#!/usr/bin/env bash
# Herbstluftwm: Refocus the last-focused window

herbstclient \
  chain \
    `# quit existing instances of loop below` \
    , emit_hook quit_focuslastwindow \
    `# if the key is pressed` \
    , keybind Alt-Tab \
        `# read the content of the my_lastwin attribute` \
        substitute LASTWIN my_lastwin \
            `# and jump there` \
            jumpto LASTWIN \
    `# create necessary attributes, but do not fail if they already exist` \
    , silent try new_attr string my_lastwin \
    , silent try new_attr string my_curwin \
    `# fill them with the current window id` \
    , and ,, silent attr clients.focus \
          ,, substitute WIN clients.focus.winid set_attr my_curwin WIN \
          ,, substitute WIN clients.focus.winid set_attr my_lastwin WIN \

herbstclient -i '(focus_changed|reload|quit_focuslastwindow)' | \
    while read -r h winid t; do
        case "$h" in
            focus_changed)
                # never feed an 'unfocused' state into the queue
                # if a window is focused, shift the content of my_curwin into
                # my_lastwin. Note that we use $winid here and not the content
                # of clients.focus.winid in order to avoid race conditions.
                [[ "$winid" != "0x0" ]] && \
                herbstclient and \
                    , substitute WIN my_curwin set_attr my_lastwin WIN \
                    , set_attr my_curwin "$winid"
                ;;
            *)  # on any other hook, quit this loop. Note that the idling
                # herbstclient still lives until the next time a hook arrives
                # and then quits because it can not write to stdout anymore
                break ;;
        esac
    done