#!/bin/bash

filesexist() {
  ls $1 | grep .$2\$ | wc -l
}

anyexist() {
  [ `filesexist $1 $2` -gt 0 ]
}

replaygain() {
  if anyexist "$1" mp3
  then
    mp3gain -p -a -k -s i -o "$1"/*.mp3
  fi

  if anyexist "$1" flac
  then
    metaflac --add-replay-gain "$1"/*.flac
  fi
}

find -type d -newermt '-1 month' -exec replaygain {} \;