# Gets the id of the current focused window.
#
# Authors:
#   Alex Reece <awreece@gmail.com>
#

function focused_window_id {
  case "$OSTYPE" in
    (darwin*)
      osascript -e 'tell application "System Events" to ¬' \
                -e '  set focus_app_name to ¬' \
                -e '    name of first application process ¬' \
                -e '    whose frontmost is true' \
                -e 'tell application focus_app_name to ¬' \
                -e '  get id of front window'
      ;;
    (linux-gnu*)
      # http://stackoverflow.com/a/8688624/447288 
      xprop -root -f _NET_ACTIVE_WINDOW 0x ' $0' _NET_ACTIVE_WINDOW  \
        | awk '{print $2}'
      ;;
    (*)
      return 1
      ;;
  esac
}