#!/usr/bin/env bash

((NEW_NIX_FIRST_BUILD_UID=331))

id_available(){
	dscl . list /Users UniqueID | grep -E '\b'"$1"'\b' >/dev/null
}

change_nixbld_names_and_ids(){
	local name uid next_id
	((next_id=NEW_NIX_FIRST_BUILD_UID))
	echo "Attempting to migrate _nixbld users."
	echo "Each _nixbld# user should have its UID moved to $next_id+"
	while read -r name uid; do
		echo "   Checking $name (uid: $uid)"
		# iterate for a clean ID
		while id_available "$next_id"; do
			((next_id++))
			if ((next_id >= 400)); then
				echo "We've hit UID 400 without placing all of your users :("
				echo "You should use the commands in this script as a starting"
				echo "point to review your UID-space and manually move the"
				echo "remaining users (or delete them, if you don't need them)."
				exit 1
			fi
		done

		# first 2 are cleanup, it's OK if they aren't here
		sudo dscl . delete "/Users/$name" dsAttrTypeNative:_writers_passwd &>/dev/null || true
		sudo dscl . change "/Users/$name" NFSHomeDirectory "/private/var/empty 1" "/var/empty" &>/dev/null || true
		sudo dscl . change "/Users/$name" UniqueID "$uid" "$next_id"
		echo "      $name migrated to uid: $next_id"
	done < <(dscl . list /Users UniqueID | grep _nixbld | sort -n -k2)
}

change_nixbld_names_and_ids