use libc::{
    SA_RESTART, SA_SIGINFO, SIGCHLD, WNOHANG, c_int, sigaction, siginfo_t, sigset_t, waitpid,
};
use std::os::raw::c_void;

// extern "C" because:
// https://doc.rust-lang.org/reference/items/external-blocks.html?spm=a2ty_o01.29997173.0.0.63e251718NCvPc#abi
// Doc comments needed...
extern "C" fn sigchld_handler(_signal: c_int, _info: *mut siginfo_t, _context: *mut c_void) {
    let saved_errno = unsafe { *libc::__errno_location() };

    loop {
        let mut status: c_int = 0;
        let pid = unsafe { waitpid(-1, &mut status as *mut c_int, WNOHANG) };

        match pid {
            0 => break,
            -1 => {
                let errno = unsafe { *libc::__errno_location() };
                if errno == libc::ECHILD {
                    break;
                }
            }
            _ => { /* If it doesnt work, ill add the logging here */ }
        }
    }

    unsafe { *libc::__errno_location() = saved_errno };
}

pub fn setup_sigchld_handler() -> Result<(), Box<dyn std::error::Error>> {
    unsafe {
        let mut sigact: sigaction = std::mem::zeroed();

        sigact.sa_sigaction = sigchld_handler as *const () as usize;
        sigact.sa_flags = SA_RESTART | SA_SIGINFO;

        libc::sigemptyset(&mut sigact.sa_mask as *mut sigset_t);
        libc::sigaddset(&mut sigact.sa_mask as *mut sigset_t, SIGCHLD);

        if libc::sigaction(SIGCHLD, &sigact, std::ptr::null_mut()) == -1 {
            return Err("Failed to set SIGCHLD handler".into());
        }
    }
    Ok(())
}