#[cfg(unix)]
use async_std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
#[cfg(windows)]
use async_std::os::windows::io::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
use async_std::{
    fs, io,
    task::{Context, Poll},
};
use std::pin::Pin;

/// A reference to an open file on a filesystem.
///
/// This corresponds to [`std::fs::File`].
///
/// Note that this `File` has no `open` or `create` methods. To open or create
/// a file, you must first obtain a [`Dir`] containing the path, and then call
/// [`Dir::open_file`] or [`Dir::create_file`].
///
/// [`std::fs::File`]: https://doc.rust-lang.org/std/fs/struct.File.html
/// [`Dir`]: struct.Dir.html
/// [`Dir::open_file`]: struct.Dir.html#method.open_file
/// [`Dir::create_file`]: struct.Dir.html#method.create_file
pub struct File {
    std: fs::File,
}

impl File {
    /// Constructs a new instance of `Self` from the given `async_std::fs::File`.
    #[inline]
    pub fn from_std(std: fs::File) -> Self {
        Self { std }
    }

    /// Attempts to sync all OS-internal metadata to disk.
    ///
    /// This corresponds to [`std::fs::File::sync_all`].
    ///
    /// [`std::fs::File::sync_all`]: https://doc.rust-lang.org/std/fs/struct.File.html#method.sync_all
    #[inline]
    pub async fn sync_all(&self) -> io::Result<()> {
        self.std.sync_all().await
    }

    /// This function is similar to `sync_all`, except that it may not synchronize
    /// file metadata to a filesystem.
    ///
    /// This corresponds to [`std::fs::File::sync_data`].
    ///
    /// [`std::fs::File::sync_data`]: https://doc.rust-lang.org/std/fs/struct.File.html#method.sync_data
    #[inline]
    pub async fn sync_data(&self) -> io::Result<()> {
        self.std.sync_data().await
    }

    /// Truncates or extends the underlying file, updating the size of this file
    /// to become size.
    ///
    /// This corresponds to [`std::fs::File::set_len`].
    ///
    /// [`std::fs::File::set_len`]: https://doc.rust-lang.org/std/fs/struct.File.html#method.set_len
    #[inline]
    pub async fn set_len(&self, size: u64) -> io::Result<()> {
        self.std.set_len(size).await
    }

    /// Queries metadata about the underlying file.
    ///
    /// This corresponds to [`std::fs::File::metadata`].
    ///
    /// [`std::fs::File::metadata`]: https://doc.rust-lang.org/std/fs/struct.File.html#method.metadata
    #[inline]
    pub async fn metadata(&self) -> io::Result<fs::Metadata> {
        self.std.metadata().await
    }

    // async_std doesn't have `try_clone`.
}

#[cfg(unix)]
impl FromRawFd for File {
    #[inline]
    unsafe fn from_raw_fd(fd: RawFd) -> Self {
        Self::from_std(fs::File::from_raw_fd(fd))
    }
}

#[cfg(windows)]
impl FromRawHandle for File {
    #[inline]
    unsafe fn from_raw_handle(handle: RawHandle) -> Self {
        Self::from_std(fs::File::from_raw_handle(handle))
    }
}

#[cfg(unix)]
impl AsRawFd for File {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.std.as_raw_fd()
    }
}

#[cfg(windows)]
impl AsRawHandle for File {
    #[inline]
    fn as_raw_handle(&self) -> RawHandle {
        self.std.as_raw_handle()
    }
}

#[cfg(unix)]
impl IntoRawFd for File {
    #[inline]
    fn into_raw_fd(self) -> RawFd {
        self.std.into_raw_fd()
    }
}

#[cfg(windows)]
impl IntoRawHandle for File {
    #[inline]
    fn into_raw_handle(self) -> RawHandle {
        self.std.into_raw_handle()
    }
}

impl io::Read for File {
    #[inline]
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        buf: &mut [u8],
    ) -> Poll<io::Result<usize>> {
        io::Read::poll_read(Pin::new(&mut self.std), cx, buf)
    }

    #[inline]
    fn poll_read_vectored(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        bufs: &mut [io::IoSliceMut],
    ) -> Poll<io::Result<usize>> {
        io::Read::poll_read_vectored(Pin::new(&mut self.std), cx, bufs)
    }

    // TODO: nightly-only APIs initializer?
}

impl io::Write for File {
    #[inline]
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        io::Write::poll_write(Pin::new(&mut self.std), cx, buf)
    }

    #[inline]
    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
        io::Write::poll_flush(Pin::new(&mut self.std), cx)
    }

    #[inline]
    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<io::Result<()>> {
        io::Write::poll_close(Pin::new(&mut self.std), cx)
    }

    #[inline]
    fn poll_write_vectored(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        bufs: &[io::IoSlice],
    ) -> Poll<io::Result<usize>> {
        io::Write::poll_write_vectored(Pin::new(&mut self.std), cx, bufs)
    }
}

impl io::Seek for File {
    #[inline]
    fn poll_seek(
        mut self: Pin<&mut Self>,
        cx: &mut Context,
        pos: io::SeekFrom,
    ) -> Poll<io::Result<u64>> {
        io::Seek::poll_seek(Pin::new(&mut self.std), cx, pos)
    }

    // TODO: nightly-only APIs stream_len, stream_position?
}

// TODO: Can async_std implement `From<File>` for `process::Stdio`?

// async_std doesn't have `FileExt`.

// TODO: Use winx to implement "unix" FileExt api on Windows?

// TODO: impl Debug for File? But don't expose File's path...