//! Cross-platform interface to the `errno` variable.

#[cfg(unix)] extern crate libc;
#[cfg(windows)] extern crate winapi;
#[cfg(windows)] extern crate kernel32;

// FIXME(#10): Rust < 1.11 doesn't support cfg_attr on path
/*
#[cfg_attr(unix, path = "unix.rs")]
#[cfg_attr(windows, path = "windows.rs")]
mod sys;
*/

#[cfg(unix)] mod unix;
#[cfg(unix)] mod sys { pub use unix::*; }
#[cfg(windows)] mod windows;
#[cfg(windows)] mod sys { pub use windows::*; }

use std::fmt;

/// Wraps a platform-specific error code.
///
/// The `Display` instance maps the code to a human-readable string. It
/// calls [`strerror_r`][1] under POSIX, and [`FormatMessageW`][2] on
/// Windows.
///
/// [1]: http://pubs.opengroup.org/onlinepubs/009695399/functions/strerror.html
/// [2]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms679351%28v=vs.85%29.aspx
#[derive(Copy, Clone, Eq, Ord, PartialEq, PartialOrd, Hash)]
pub struct Errno(pub i32);

impl fmt::Debug for Errno {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        sys::with_description(*self, |desc| {
            fmt.debug_struct("Errno")
                .field("code", &self.0)
                .field("description", &desc.ok())
                .finish()
        })
    }
}

impl fmt::Display for Errno {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        sys::with_description(*self, |desc| match desc {
            Ok(desc) => fmt.write_str(&desc),
            Err(fm_err) => write!(
                fmt, "OS error {} ({} returned error {})",
                self.0, sys::STRERROR_NAME, fm_err.0),
        })
    }
}

/// Returns the platform-specific value of `errno`.
pub fn errno() -> Errno {
    sys::errno()
}

/// Sets the platform-specific value of `errno`.
pub fn set_errno(err: Errno) {
    sys::set_errno(err)
}

#[test]
fn it_works() {
    let x = errno();
    set_errno(x);
    let _ = x.to_string();
}

#[test]
fn check_description() {
    let expect = if cfg!(windows) {
        "Incorrect function."
    } else {
        "Operation not permitted"
    };

    set_errno(Errno(1));

    assert_eq!(errno().to_string(), expect);
    assert_eq!(
        format!("{:?}", errno()),
        format!("Errno {{ code: 1, description: Some({:?}) }}", expect));
}
