package main

import (
	"os"

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

// Delivers a value every time space is pressed. Puts the terminal in
// non-canonical mode so the keypress arrives without waiting for a newline,
// and returns a function that restores the original settings.
func watchSpace() (<-chan struct{}, func()) {
	ch := make(chan struct{}, 1)
	restore := func() {}
	fd := int(os.Stdin.Fd())

	if orig, err := unix.IoctlGetTermios(fd, unix.TCGETS); err == nil {
		saved := *orig
		raw := *orig
		raw.Lflag &^= unix.ICANON | unix.ECHO
		raw.Cc[unix.VMIN] = 1
		raw.Cc[unix.VTIME] = 0
		if unix.IoctlSetTermios(fd, unix.TCSETS, &raw) == nil {
			restore = func() { unix.IoctlSetTermios(fd, unix.TCSETS, &saved) }
		}
	}

	go func() {
		buf := make([]byte, 64)
		for {
			n, err := os.Stdin.Read(buf)
			if err != nil {
				return
			}
			for _, b := range buf[:n] {
				if b != ' ' {
					continue
				}
				select {
				case ch <- struct{}{}:
				default:
				}
			}
		}
	}()

	return ch, restore
}