pkgname=asus-screen-brightness
pkgver=1.0
pkgrel=1
pkgdesc="Helper for adjusting screen brightness in Asus Zenbook UX31A and similar models"
url="https://wiki.archlinux.org/index.php/ASUS_Zenbook_Prime_UX31A#Screen_backlight"
arch=('any')
license=(FDL1.3)
depends=('bash')
optdepends=('systemd: automatically grant user access to keyboard backlight control')

# general note: this package contains only two files; I don't see any added
# value in stuffing these into a tarball when I can also place them in here
# using heredocs (cf. http://stackoverflow.com/a/2954835/334761 for reference)
build() {
	mkdir -p $srcdir/$pkgname-$pkgver/
	cd $srcdir/$pkgname-$pkgver/
	# write the backlight helper script
	cat <<-'EOF' > ./asus-screen-brightness
		#!/bin/bash
		
		path="/sys/class/backlight/intel_backlight"
		
        # max should be 4296
        max=$(cat ${path}/max_brightness)
        
        step=$(($max/10))
        # for a value smaller than treshold, the steps are smaller for a more accurate setting at low in          tensity
        treshold=$((2*$step))
        previous=$(cat ${path}/brightness)
        
        function commit {
        	if [[ $1 = [0-9]* ]]
        	then 
        		if [[ $1 -gt $max ]]
        		then 
        			next=$max
        		elif [[ $1 -lt 0 ]]
        		then 
        			next=0
        		else 
        			next=$1
        		fi
        		echo $next >> ${path}/brightness
        		exit 0
        	else 
        		exit 1
        	fi
        }
        
        case "$1" in
         up)
        	if [[ $previous -le $treshold ]]
        	then 
        	    step=$(($step/4))
        	fi
        	commit $(($previous + $step))
           ;;
         down)
        	if [[ $previous -le $treshold ]]
        	then 
        	    step=$(($step/4))
        	fi
        	commit $(($previous - $step))
           ;;
         max)
        	 commit $max
           ;;
         off)
        	 commit 0
           ;;
         show)
        	 echo $previous
           ;;
         night)
        	 commit $(($max/4)) 
         	 ;;
         allowusers)
        	 # Allow members of users group to change brightness
        	 sudo chgrp users ${path}/brightness
        	 sudo chmod g+w ${path}/brightness
           ;;
         disallowusers)
        	 # Disallow members of users group to change brightness
        	 sudo chgrp root ${path}/brightness
        	 sudo chmod g-w ${path}/brightness
           ;;
         *)
        	 commit	$1
        esac
        
        exit 0		

	EOF
	# write the systemd unit file
	cat <<-'EOF' > ./asus-screen-brightness.service
		[Unit]
		Description=Allow user access to screen brightness
		After=systemd-udevd.service
		
		[Service]
		Type=oneshot
		RemainAfterExit=yes
		ExecStart=/usr/bin/asus-screen-brightness allowusers
		ExecStop=/usr/bin/asus-screen-brightness disallowusers
		
		[Install]
		WantedBy=multi-user.target
	EOF
}

package() {
	cd $srcdir/$pkgname-$pkgver/
	install -D -m 0755 asus-screen-brightness "$pkgdir/usr/bin/asus-screen-brightness"
	install -D -m 0644 asus-screen-brightness.service "$pkgdir/usr/lib/systemd/system/asus-screen-brightness.service"
}