carapace 0.2.0

use std::ffi::{CStr, CString};
use std::mem::MaybeUninit;

use std::{io, ptr, slice};

use nix::NixPath;

pub type RawFd = std::os::unix::io::RawFd;

pub fn libc_call(f: impl FnOnce() -> i32) -> io::Result<u32> {
    let ret = f();
    if ret < 0 {
        return Err(io::Error::last_os_error());
    }
    Ok(ret as u32)
}

pub fn is_dir(path: &(impl NixPath + ?Sized)) -> nix::Result<bool> {
    nix::sys::stat::stat(path).map(|stat| stat.st_mode & libc::S_IFMT == libc::S_IFDIR)
}

pub fn with_c_str<T>(bytes: &[u8], f: impl FnOnce(&CStr) -> io::Result<T>) -> io::Result<T> {
    /// The threshold of allocation
    #[allow(clippy::as_conversions)]
    const STACK_BUF_SIZE: usize = libc::PATH_MAX as usize; // 4096

    if memchr::memchr(0, bytes).is_some() {
        let err = io::Error::new(
            io::ErrorKind::InvalidInput,
            "input bytes contain an interior nul byte",
        );
        return Err(err);
    }

    if bytes.len() >= STACK_BUF_SIZE {
        let c_string = unsafe { CString::from_vec_unchecked(Vec::from(bytes)) };
        return f(&c_string);
    }

    let mut buf: MaybeUninit<[u8; STACK_BUF_SIZE]> = MaybeUninit::uninit();

    unsafe {
        let buf: *mut u8 = buf.as_mut_ptr().cast();
        ptr::copy_nonoverlapping(bytes.as_ptr(), buf, bytes.len());
        buf.add(bytes.len()).write(0);

        let bytes_with_nul = slice::from_raw_parts(buf, bytes.len().wrapping_add(1));
        let c_str = CStr::from_bytes_with_nul_unchecked(bytes_with_nul);

        f(c_str)
    }
}