#![unstable(reason = "not public", issue = "none", feature = "fd")]

#[cfg(test)]
mod tests;

use crate::cmp;
use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read};
use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
use crate::sys::cvt;
use crate::sys_common::{AsInner, FromInner, IntoInner};

#[cfg(any(
    target_os = "android",
    target_os = "linux",
    target_os = "emscripten",
    target_os = "l4re"
))]
use libc::off64_t;
#[cfg(not(any(
    target_os = "linux",
    target_os = "emscripten",
    target_os = "l4re",
    target_os = "android"
)))]
use libc::off_t as off64_t;

#[derive(Debug)]
pub struct FileDesc(OwnedFd);

// 在大多数类似 POSIX 的系统上，最大读取限制为 `SSIZE_MAX`，手册页中引用了以下内容：如果要读取的字节数大于 `SSIZE_MAX`，则结果为 "unspecified"。
//
//
// 但是，在 macOS 上，显然 64 位 libc 是 buggy 或通过拒绝任何大小大于或等于 INT_MAX 的读取而有意显示奇怪的行为。
// 为了处理这两种情况，在两个平台上都限制了读取大小。
//
//
//
#[cfg(target_os = "macos")]
const READ_LIMIT: usize = libc::c_int::MAX as usize - 1;
#[cfg(not(target_os = "macos"))]
const READ_LIMIT: usize = libc::ssize_t::MAX as usize;

#[cfg(any(
    target_os = "dragonfly",
    target_os = "freebsd",
    target_os = "ios",
    target_os = "macos",
    target_os = "netbsd",
    target_os = "openbsd",
    target_os = "watchos",
))]
const fn max_iov() -> usize {
    libc::IOV_MAX as usize
}

#[cfg(any(
    target_os = "android",
    target_os = "emscripten",
    target_os = "linux",
    target_os = "nto",
))]
const fn max_iov() -> usize {
    libc::UIO_MAXIOV as usize
}

#[cfg(not(any(
    target_os = "android",
    target_os = "dragonfly",
    target_os = "emscripten",
    target_os = "freebsd",
    target_os = "ios",
    target_os = "linux",
    target_os = "macos",
    target_os = "netbsd",
    target_os = "nto",
    target_os = "openbsd",
    target_os = "horizon",
    target_os = "vita",
    target_os = "watchos",
)))]
const fn max_iov() -> usize {
    16 // POSIX 要求的最小值。
}

impl FileDesc {
    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::read(
                self.as_raw_fd(),
                buf.as_mut_ptr() as *mut libc::c_void,
                cmp::min(buf.len(), READ_LIMIT),
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(not(any(target_os = "espidf", target_os = "horizon", target_os = "vita")))]
    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::readv(
                self.as_raw_fd(),
                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(any(target_os = "espidf", target_os = "horizon", target_os = "vita"))]
    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        io::default_read_vectored(|b| self.read(b), bufs)
    }

    #[inline]
    pub fn is_read_vectored(&self) -> bool {
        cfg!(not(any(target_os = "espidf", target_os = "horizon", target_os = "vita")))
    }

    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
        let mut me = self;
        (&mut me).read_to_end(buf)
    }

    pub fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        #[cfg(not(any(target_os = "linux", target_os = "android")))]
        use libc::pread as pread64;
        #[cfg(any(target_os = "linux", target_os = "android"))]
        use libc::pread64;

        unsafe {
            cvt(pread64(
                self.as_raw_fd(),
                buf.as_mut_ptr() as *mut libc::c_void,
                cmp::min(buf.len(), READ_LIMIT),
                offset as off64_t,
            ))
            .map(|n| n as usize)
        }
    }

    pub fn read_buf(&self, mut cursor: BorrowedCursor<'_>) -> io::Result<()> {
        let ret = cvt(unsafe {
            libc::read(
                self.as_raw_fd(),
                cursor.as_mut().as_mut_ptr() as *mut libc::c_void,
                cmp::min(cursor.capacity(), READ_LIMIT),
            )
        })?;

        // 安全: `ret` 个字节被写入缓冲区的初始化部分
        unsafe {
            cursor.advance(ret as usize);
        }
        Ok(())
    }

    #[cfg(any(
        target_os = "emscripten",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "illumos",
        target_os = "linux",
        target_os = "netbsd",
    ))]
    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::preadv(
                self.as_raw_fd(),
                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
                offset as _,
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(not(any(
        target_os = "android",
        target_os = "emscripten",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "illumos",
        target_os = "ios",
        target_os = "linux",
        target_os = "macos",
        target_os = "netbsd",
    )))]
    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        io::default_read_vectored(|b| self.read_at(b, offset), bufs)
    }

    // 我们支持一些 libc 中没有 `preadv` 的旧 Android 版本，因此我们使用弱链接，如果不可用则回退到直接 syscall。
    //
    // 在 32 位目标上，我们不想处理将 64 位参数传递给系统调用的奇怪 ABI 问题，因此如果 `preadv` 不可用，我们将回退到默认实现。
    //
    //
    //
    #[cfg(all(target_os = "android", target_pointer_width = "64"))]
    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        super::weak::syscall! {
            fn preadv(
                fd: libc::c_int,
                iovec: *const libc::iovec,
                n_iovec: libc::c_int,
                offset: off64_t
            ) -> isize
        }

        let ret = cvt(unsafe {
            preadv(
                self.as_raw_fd(),
                bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
                offset as _,
            )
        })?;
        Ok(ret as usize)
    }

    // 我们支持没有 `preadv` 的旧 MacOS 和 iOS 版本。
    // 这些平台中不可能存在 `syscall`。
    #[cfg(any(
        all(target_os = "android", target_pointer_width = "32"),
        target_os = "ios",
        target_os = "macos",
    ))]
    pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        super::weak::weak!(fn preadv64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);

        match preadv64.get() {
            Some(preadv) => {
                let ret = cvt(unsafe {
                    preadv(
                        self.as_raw_fd(),
                        bufs.as_mut_ptr() as *mut libc::iovec as *const libc::iovec,
                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
                        offset as _,
                    )
                })?;
                Ok(ret as usize)
            }
            None => io::default_read_vectored(|b| self.read_at(b, offset), bufs),
        }
    }

    pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::write(
                self.as_raw_fd(),
                buf.as_ptr() as *const libc::c_void,
                cmp::min(buf.len(), READ_LIMIT),
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(not(any(target_os = "espidf", target_os = "horizon", target_os = "vita")))]
    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::writev(
                self.as_raw_fd(),
                bufs.as_ptr() as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(any(target_os = "espidf", target_os = "horizon", target_os = "vita"))]
    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        io::default_write_vectored(|b| self.write(b), bufs)
    }

    #[inline]
    pub fn is_write_vectored(&self) -> bool {
        cfg!(not(any(target_os = "espidf", target_os = "horizon", target_os = "vita")))
    }

    pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
        #[cfg(not(any(target_os = "linux", target_os = "android")))]
        use libc::pwrite as pwrite64;
        #[cfg(any(target_os = "linux", target_os = "android"))]
        use libc::pwrite64;

        unsafe {
            cvt(pwrite64(
                self.as_raw_fd(),
                buf.as_ptr() as *const libc::c_void,
                cmp::min(buf.len(), READ_LIMIT),
                offset as off64_t,
            ))
            .map(|n| n as usize)
        }
    }

    #[cfg(any(
        target_os = "emscripten",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "illumos",
        target_os = "linux",
        target_os = "netbsd",
    ))]
    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        let ret = cvt(unsafe {
            libc::pwritev(
                self.as_raw_fd(),
                bufs.as_ptr() as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
                offset as _,
            )
        })?;
        Ok(ret as usize)
    }

    #[cfg(not(any(
        target_os = "android",
        target_os = "emscripten",
        target_os = "freebsd",
        target_os = "fuchsia",
        target_os = "illumos",
        target_os = "ios",
        target_os = "linux",
        target_os = "macos",
        target_os = "netbsd",
    )))]
    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        io::default_write_vectored(|b| self.write_at(b, offset), bufs)
    }

    // 我们支持一些 libc 中没有 `pwritev` 的旧 Android 版本，因此我们使用弱链接，如果不可用则回退到直接 syscall。
    //
    // 在 32 位目标上，我们不想处理将 64 位参数传递给系统调用的奇怪 ABI 问题，因此如果 `pwritev` 不可用，我们将回退到默认实现。
    //
    //
    //
    #[cfg(all(target_os = "android", target_pointer_width = "64"))]
    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        super::weak::syscall! {
            fn pwritev(
                fd: libc::c_int,
                iovec: *const libc::iovec,
                n_iovec: libc::c_int,
                offset: off64_t
            ) -> isize
        }

        let ret = cvt(unsafe {
            pwritev(
                self.as_raw_fd(),
                bufs.as_ptr() as *const libc::iovec,
                cmp::min(bufs.len(), max_iov()) as libc::c_int,
                offset as _,
            )
        })?;
        Ok(ret as usize)
    }

    // 我们支持没有 `pwritev` 的旧 MacOS 和 iOS 版本。
    // 这些平台中不可能存在 `syscall`。
    #[cfg(any(
        all(target_os = "android", target_pointer_width = "32"),
        target_os = "ios",
        target_os = "macos",
    ))]
    pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        super::weak::weak!(fn pwritev64(libc::c_int, *const libc::iovec, libc::c_int, off64_t) -> isize);

        match pwritev64.get() {
            Some(pwritev) => {
                let ret = cvt(unsafe {
                    pwritev(
                        self.as_raw_fd(),
                        bufs.as_ptr() as *const libc::iovec,
                        cmp::min(bufs.len(), max_iov()) as libc::c_int,
                        offset as _,
                    )
                })?;
                Ok(ret as usize)
            }
            None => io::default_write_vectored(|b| self.write_at(b, offset), bufs),
        }
    }

    #[cfg(not(any(
        target_env = "newlib",
        target_os = "solaris",
        target_os = "illumos",
        target_os = "emscripten",
        target_os = "fuchsia",
        target_os = "l4re",
        target_os = "linux",
        target_os = "haiku",
        target_os = "redox",
        target_os = "vxworks",
        target_os = "nto",
    )))]
    pub fn set_cloexec(&self) -> io::Result<()> {
        unsafe {
            cvt(libc::ioctl(self.as_raw_fd(), libc::FIOCLEX))?;
            Ok(())
        }
    }
    #[cfg(any(
        all(target_env = "newlib", not(any(target_os = "espidf", target_os = "horizon"))),
        target_os = "solaris",
        target_os = "illumos",
        target_os = "emscripten",
        target_os = "fuchsia",
        target_os = "l4re",
        target_os = "linux",
        target_os = "haiku",
        target_os = "redox",
        target_os = "vxworks",
        target_os = "nto",
    ))]
    pub fn set_cloexec(&self) -> io::Result<()> {
        unsafe {
            let previous = cvt(libc::fcntl(self.as_raw_fd(), libc::F_GETFD))?;
            let new = previous | libc::FD_CLOEXEC;
            if new != previous {
                cvt(libc::fcntl(self.as_raw_fd(), libc::F_SETFD, new))?;
            }
            Ok(())
        }
    }
    #[cfg(any(target_os = "espidf", target_os = "horizon"))]
    pub fn set_cloexec(&self) -> io::Result<()> {
        // FD_CLOEXEC 在 ESP-IDF 和 Horizon OS 中不受支持，但没有必要，因为它们都不支持生成进程。
        //
        Ok(())
    }

    #[cfg(target_os = "linux")]
    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
        unsafe {
            let v = nonblocking as libc::c_int;
            cvt(libc::ioctl(self.as_raw_fd(), libc::FIONBIO, &v))?;
            Ok(())
        }
    }

    #[cfg(not(target_os = "linux"))]
    pub fn set_nonblocking(&self, nonblocking: bool) -> io::Result<()> {
        unsafe {
            let previous = cvt(libc::fcntl(self.as_raw_fd(), libc::F_GETFL))?;
            let new = if nonblocking {
                previous | libc::O_NONBLOCK
            } else {
                previous & !libc::O_NONBLOCK
            };
            if new != previous {
                cvt(libc::fcntl(self.as_raw_fd(), libc::F_SETFL, new))?;
            }
            Ok(())
        }
    }

    #[inline]
    pub fn duplicate(&self) -> io::Result<FileDesc> {
        Ok(Self(self.0.try_clone()?))
    }
}

impl<'a> Read for &'a FileDesc {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        (**self).read(buf)
    }

    fn read_buf(&mut self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
        (**self).read_buf(cursor)
    }

    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        (**self).read_vectored(bufs)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        (**self).is_read_vectored()
    }
}

impl AsInner<OwnedFd> for FileDesc {
    #[inline]
    fn as_inner(&self) -> &OwnedFd {
        &self.0
    }
}

impl IntoInner<OwnedFd> for FileDesc {
    fn into_inner(self) -> OwnedFd {
        self.0
    }
}

impl FromInner<OwnedFd> for FileDesc {
    fn from_inner(owned_fd: OwnedFd) -> Self {
        Self(owned_fd)
    }
}

impl AsFd for FileDesc {
    fn as_fd(&self) -> BorrowedFd<'_> {
        self.0.as_fd()
    }
}

impl AsRawFd for FileDesc {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.0.as_raw_fd()
    }
}

impl IntoRawFd for FileDesc {
    fn into_raw_fd(self) -> RawFd {
        self.0.into_raw_fd()
    }
}

impl FromRawFd for FileDesc {
    unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
        Self(FromRawFd::from_raw_fd(raw_fd))
    }
}