#!/bin/bash
pname="$(basename "$0")"

function usage(){
    printf "%s usage:\n\n" "$pname"
    printf "\t %s -h|--help\n" "$pname"
    printf "\t %s \$login \$newUID\n" "$pname"
    printf "\n"
}

user=
newuid=
for arg ; do
    case "$arg" in
    -h|--help)
        usage
        exit 0
        ;;
    -*)
        printf "%s error: invalid option: %s\n" "$pname" "$arg"
        usage
        exit 1
        ;;
    *)
        if [ -z "$user" ] ; then
            user="$arg"
        elif [ -z "$newuid" ] ; then
            newuid="$arg"
        else
            printf "%s error: too many arguments '%s'.\n" "$pname" "$arg"
            usage
            exit 1
        fi
    esac
done

if [ -z "$newuid" ] ; then
    printf "%s error: missing argument.\n" "$pname"
    usage
    exit 1
fi

olduid="$(dscl . -read "/Users/$user" UniqueID|sed -e 's/UniqueID: //')"
if [ $olduid = $newuid ] ; then
    printf "%s error: User %s already has UID %d\n" "$pname" "$user" "$olduid"
    exit 1
fi

printf "Changeing UID.\n"
dscl . -change "/Users/$user" UniqueID $olduid $newuid
chguid="$(dscl . -read "/Users/$user" UniqueID|sed -e 's/UniqueID: //')"
if [ $chguid != $newuid ] ; then
    printf "%s error: Could not change %s's UID %d, it's still %d.\n" "$pname" "$user" "$chguid"
    exit 1
fi

printf "Changing ownership of files, will take some time…\n"
find -xP / -user $olduid -print0 | xargs -0 chown -h $newuid

printf "Renaming trash.\n"
mv /.Trashes/$olduid  /.Trashes/$newuid

printf "Renumbering complete.  -- It would be wise de reboot.\n"

exit 0