#!/usr/bin/env bash

set -eu

DIR="$(cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd)"
TINCRC="$DIR/tincrc"
MAC_ADDRESS=""

if [ -f "$TINCRC" ]; then
  source "$TINCRC"
else
  export MAC_ADDRESS=""
fi

if [[ -n "$MAC_ADDRESS" ]]; then
  echo "Skip generating MAC: MAC_ADDRESS with value '$MAC_ADDRESS' already defined in '$TINCRC'."
  exit 1
else
  # Locally Administered Address Ranges:
  #x2-xx-xx-xx-xx-xx
  #x6-xx-xx-xx-xx-xx
  #xA-xx-xx-xx-xx-xx
  #xE-xx-xx-xx-xx-xx
  # Replacing x with any hex value.
  printf 'export MAC_ADDRESS=02:1F:%02X:%02X:%02X:%02X\n' \
    $[RANDOM%256] $[RANDOM%256] $[RANDOM%256] $[RANDOM%256] \
    | tee -a "$TINCRC"
fi