#!/usr/bin/bash
set -e

CUR="$(pactl get-sink-volume 0 | awk '$1 == "Volume:" {print substr($5, 1, length($5) - 1)}')"
SHIFT="${1}"

case "${1:0:1}" in
    "")
        exit 1
        ;;
    "+"|"-")
        NEW="$((CUR - CUR % SHIFT + SHIFT))"
        ;;
    *)
        NEW="$1"
        ;;
esac

[ "$NEW" -gt 100 ] && NEW=100

pactl set-sink-volume 0 "$NEW"%
pactl set-sink-mute 0 0

echo "$NEW"