-module (iban_server).
-compile(export_all).

-define(PERCENT, 37).  % $\%
-define(FULLSTOP, 46). % $\.
-define(IS_HEX(C), ((C >= $0 andalso C =< $9) orelse
    (C >= $a andalso C =< $f) orelse
    (C >= $A andalso C =< $F))).
-define(QS_SAFE(C), ((C >= $a andalso C =< $z) orelse
    (C >= $A andalso C =< $Z) orelse
    (C >= $0 andalso C =< $9) orelse
    (C =:= ?FULLSTOP orelse C =:= $- orelse C =:= $~ orelse
        C =:= $_))).

unhexdigit(C) when C >= $0, C =< $9 -> C - $0;
unhexdigit(C) when C >= $a, C =< $f -> C - $a + 10;
unhexdigit(C) when C >= $A, C =< $F -> C - $A + 10.

validate(SessID, Env, _Input) ->
    N = dict:fetch(query_string, dict:from_list(Env)),
    Output = io_lib:format("~p~n", [{unquote(N), iban:is_valid(unquote(N))}]),
    mod_esi:deliver(SessID, Output).

unquote(Binary) when is_binary(Binary) ->
    unquote(binary_to_list(Binary));
unquote(String) ->
    qs_revdecode(lists:reverse(String)).

qs_revdecode(S) ->
    qs_revdecode(S, []).

qs_revdecode([], Acc) ->
    Acc;
qs_revdecode([$+ | Rest], Acc) ->
    qs_revdecode(Rest, [$\s | Acc]);
qs_revdecode([Lo, Hi, ?PERCENT | Rest], Acc) when ?IS_HEX(Lo), ?IS_HEX(Hi) ->
    qs_revdecode(Rest, [(unhexdigit(Lo) bor (unhexdigit(Hi) bsl 4)) | Acc]);
qs_revdecode([C | Rest], Acc) ->
    qs_revdecode(Rest, [C | Acc]).