use crate::io::seek::{seek, Seek};
use crate::io::AsyncSeek;
use std::io::SeekFrom;

/// An extension trait which adds utility methods to [`AsyncSeek`] types.
///
/// As a convenience, this trait may be imported using the [`prelude`]:
///
/// # Examples
///
/// ```
/// use std::io::{Cursor, SeekFrom};
/// use tokio::prelude::*;
///
/// #[tokio::main]
/// async fn main() -> io::Result<()> {
///     let mut cursor = Cursor::new(b"abcdefg");
///
///     // the `seek` method is defined by this trait
///     cursor.seek(SeekFrom::Start(3)).await?;
///
///     let mut buf = [0; 1];
///     let n = cursor.read(&mut buf).await?;
///     assert_eq!(n, 1);
///     assert_eq!(buf, [b'd']);
///
///     Ok(())
/// }
/// ```
///
/// See [module][crate::io] documentation for more details.
///
/// [`AsyncSeek`]: AsyncSeek
/// [`prelude`]: crate::prelude
pub trait AsyncSeekExt: AsyncSeek {
    /// Creates a future which will seek an IO object, and then yield the
    /// new position in the object and the object itself.
    ///
    /// In the case of an error the buffer and the object will be discarded, with
    /// the error yielded.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::File;
    /// use tokio::prelude::*;
    ///
    /// use std::io::SeekFrom;
    ///
    /// # async fn dox() -> std::io::Result<()> {
    /// let mut file = File::open("foo.txt").await?;
    /// file.seek(SeekFrom::Start(6)).await?;
    ///
    /// let mut contents = vec![0u8; 10];
    /// file.read_exact(&mut contents).await?;
    /// # Ok(())
    /// # }
    /// ```
    fn seek(&mut self, pos: SeekFrom) -> Seek<'_, Self>
    where
        Self: Unpin,
    {
        seek(self, pos)
    }
}

impl<S: AsyncSeek + ?Sized> AsyncSeekExt for S {}