//! Functions which operate on file descriptors which might be terminals.

use crate::backend;

#[cfg(feature = "alloc")]

#[cfg(feature = "fs")]

#[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]

use crate::path::SMALL_PATH_BUFFER_SIZE;

use backend::fd::AsFd;

#[cfg(feature = "alloc")]

#[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]

use {crate::ffi::CString, crate::io, alloc::vec::Vec, backend::fd::BorrowedFd};

/// `isatty(fd)`—Tests whether a file descriptor refers to a terminal.

///

/// # References

///  - [POSIX]

///  - [Linux]

///

/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/isatty.html

/// [Linux]: https://man7.org/linux/man-pages/man3/isatty.3.html

#[inline]

pub fn isatty<Fd: AsFd>(fd: Fd) -> bool {

    backend::termios::syscalls::isatty(fd.as_fd())

}

/// `ttyname_r(fd)`—Returns the name of the tty open on `fd`.

///

/// If `reuse` already has available capacity, reuse it if possible.

///

/// On Linux, this function depends on procfs being mounted on /proc.

///

/// # References

///  - [POSIX]

///  - [Linux]

///

/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9799919799/functions/ttyname.html

/// [Linux]: https://man7.org/linux/man-pages/man3/ttyname.3.html

#[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]

#[cfg(feature = "alloc")]

#[cfg(feature = "fs")]

#[doc(alias = "ttyname_r")]

#[cfg_attr(docsrs, doc(cfg(feature = "fs")))]

#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]

#[inline]

pub fn ttyname<Fd: AsFd, B: Into<Vec<u8>>>(fd: Fd, reuse: B) -> io::Result<CString> {

    _ttyname(fd.as_fd(), reuse.into())

}

#[cfg(not(any(target_os = "fuchsia", target_os = "wasi")))]

#[cfg(feature = "alloc")]

#[cfg(feature = "fs")]

#[allow(unsafe_code)]

fn _ttyname(fd: BorrowedFd<'_>, mut buffer: Vec<u8>) -> io::Result<CString> {

    buffer.clear();

    buffer.reserve(SMALL_PATH_BUFFER_SIZE);

    loop {

        match backend::termios::syscalls::ttyname(fd, buffer.spare_capacity_mut()) {

            Err(io::Errno::RANGE) => {

                // Use `Vec` reallocation strategy to grow capacity

                // exponentially.

                buffer.reserve(buffer.capacity() + 1);

            }

            Ok(len) => {

                // SAFETY: Assume the backend returns the length of the string

                // excluding the NUL.

                unsafe {

                    buffer.set_len(len + 1);

                }

                // SAFETY:

                // - “ttyname_r stores this pathname in the buffer buf”

                // - [POSIX definition 3.271: Pathname]: “A string that is

                //   used to identify a file.”

                // - [POSIX definition 3.375: String]: “A contiguous sequence

                //   of bytes terminated by and including the first null byte.”

                //

                // Thus, there will be a single NUL byte at the end of the

                // string.

                //

                // [POSIX definition 3.271: Pathname]: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap03.html#tag_03_271

                // [POSIX definition 3.375: String]: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap03.html#tag_03_375

                unsafe {

                    return Ok(CString::from_vec_with_nul_unchecked(buffer));

                }

            }

            Err(errno) => return Err(errno),

        }

    }

}