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// Copyright (c) 2017 CtrlC developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

use crate::error::Error as CtrlcError;
use nix::unistd;
use std::os::unix::io::RawFd;
use std::future::Future;

static mut PIPE: (RawFd, RawFd) = (-1, -1);

/// Platform specific error type
pub type Error = nix::Error;

/// Platform specific signal type
pub type Signal = nix::sys::signal::Signal;

extern "C" fn os_handler(_: nix::libc::c_int) {
    // Assuming this always succeeds. Can't really handle errors in any meaningful way.
    unsafe {
        let _ = unistd::write(PIPE.1, &[0u8]);
    }
}

// pipe2(2) is not available on macOS or iOS, so we need to use pipe(2) and fcntl(2)
#[inline]
#[cfg(any(target_os = "ios", target_os = "macos"))]
fn pipe2(flags: nix::fcntl::OFlag) -> nix::Result<(RawFd, RawFd)> {
    use nix::fcntl::{fcntl, FcntlArg, FdFlag, OFlag};

    let pipe = unistd::pipe()?;

    let mut res = Ok(0);

    if flags.contains(OFlag::O_CLOEXEC) {
        res = res
            .and_then(|_| fcntl(pipe.0, FcntlArg::F_SETFD(FdFlag::FD_CLOEXEC)))
            .and_then(|_| fcntl(pipe.1, FcntlArg::F_SETFD(FdFlag::FD_CLOEXEC)));
    }

    if flags.contains(OFlag::O_NONBLOCK) {
        res = res
            .and_then(|_| fcntl(pipe.0, FcntlArg::F_SETFL(OFlag::O_NONBLOCK)))
            .and_then(|_| fcntl(pipe.1, FcntlArg::F_SETFL(OFlag::O_NONBLOCK)));
    }

    match res {
        Ok(_) => Ok(pipe),
        Err(e) => {
            let _ = unistd::close(pipe.0);
            let _ = unistd::close(pipe.1);
            Err(e)
        }
    }
}

#[inline]
#[cfg(not(any(target_os = "ios", target_os = "macos")))]
fn pipe2(flags: nix::fcntl::OFlag) -> nix::Result<(RawFd, RawFd)> {
    unistd::pipe2(flags)
}

/// Register os signal handler.
///
/// Must be called before calling [`block_ctrl_c()`](fn.block_ctrl_c.html)
/// and should only be called once.
///
/// # Errors
/// Will return an error if a system error occurred.
///
#[inline]
pub unsafe fn init_os_handler() -> Result<impl Future<Output=Result<(), CtrlcError>>, Error>
{
    use nix::fcntl;
    use nix::sys::signal;

    PIPE = pipe2(fcntl::OFlag::O_CLOEXEC)?;

    let close_pipe = |e: nix::Error| -> Error {
        // Try to close the pipes. close() should not fail,
        // but if it does, there isn't much we can do
        let _ = unistd::close(PIPE.1);
        let _ = unistd::close(PIPE.0);
        e
    };

    // Make sure we never block on write in the os handler.
    if let Err(e) = fcntl::fcntl(PIPE.1, fcntl::FcntlArg::F_SETFL(fcntl::OFlag::O_NONBLOCK)) {
        return Err(close_pipe(e));
    }

    let handler = signal::SigHandler::Handler(os_handler);
    let new_action = signal::SigAction::new(
        handler,
        signal::SaFlags::SA_RESTART,
        signal::SigSet::empty(),
    );

    #[allow(unused_variables)]
    let sigint_old = match signal::sigaction(signal::Signal::SIGINT, &new_action) {
        Ok(old) => old,
        Err(e) => return Err(close_pipe(e)),
    };

    #[cfg(feature = "termination")]
    {
        let sigterm_old = match signal::sigaction(signal::Signal::SIGTERM, &new_action) {
            Ok(old) => old,
            Err(e) => {
                signal::sigaction(signal::Signal::SIGINT, &sigint_old).unwrap();
                return Err(close_pipe(e));
            }
        };
        match signal::sigaction(signal::Signal::SIGHUP, &new_action) {
            Ok(_) => {}
            Err(e) => {
                signal::sigaction(signal::Signal::SIGINT, &sigint_old).unwrap();
                signal::sigaction(signal::Signal::SIGTERM, &sigterm_old).unwrap();
                return Err(close_pipe(e));
            }
        }
    }

    Ok(
        async move {
            use std::io;
            use nix::sys::aio::AioCb;
            use nix::sys::aio::LioOpcode;
            use nix::sys::signal::SigevNotify;
            let mut buf = [0u8];

            // TODO: Can we safely convert the pipe fd into a std::io::Read
            // with std::os::unix::io::FromRawFd, this would handle EINTR
            // and everything for us.
            loop {
                let mut aio = AioCb::from_mut_slice( PIPE.0, 0, &mut buf[..], 0, SigevNotify::SigevNone, LioOpcode::LIO_NOP);
                aio.read()?;
                while aio.error() == Err(nix::errno::Errno::EINPROGRESS) {
                    #[cfg(feature = "tokio")]
                    tokio::time::sleep(std::time::Duration::from_millis(10)).await;
                    #[cfg(not(feature = "tokio"))]
                    std::thread::sleep(std::time::Duration::from_millis(10));
                }
                match aio.aio_return() {
                    Ok(1) => break,
                    Ok(_) => {
                        return Err(CtrlcError::System(io::ErrorKind::UnexpectedEof.into()))
                    },
                    Err(nix::errno::Errno::EINTR) => {}
                    Err(e) => return Err(e.into()),
                }
            }
            Ok(())
        }
    )
}