package inotify

import (
	"errors"

	"golang.org/x/sys/unix"
)

type poller struct {
	fd   int
	epfd int
}

func newPoller(fd int) (*poller, error) {
	var err error

	p := &poller{fd: -1, epfd: -1}
	p.fd = fd
	p.epfd, err = unix.EpollCreate1(unix.EPOLL_CLOEXEC)
	if err != nil {
		return nil, err
	}

	event := unix.EpollEvent{
		Fd:     int32(p.fd),
		Events: unix.EPOLLIN | unix.EPOLLET | unix.EPOLLERR | unix.EPOLLHUP,
	}
	err = unix.EpollCtl(p.epfd, unix.EPOLL_CTL_ADD, p.fd, &event)
	if err != nil {
		return nil, err
	}

	return p, nil
}

func (p *poller) wait() (bool, error) {
	for {
		events := make([]unix.EpollEvent, 1)

		n, err := unix.EpollWait(p.epfd, events, -1)
		if err != nil {
			if err == unix.EINTR {
				continue
			}
			return false, err
		}

		if n == 0 {
			continue
		}

		event := events[0]
		if event.Events&unix.EPOLLHUP != 0 {
			return false, errors.New("epoll hup")
		}
		if event.Events&unix.EPOLLERR != 0 {
			return false, errors.New("epoll error")
		}
		if event.Events&unix.EPOLLIN != 0 {
			return true, nil
		}
		return false, errors.New("unkown epoll event")
	}
}

func (p *poller) close() {
	if p.fd != -1 {
		unix.Close(p.fd)
	}
	if p.epfd != -1 {
		unix.Close(p.epfd)
	}
}