#!/bin/sh

# Check darkness by computing luminance of the current terminal.
# see https://en.wikipedia.org/wiki/Luma_(video)

trap "stty $(stty -g)" EXIT
stty raw -echo min 0 time 0
printf '\e]11;?\e\\'
sleep 0.01

awk -v FS='' -v hex=123456789abcdef '{
	r = (16 * index(hex, $10) + index(hex, $11)) / 255
	g = (16 * index(hex, $15) + index(hex, $16)) / 255
	b = (16 * index(hex, $20) + index(hex, $21)) / 255
	exit (0.3 * r + 0.6 * g + 0.1 * b > 0.5)
}'