use super::{copy_buf, BufReader, CopyBuf};

use futures_core::future::Future;

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

use futures_io::{AsyncRead, AsyncWrite};

use pin_project_lite::pin_project;

use std::io;

use std::pin::Pin;

/// Creates a future which copies all the bytes from one object to another.

///

/// The returned future will copy all the bytes read from this `AsyncRead` into the

/// `writer` specified. This future will only complete once the `reader` has hit

/// EOF and all bytes have been written to and flushed from the `writer`

/// provided.

///

/// On success the number of bytes is returned.

///

/// # Examples

///

/// ```

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

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

///

/// let reader = Cursor::new([1, 2, 3, 4]);

/// let mut writer = Cursor::new(vec![0u8; 5]);

///

/// let bytes = io::copy(reader, &mut writer).await?;

/// writer.close().await?;

///

/// assert_eq!(bytes, 4);

/// assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);

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

/// ```

pub fn copy<R, W>(reader: R, writer: &mut W) -> Copy<'_, R, W>

where

    R: AsyncRead,

    W: AsyncWrite + Unpin + ?Sized,

{

    Copy { inner: copy_buf(BufReader::new(reader), writer) }

}

pin_project! {

    /// Future for the [`copy()`] function.

    #[derive(Debug)]

    #[must_use = "futures do nothing unless you `.await` or poll them"]

    pub struct Copy<'a, R, W: ?Sized> {

        #[pin]

        inner: CopyBuf<'a, BufReader<R>, W>,

    }

}

impl<R: AsyncRead, W: AsyncWrite + Unpin + ?Sized> Future for Copy<'_, R, W> {

    type Output = io::Result<u64>;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {

        self.project().inner.poll(cx)

    }

}