#!/bin/dash

[ "$(id -u)" = "0" ] && echo "This script should not be run as root" >&2 && exit 1

find . -depth \( -path '*/.*' -o -path '*/.*/*' \) -prune -o \( -type f -o -type d \) -print0 | xargs -0 -P 0 -I {} dash -c '

base="${1##*/}"
path="${1%/*}"

pattern="s/[^a-zA-Z0-9 ._-]//g; s/[ .-]/_/g; s/_+/_/g; s/^_+//; s/_+$//; s/[A-Z]/\L&/g"

[ -f "$1" ] && pattern="$pattern; s/_([^_]+)$/.\\1/"

new_name="$(echo "$base" | sed -E "$pattern")"

[ "$base" != "$new_name" ] && [ -e "$path/$new_name" ] && new_name="${$}_${new_name}"
[ "$base" != "$new_name" ] && mv "$1" "$path/$new_name"
' _ {}