#!/usr/bin/env bash

CACHE_FILE="/tmp/monitor-brightness-cache"
PID_FILE="/tmp/monitor-brightness-pid"
SCROLL_FILE="/tmp/monitor-brightness-scroll"
LOCK_FILE="/tmp/monitor-brightness-lock"

get_actual() {
    # Prevent concurrent ddcutil calls
    exec 9>"$LOCK_FILE"
    flock -n 9 || { cat "$CACHE_FILE" 2>/dev/null || echo "50"; return; }
    val=$(ddcutil getvcp 10 --display 1 2>/dev/null | grep -oP 'current value =\s*\K[0-9]+')
    exec 9>&-
    echo "$val"
}

# Initialize cache if missing
[ ! -f "$CACHE_FILE" ] && echo "50" > "$CACHE_FILE"

apply_brightness() {
    local value=$1
    [ -f "$PID_FILE" ] && kill "$(cat "$PID_FILE")" 2>/dev/null
    (
        echo $$ > "$PID_FILE"
        sleep 0.3
        exec 9>"$LOCK_FILE"
        flock 9
        ddcutil setvcp 10 "$value" --display 1 --noverify 2>/dev/null
        exec 9>&-
        rm -f "$PID_FILE"
    ) &
}

case "$1" in
    get)
        # If scrolled recently, use cache for instant feedback
        if [ -f "$SCROLL_FILE" ]; then
            age=$(( $(date +%s) - $(stat -c %Y "$SCROLL_FILE") ))
            if [ "$age" -lt 3 ]; then
                cat "$CACHE_FILE"
                exit 0
            fi
            rm -f "$SCROLL_FILE"
        fi
        # Otherwise fetch actual value
        val=$(get_actual)
        if [ -n "$val" ]; then
            echo "$val" > "$CACHE_FILE"
            echo "$val"
        else
            cat "$CACHE_FILE"
        fi
        ;;
    up)
        touch "$SCROLL_FILE"
        current=$(cat "$CACHE_FILE")
        new=$((current + 5))
        [ "$new" -gt 100 ] && new=100
        echo "$new" > "$CACHE_FILE"
        apply_brightness "$new"
        ;;
    down)
        touch "$SCROLL_FILE"
        current=$(cat "$CACHE_FILE")
        new=$((current - 5))
        [ "$new" -lt 0 ] && new=0
        echo "$new" > "$CACHE_FILE"
        apply_brightness "$new"
        ;;
esac