#!/bin/sh
# SPDX-License-Identifier: MIT

#
# picom-trans
# Copyright (c) 2021, Subhaditya Nath
# Based on previous works of Christopher Jeffrey
#

#
# Conforming to POSIX-1.2007
# https://pubs.opengroup.org/onlinepubs/9699919799
#

# Usage:
#   $ picom-trans [options] [+|-]opacity
# By window id
#   $ picom-trans -w "$WINDOWID" 75
# By name
#   $ picom-trans -n "urxvt" 75
# By current window
#   $ picom-trans -c 75
# By selection
#   $ picom-trans 75
#   $ picom-trans -s 75
# Increment current window 5%
#   $ picom-trans -c +5
# Delete current window's opacity
#   $ picom-trans -c --delete
# Toggle current window's opacity between 90 and unset
#   $ picom-trans -c --toggle 90
# Reset all windows
#   $ picom-trans --reset


# Save $0 now to print correct value while printing from functions.
# Printing errormsgs from functions using "$0" prints the function name
# instead of the executable name.
EXE_NAME="$0"


# Instead of printing the full path to this file (e.g. /usr/bin/picom-trans)
# only print the base name (i.e. picom-trans)
EXE_NAME="$(basename "$EXE_NAME")"


print_usage()
{ #{{
  echo "Usage: $EXE_NAME [options] [+|-]opacity"
  echo ""
  echo "Options:"
  echo "  -h, --help                Print this help message."
  echo "  -o, --opacity OPACITY     Specify the new opacity value in range 0-100 for the window. If"
  echo "                            prefixed with + or -, increment or decrement from the current"
  echo "                            opacity of the target window."
  echo ""
  echo "Actions:"
  echo "  -g, --get                 Print current opacity of the target window."
  echo "  -d, --delete              Delete opacity of the target window."
  echo "  -t, --toggle              Toggle the target window's opacity, i.e. set if not already set"
  echo "                            and delete else."
  echo "  -r, --reset               Reset opacity for all windows."
  echo ""
  echo "Window Selection:"
  echo "  -s, --select              Select target window with mouse cursor. (DEFAULT)"
  echo "  -c, --current             Select the currently active window as target."
  echo "  -n, --name WINDOW_NAME    Specify and try to match a window name."
  echo "  -w, --window WINDOW_ID    Specify the window id of the target window."
} #}}


parse_args()
{ #{{
  i=1       # because we start from "$1", not from "$0"
  while [ $i -le $# ]
  do
    #### [START] Convert GNU longopts to POSIX equivalents ####
    if [ "$1" = "--${1##--}" ]  # check if $1 is a longopt
    then
      # Catch invalid options
      case "$1" in
        (--opacity=|--name=|--window=)
          echo "$EXE_NAME: option ${1%=} needs a value" >&2
          exit 1;;
        (--opacity|--name|--window)
          test $i -eq $# \
            && echo "$EXE_NAME: option $1 needs a value" >&2 \
            && exit 1;;
      esac

      # Separate  "--ARG=VAL"  into  "--ARG" "VAL"
      case "$1" in
        (--opacity=*|--name=*|--window=*)
          ARG="$(echo "$1" | sed -E 's/(--[^=]+)=.*$/\1/')"
          VAL="${1##${ARG}=}"
          shift && set -- "$ARG" "$VAL" "$@"
      esac

      # Turn into short form
      case "$1" in
        (--help|--opacity|--get|--delete|--toggle|--reset|--select|--current|--name|--window)
          ARG=${1#-}                          # remove one '-' from prefix
          ARG="$(echo "$ARG" | cut -c -2)"    # get first two characters
          shift && set -- "$ARG" "$@"
      esac

      # If the argument still starts with --, it is an invalid argument
      case "$1" in
        (--*)
          echo "$EXE_NAME: illegal option $1" >&2
          exit 1
      esac
    fi
    #### [END] Convert GNU longopts to POSIX equivalents ####


    #### [START] Prepend '-o' to  standalone opacity values ####
    # Iterate over every argument and check if it is an opacity without the -o
    # option in the previous argument. If so, then prepend the -o option.
    # e.g. Turn this -
    #     picom-trans -c +10 -s
    # into this -
    #     picom-trans -c -o +10 -s
    #
    # NOTE: Don't touch arguments that are preceded by -o, -w, or -n (i.e. the
    # options that take a value.)
    # e.g. This -
    #     picom-trans -w 75 -o 90
    # should NOT be turned into this -
    #     picom-trans -w -o 75 -o 90
    # We ensure this by checking the "$#"th (i.e. the last) argument. If
    # argument is an option that needs a value, we don't do anything to $1.
    #
    # NOTE: we are using printf because most echo implementations aren't
    # POSIX-compliant. For example, according to POSIX.1-2017, echo doesn't
    # support any options, so,
    #   $ echo "-n"
    # should output -
    #   -n
    # But it doesn't. It instead interprets the "-n" as the option -n, which,
    # in most implementations, means that the trailing newline should not be
    # printed.
    if echo "$1" | grep -qE '^[+-]?[[:digit:]]+%?$' && \
      ! eval "printf '%s' \"\${$#}\"" | grep -q '^-[hdtrgsc]*[own]$'
    # NOTE: eval "printf '%s' \"\${$#}\""  means 'print the last argument'
    # NOTE: The letters inside the first  square brackets (ie. hdtrgsc) are
    #       the same as those in the getopts argument, minus those that are
    #       followed by a ':'
    # NOTE: The letters inside the second square brackets (ie. own) are
    #       the same as those in the getopts argument, minus those that are
    #       NOT followed by a ':'
    then
      set -- "$@" "-o"
      i=$(( i + 1 ))
    fi
    #### [END] Prepend '-o' to  standalone opacity values ####


    # Prepare for next iteration
    ARG="$1"
    shift && set -- "$@" "$ARG"
    i=$(( i + 1 ))
  done


  # NOTE: DO NOT ATTEMPT TO USE "$OPTIND" INSIDE THE getopts LOOP
  # - https://github.com/yshui/picom/pull/634#discussion_r654571535
  # - https://www.mail-archive.com/austin-group-l%40opengroup.org/msg04112.html
  OPTIND=1
  while getopts 'ho:dtrgsn:w:c' OPTION
  do
    case "$OPTION" in
      (h) print_usage; exit 0;;
      (o) target_opacity="$OPTARG";;
      (d) action=delete;;
      (t) action=toggle;;
      (r) action=reset;;
      (g) action=get;;
      (s) winidtype=;         winid=;;
      (n) winidtype=-name;    winid="$OPTARG";;
      (w) winidtype=-id;      winid="$OPTARG";;
      (c) winidtype=-id;      winid="$(get_focused_window_id)";;
      (\?) exit 1
    esac
  done
} #}}


get_target_window_id()
{ #{{

  # Get the output of xwininfo
  if test -z "$winidtype"
  then xwininfo_output="$(xwininfo -children -frame)"
  elif test "$winidtype" = "-name"
  then xwininfo_output="$(xwininfo -children -name "$winid")"
  elif test "$winidtype" = "-id"
  then
    # First, check if supplied window id is valid
    if ! echo "$winid" | grep -Eiq '^[[:space:]]*(0x[[:xdigit:]]+|[[:digit:]]+)[[:space:]]*$'
    then
      echo "Bad window ID" >&2
      exit 1
    fi
    xwininfo_output="$(xwininfo -children -id "$winid")"
  fi

  # Extract window id from xwininfo output
  winid="$(echo "$xwininfo_output" | sed -n 's/^xwininfo:.*: \(0x[[:xdigit:]]*\).*$/\1/p')"
  if test -z "$winid"
  then
    echo "Failed to find window" >&2
    exit 1
  fi

  # Make sure it's not root window
  if echo "$xwininfo_output" | grep -Fq "Parent window id: 0x0"
  then
    echo "Cannot set opacity on root window" >&2
    exit 1
  fi

  # If it's not the topmost window, get the topmost window
  if ! echo "$xwininfo_output" | grep -q 'Parent window id: 0x[[:xdigit:]]* (the root window)'
  then
    window_tree="$(xwininfo -root -tree)"
    if test -z "$window_tree"
    then
      echo "Failed to get root window tree" >&2
      exit 1
    fi

    # Find the highest ancestor of the target window
    winid="$(echo "$window_tree" \
      | sed -n "/^\s*$winid/q;s/^     \(0x[[:xdigit:]]*\).*/\1/p" \
      | tail -n 1)"
    if test -z "$winid"
    then
      echo "Failed to find window in window tree" >&2
      exit 1
    fi
  fi
  if test -z "$winid"
  then
    echo "Failed to find the highest parent window below root of the selected window" >&2
    exit 1
  fi

  echo "$winid"
} #}}

get_focused_window_id()
{ #{{
  id="$(xprop -root -notype -f _NET_ACTIVE_WINDOW 32x '$0' _NET_ACTIVE_WINDOW)"
  echo "${id#_NET_ACTIVE_WINDOW}"
} #}}

get_current_opacity()
{ #{{
  # Gets current opacity in the range 0-100
  # Doesn't output anything if opacity isn't set
  cur="$(xprop -id "$winid" -notype -f _NET_WM_WINDOW_OPACITY 32c '$0' _NET_WM_WINDOW_OPACITY)"
  cur="${cur#_NET_WM_WINDOW_OPACITY}"
  cur="${cur%:*}"
  test -n "$cur" &&
    cur=$(( cur * 100 / 0xffffffff ))
  echo "$cur"
} #}}


get_opacity()
{ #{{
  cur="$(get_current_opacity)"
  test -z "$cur" && cur=100     # Unset opacity means fully opaque
  echo "$cur"
  exit 0
} #}}

delete_opacity()
{ #{{
  xprop -id "$winid" -remove _NET_WM_WINDOW_OPACITY
  exit 0
} #}}

reset_opacity()  # Reset opacity of all windows
{ #{{
  for winid in $(xwininfo -root -tree | sed -n 's/^     \(0x[[:xdigit:]]*\).*/\1/p')
  do xprop -id "$winid" -remove _NET_WM_WINDOW_OPACITY 2>/dev/null
  done
  exit 0
} #}}

set_opacity()
{ #{{
  if ! echo "$target_opacity" | grep -qE '^[+-]?[[:digit:]]+%?$'
  then
    if test -z "$target_opacity"
    then echo "No opacity specified" >&2
    else echo "Invalid opacity specified: $target_opacity" >&2
    fi
    exit 1
  fi

  # strip trailing '%' sign, if any
  target_opacity="${target_opacity%%%}"

  if echo "$target_opacity" | grep -q '^[+-]'
  then
    current_opacity="$(get_current_opacity)"
    test -z "$current_opacity" && current_opacity=100
    target_opacity=$(( current_opacity + target_opacity ))
  fi

  test $target_opacity -lt 0   && target_opacity=0
  test $target_opacity -gt 100 && target_opacity=100

  target_opacity=$(( target_opacity * 0xffffffff / 100 ))
  xprop -id "$winid" -f _NET_WM_WINDOW_OPACITY 32c \
      -set _NET_WM_WINDOW_OPACITY "$target_opacity"

  exit $?
} #}}

toggle_opacity()
{ #{{
  # If opacity is currently set, unset it.
  # If opacity is currently unset, set opacity to the supplied value. If no
  # value is supplied, we default to 100%.
  if test -z "$(get_current_opacity)"
  then
    test -n "$target_opacity" || target_opacity=100
    set_opacity
  else
    delete_opacity
  fi
} #}}


# Warn about rename of compton to picom
case "$0" in
  *compton-trans*)  echo "Warning: compton has been renamed, please use picom-trans instead" >&2;;
esac


# Check if both xwininfo and xprop are available
if ! command -v xprop >/dev/null || ! command -v xwininfo >/dev/null
then
  echo "The command xwininfo or xprop is not available. They might reside in a package named xwininfo, xprop, x11-utils, xorg-xprop, or xorg-xwininfo" >&2
  exit 1
fi


# No arguments given. Show help.
if test $# -eq 0
then
  print_usage >&2
  exit 1
fi


# Variables
#   action is set to 'set' by default
action=set
winid=
winidtype=
target_opacity=

# If there's only one argument, and it's a valid opacity
# then take it as target_opacity.  Else, parse all arguments.
if test $# -eq 1 && echo "$1" | grep -qE '^[+-]?[[:digit:]]+%?$'
then
  target_opacity=$1
  shift
else
  parse_args "$@"
fi


# reset_opacity doesn't need $winid
case $action in
  (reset)   reset_opacity;;
esac

# Any other action needs $winid
#
# NOTE: Do NOT change the order of winid= and winidtype= below
#       the output of get_target_window_id depends on $winidtype
#
# NOTE: If get_target_window_id returns with a non-zero $?
#       that must mean that some error occured. So, exit with that same $?
#
winid=$(get_target_window_id) || exit $?
winidtype=-id
case $action in
  (set)     set_opacity;;
  (get)     get_opacity;;
  (delete)  delete_opacity;;
  (toggle)  toggle_opacity;;
esac


# We should never reach this part of the file
echo "This sentence shouldn't have been printed. Please file a bug report." >&2
exit 128


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