use crate::io::{AsyncSeek, SeekFrom};

use futures_core::future::Future;

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

use std::io;

use std::pin::Pin;

/// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.

#[derive(Debug)]

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

pub struct Seek<'a, S: ?Sized> {

    seek: &'a mut S,

    pos: SeekFrom,

}

impl<S: ?Sized + Unpin> Unpin for Seek<'_, S> {}

impl<'a, S: AsyncSeek + ?Sized + Unpin> Seek<'a, S> {

    pub(super) fn new(seek: &'a mut S, pos: SeekFrom) -> Self {

        Self { seek, pos }

    }

}

impl<S: AsyncSeek + ?Sized + Unpin> Future for Seek<'_, S> {

    type Output = io::Result<u64>;

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

        let this = &mut *self;

        Pin::new(&mut this.seek).poll_seek(cx, this.pos)

    }

}