#! /bin/bash

max() {
    if [[ "$1" -gt "$2" ]]; then echo "$1"; else echo "$2"; fi
}

min() {
    if [[ "$1" -lt "$2" ]]; then echo "$1"; else echo "$2"; fi
}

_get() {
    sudo ddcutil getvcp 10 | grep -o ' current value = \+[0-9]\+' | awk '{print $4}'
}

_set() {
    sudo ddcutil setvcp 10 "$1"
}

args="$*"

case "$args" in
    '') _get;;
    i | inc | increase) _set "$(min $(( $(_get) + 5)) 100)";;
    d | dec | decrease) _set "$(max $(( $(_get) - 5)) 0)";;
    *)
        if [[ "$args" =~ ^[0-9]+$ && "$args" -gt -1 && "$args" -lt 101 ]]; then
            _set "$args"
        else
            printf 'Error: expected a numeric argument between 0 and 100, but given "%s"\n' "$args" >&2
            exit 1
        fi
esac