// This information is in the file config/shortcuts.vdf, in binary format.
// It contains the non-Steam games with names, target (exe location) and
// tags/categories. To create a grid image we must compute the Steam ID, which
// is just crc32(target + label) + "02000000", using IEEE standard polynomials.
func addNonSteamGames(user User, games map[string]*Game) {
   shortcutsVdf := filepath.Join(user.Dir, "config", "shortcuts.vdf")
   if _, err := os.Stat(shortcutsVdf); err != nil {
      return
   }
   shortcutBytes, err := ioutil.ReadFile(shortcutsVdf)
   if err != nil {
      return
   }

   // The actual binary format is known, but using regexes is way easier than
   // parsing the entire file. If I run into any problems I'll replace this.
   gamePattern := regexp.MustCompile("(?i)appname\x00(.+?)\x00\x01exe\x00(.+?)\x00\x01.+?\x00tags\x00(.*?)\x08\x08")
   tagsPattern := regexp.MustCompile("\\d\x00(.+?)\x00")
   for _, gameGroups := range gamePattern.FindAllSubmatch(shortcutBytes, -1) {
      gameName := gameGroups[1]
      target := gameGroups[2]
      uniqueName := bytes.Join([][]byte{target, gameName}, []byte(""))
      // Does IEEE CRC32 of target concatenated with gameName, then convert
      // to 64bit Steam ID. No idea why Steam chose this operation.
      top := uint64(crc32.ChecksumIEEE(uniqueName)) | 0x80000000
      gameId := strconv.FormatUint(top<<32|0x02000000, 10)
      game := Game{gameId, string(gameName), []string{}, "", nil}
      games[gameId] = &game

      tagsText := gameGroups[3]
      for _, tagGroups := range tagsPattern.FindAllSubmatch(tagsText, -1) {
         tag := tagGroups[1]
         game.Tags = append(game.Tags, string(tag))
      }
   }
}