#! /bin/bash

error() {
    printf 'Error: %s\n' "$1" >&2
    exit 1
}

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

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

cmd="$1"
arg="$2"

case "$cmd" in
    '') _get;;
    get) _get;;
    set)
        case "$arg" in
            '') error 'expected a numeric argument between 0 and 100, given nothing!';;
            *)
                if [[ "$arg" =~ ^[0-9]+$ && "$arg" -gt -1 && "$arg" -lt 101 ]]; then
                    _set "$arg"
                else
                    error "expected a numeric argument between 0 and 100, but given '$arg'"
                fi
        esac;;
    *) error "unrecognized command: $cmd. Expect either get or set."
esac