#!/bin/bash
# dim-warning start|stop: written by Wren Linux parts/swayidle.sh
# A warning before the screen turns off (it locks a minute after that). swayidle
# runs "start" 30 seconds before: the screen fades down slowly to 10% and a
# notification says so. Any key or mouse movement makes swayidle run "stop", which puts the
# brightness back exactly where it was. A screen with no backlight (a desktop
# monitor) can't be dimmed, so it only gets the notification.
#   WREN_DIM_SECONDS  how long the fade takes (default 30)
#   WREN_DIM_TO       the brightness it fades down to, in percent (default 10)
#   WREN_DIM_TICK     seconds between steps (default 1; a test makes it small)
STATE=${XDG_RUNTIME_DIR:-/tmp}/dim-warning
SECONDS_TOTAL=${WREN_DIM_SECONDS:-30}
TO=${WREN_DIM_TO:-10}
TICK=${WREN_DIM_TICK:-1}

backlight() { command -v brightnessctl >/dev/null && brightnessctl -m 2>/dev/null | grep -q .; }
percent() { brightnessctl -m | cut -d, -f4 | tr -d %; }

# stop: end the fade and put the brightness back
stop() {
    local pid
    pid=$(cat "$STATE.pid" 2>/dev/null)
    # (only a process that really is this script's fade, not a stale number)
    if [ -n "$pid" ] && { tr '\0' ' ' <"/proc/$pid/cmdline"; } 2>/dev/null | grep -q 'dim-warning'; then
        kill "$pid" 2>/dev/null
    fi
    if [ -f "$STATE.saved" ]; then
        brightnessctl -q set "$(cat "$STATE.saved")%" 2>/dev/null
    fi
    rm -f "$STATE.pid" "$STATE.saved"
}

fade() {
    local from=$1 steps i level
    steps=$((SECONDS_TOTAL))
    [ "$steps" -ge 1 ] || steps=1
    for ((i = 1; i <= steps; i++)); do
        sleep "$TICK"
        level=$((from - (from - TO) * i / steps))
        [ "$level" -ge "$TO" ] || level=$TO
        brightnessctl -q set "$level%" 2>/dev/null
    done
}

case ${1:-} in
    start)
        if command -v notify-send >/dev/null; then
            notify-send -a wren -u critical -t $((SECONDS_TOTAL * 1000)) \
                "Screen going dark" "Move the mouse or press a key to keep it on. It locks a minute after it goes dark." 2>/dev/null
        fi
        backlight || exit 0
        [ ! -f "$STATE.saved" ] || stop   # a fade still running from before: start over
        from=$(percent)
        # nothing to fade if it is already at or below the dim level
        [ "$from" -gt "$TO" ] || exit 0
        echo "$from" >"$STATE.saved"
        # the fade runs on its own, so swayidle is not kept waiting
        setsid bash "$0" fade "$from" >/dev/null 2>&1 &
        echo $! >"$STATE.pid"
        ;;
    fade) fade "$2" ;;
    stop) stop ;;
    *) echo "usage: dim-warning start|stop" >&2; exit 2 ;;
esac
exit 0