lastcwd

#!/usr/bin/env bash

# shellcheck disable=SC2009

# Fail on errors.
set -eEo pipefail
shopt -s inherit_errexit >/dev/null 2>&1 || true

# Print foreground descendant pid for given pid, or 0.
foreground_pid() {
    local -ra pids=("$@")
    if [[ -n "${pids[*]}" ]]; then
        local -a tmp=() cpids=()
        local pid wid
        for pid in "${pids[@]}"; do
            if ps -o stat:1= "$pid"|grep -qFm1 +; then
                wid="$(ps e -o args= "$pid"|grep -o "WINDOWID=[0-9][0-9]*"|cut -d= -f2 || true)"
                if [[ -n "$wid" && "$wid" == "$((window_id))" ]]; then
                    echo "$pid"
                    return
                fi
            else
                read -ra tmp <<<"$(ps -o pid:1= --ppid "$pid"|tr '\n' '\t')"
                cpids+=("${tmp[@]}")
            fi
        done
        foreground_pid "${cpids[@]}"
    else
        echo 0
    fi
}

# Print cwd for pid.
pid_cwd() { pwdx "$1"|cut -d' ' -f2-; }

# Establish active window and its pid.
window_id="$(xprop -root 32x '\t$0' _NET_ACTIVE_WINDOW|cut -f2)"
window_pid="$(xprop _NET_WM_PID -id "$window_id"|cut -d' ' -f3)"

# Establish foreground pid. Don't bother if none of window_pid's children have a tty.
if ps -o tty= --ppid "$window_pid"|grep -qv '^?$'; then
    fgpid="$(foreground_pid "$window_pid")"
else
    fgpid=0
fi

# Print cwd for foreground process with special handling for tmux.
if [[ "$fgpid" -eq 0 ]]; then
    pid_cwd "$window_pid"
elif ps -o comm:1= "$fgpid"|grep -q '^tmux'; then
    client_name="$(tmux list-clients -F '#{client_name} #{client_pid}'|grep " $fgpid\$"|cut -d' ' -f1)"
    fgpid2="$(foreground_pid "$(tmux display-message -t "$client_name" -p '#{pane_pid}')")"
    pid_cwd "$fgpid2"
else
    pid_cwd "$fgpid"
fi