink() -> Sink {

    Sink { _priv: () }

}

impl AsyncWrite for Sink {

    #[inline]

    fn poll_write(

        self: Pin<&mut Self>,

        _: &mut Context<'_>,

        buf: &[u8],

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

        Poll::Ready(Ok(buf.len()))

    }

    #[inline]

    fn poll_write_vectored(

        self: Pin<&mut Self>,

        _: &mut Context<'_>,

        bufs: &[IoSlice<'_>],

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

        Poll::Ready(Ok(bufs.iter().map(|b| b.len()).sum()))

    }

    #[inline]

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

        Poll::Ready(Ok(()))

    }

    #[inline]

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

        Poll::Ready(Ok(()))

    }

}

impl fmt::Debug for Sink {

    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

        f.pad("Sink { .. }")

    }

}