#!/bin/bash

# transset in a bash script
# Copyright (c) 2011-2012, Christopher Jeffrey

# Usage:
# by window id
#   settrans -w "$WINDOWID" -o 75
# by name
#   settrans -n "urxvt" -o 75
# by current window
#   settrans -c -o 75
# by selection
#   settrans -s -o 75
# increment current window 5%
#   settrans -c -o +5

# "command" is a shell built-in, faster than "which"
if test -z "$(command -v xprop)" -o -z "$(command -v xwininfo)"; then
  echo "Please install x11-utils/xorg-xprop/xorg-xwininfo." >& 2
  exit 1
fi

window=
opacity=
cur=
i=

# Read options
while getopts "scn:w:o:" option; do
  case "$option" in
    s) wprefix=''; window='' ;;
    c)
      active=$(xprop -root -notype "_NET_ACTIVE_WINDOW" \
        | sed 's/^.*\(0x\S*\).*$/\1/')
      wprefix='-id '; window="$active"
    ;;
    n) wprefix='-name '; window="$OPTARG" ;;
    w) wprefix='-id '; window="$OPTARG" ;;
    o) opacity="$OPTARG" ;;
    \?) exit 1;;
  esac
done

# Read positional arguments
shift $(($OPTIND - 1))
[ -n "$1" ] && opacity="$1"

# Validate opacity value
if [ -z "$opacity" ]; then
	echo "No opacity specified."
	exit 1
fi

opacity="$(echo "$opacity" \
	| sed -rn 's/^[[:space:]]*([+-]?[[:digit:]]+)[[:space:]]*$/\1/p')"

if [ -z "$opacity" ]; then
	echo "Invalid opacity value."
	exit 1
fi

# Get ID of the target window
if [ -z "$wprefix" ]; then
	treeout=$(xwininfo -children -frame)
else
	treeout=$(xwininfo -children $wprefix"$window")
fi

wid=$(echo "$treeout" | sed -n 's/^xwininfo:.*: \(0x[[:xdigit:]]*\).*$/\1/p')

if [ -z "$wid" ]; then
	echo "Failed to find window."
	exit 1
fi

# Make sure it's not root window
if echo "$treeout" | fgrep "Parent window id: 0x0" > /dev/null; then
	echo "Cannot set opacity on root window."
	exit 1
fi

# If it's already the topmost window
if echo "$treeout" | grep "Parent window id: 0x[[:xdigit:]]* (the root window)" > /dev/null; then
	topmost="$wid"
else
	# Get the whole window tree
	treeout="$(xwininfo -root -tree)"

	if [ -z "$treeout" ]; then
		echo "Failed to get root window tree."
		exit 1
	fi

	# Find the line number of the target window in the window tree
	lineno="$(echo -n "$treeout" | grep -nw "$wid" | head -n1 | cut -d ':' -f 1)"

	if [ -z "$lineno" ]; then
		echo "Failed to find window in window tree."
		exit 1
	fi

	# Find the highest ancestor of the target window below
	topmost=$(echo -n "$treeout" | head -n $(($lineno + 1)) | sed -n 's/^     \(0x[[:xdigit:]]*\).*/\1/p' | tail -n1)
fi

if [ -z "$topmost" ]; then
	echo "Failed to find the highest parent window below root of the" \
		"selected window."
	exit 1
fi

# Calculate the desired opacity
if echo "$opacity" | grep '^[+-]' > /dev/null; then
	sign=$(echo "$opacity" | cut -b1)
	cur=$(xprop -id "$topmost" -notype "_NET_WM_WINDOW_OPACITY" \
		| sed 's/^.*\b\([0-9]\+\).*$\|^.*$/\1/')
	[ -z "$cur" ] && cur=0xffffffff
	cur=$((cur * 100 / 0xffffffff))
	opacity="$(echo "$opacity" | sed 's/^[+-]//')"
  	opacity=$(($cur $sign $opacity))
fi

[ $opacity -lt 0 ] && opacity=0
[ $opacity -gt 100 ] && opacity=100

# Set opacity
opacity=$(($opacity * 0xffffffff / 100))
xprop -id "$topmost" -f _NET_WM_WINDOW_OPACITY 32c \
	-set _NET_WM_WINDOW_OPACITY "$opacity"