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use std::{io, os::unix::io::RawFd};

use super::{Interest, Mode, PollEvent, Readiness, Token};
use crate::no_nix_err;

use nix::sys::epoll;

pub struct Epoll {
    epoll_fd: RawFd,
}

fn make_flags(interest: Interest, mode: Mode) -> epoll::EpollFlags {
    let mut flags = match interest {
        Interest::Readable => epoll::EpollFlags::EPOLLIN,
        Interest::Writable => epoll::EpollFlags::EPOLLOUT,
        Interest::Both => epoll::EpollFlags::EPOLLIN | epoll::EpollFlags::EPOLLOUT,
    };
    match mode {
        Mode::Level => { /* This is the default */ }
        Mode::Edge => flags |= epoll::EpollFlags::EPOLLET,
        Mode::OneShot => flags |= epoll::EpollFlags::EPOLLONESHOT,
    }
    flags
}

fn flags_to_readiness(flags: epoll::EpollFlags) -> Readiness {
    Readiness {
        readable: flags.contains(epoll::EpollFlags::EPOLLIN),
        writable: flags.contains(epoll::EpollFlags::EPOLLOUT),
        error: flags.contains(epoll::EpollFlags::EPOLLERR),
    }
}

impl Epoll {
    pub(crate) fn new() -> io::Result<Epoll> {
        let epoll_fd =
            epoll::epoll_create1(epoll::EpollCreateFlags::EPOLL_CLOEXEC).map_err(no_nix_err)?;
        Ok(Epoll { epoll_fd })
    }

    pub(crate) fn poll(
        &mut self,
        timeout: Option<std::time::Duration>,
    ) -> io::Result<Vec<PollEvent>> {
        let mut buffer = [epoll::EpollEvent::empty(); 32];
        let timeout = timeout.map(|d| d.as_millis() as isize).unwrap_or(-1);
        let n_ready = epoll::epoll_wait(self.epoll_fd, &mut buffer, timeout).map_err(no_nix_err)?;
        let events = buffer
            .iter()
            .take(n_ready)
            .map(|event| PollEvent {
                readiness: flags_to_readiness(event.events()),
                token: Token::from_u64(event.data()),
            })
            .collect();
        Ok(events)
    }

    pub fn register(
        &mut self,
        fd: RawFd,
        interest: Interest,
        mode: Mode,
        token: Token,
    ) -> io::Result<()> {
        let mut event = epoll::EpollEvent::new(make_flags(interest, mode), token.to_u64());
        epoll::epoll_ctl(self.epoll_fd, epoll::EpollOp::EpollCtlAdd, fd, &mut event)
            .map_err(no_nix_err)
    }

    pub fn reregister(
        &mut self,
        fd: RawFd,
        interest: Interest,
        mode: Mode,
        token: Token,
    ) -> io::Result<()> {
        let mut event = epoll::EpollEvent::new(make_flags(interest, mode), token.to_u64());
        epoll::epoll_ctl(self.epoll_fd, epoll::EpollOp::EpollCtlMod, fd, &mut event)
            .map_err(no_nix_err)
    }

    pub fn unregister(&mut self, fd: RawFd) -> io::Result<()> {
        epoll::epoll_ctl(self.epoll_fd, epoll::EpollOp::EpollCtlDel, fd, None).map_err(no_nix_err)
    }
}

impl Drop for Epoll {
    fn drop(&mut self) {
        let _ = nix::unistd::close(self.epoll_fd);
    }
}