app "roctorrent"
    packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.5.0/Cufzl36_SnJ4QbOoEmiJ5dIpUxBvdB3NEySvuH82Wio.tar.br" }
    imports [pf.Stdout]
    provides [main] to pf


bDecodeStr: List U8 -> Result (List U8) [Malformatted]
bDecodeStr = \i ->
  when (List.splitFirst i ':') is
    Ok {before, after} -> 
      when (Str.fromUtf8 before) is 
      Ok ls -> 
        when (Str.toU32 ls) is
        Ok l -> 
          if Num.toU32 (List.len after) == l then 
            Ok after
          else 
            Err Malformatted
        Err _err -> Err Malformatted
      Err _err -> Err Malformatted
    Err _err -> Err Malformatted

expect 
  res = bDecodeStr (Str.toUtf8 "3:foo")
  res == Ok (Str.toUtf8 "foo")

expect 
  errCases = ["foo", "1:foo", "4:foo", ":", "foo:", "1:", "::"]
  List.all errCases \t -> 
    res = bDecodeStr (Str.toUtf8 t)
    res == Err Malformatted

main = 
  Stdout.line "Hello, World"