%%% @author Konstantin Rusalov
%%% @copyright (c) 2026 Konstantin Rusalov
-module(mtproxy_url).

-export([encode/1, encode/3, decode/1]).

-moduledoc """
MTProxy URL decoding and encoding
""".

-type ip4() :: {0..255, 0..255, 0..255, 0..255}.
-type ip6() :: {0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535, 0..65535}.
-type ip_port() :: 0..65535.

-type server() ::
    #{type := ip4, value := ip4()}
    | #{type := ip6, value := ip6()}
    | #{type := host, value := binary()}
    | binary().

-type secret() ::
    #{type := fake_tls, value := binary(), sni := binary()}
    | #{type := padding, value := binary()}
    | #{type := normal, value := binary()}
    | binary().

-type url() :: binary().

-doc """
Encode URL
## Examples:
```erlang
      Param = #{port => 443,server =>#{type => ip4,value => {1,1,1,1}}, secret => #{type => fake_tls,  value => <<1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16>>, sni => <<"google.com">>}},
      {ok,Result}=mtproxy_url:encode(Param).
```
""".
-spec encode(#{server := server(), port := ip_port(), secret := secret()}) -> {ok, binary()}.
encode(#{server := Server1, port := Port1, secret := Secret1}) ->
    encode(Server1, Port1, Secret1).
-spec encode(server(), ip_port(), secret()) -> {ok, binary()}.
encode(Server1, Port1, Secret1) ->
    Server =
        case Server1 of
            #{type := host, value := Host} -> Host;
            #{type := TypeIp, value := Ip} when TypeIp =:= ip4; TypeIp =:= ip6 -> inet:ntoa(Ip);
            Server1 when is_binary(Server1) -> Server1
        end,
    Secret =
        case Secret1 of
            #{type := fake_tls, value := Val, sni := Sni} ->
                binary:encode_hex(<<16#ee, Val/binary, Sni/binary>>, lowercase);
            #{type := padding, value := Val} ->
                binary:encode_hex(<<16#dd, Val/binary>>, lowercase);
            #{type := _, value := Val} ->
                binary:encode_hex(Val, lowercase);
            Secret1 when is_binary(Secret1) -> Secret1
        end,
    {ok,
        list_to_binary(
            io_lib:format("tg://proxy?server=~s&port=~p&secret=~s", [Server, Port1, Secret])
        )}.

-doc """
Decode URL
## Examples:
```erlang
      Param = <<"tg://proxy?server=1.1.1.1&port=443&secret=ee0102030405060708090a0b0c0d0e0f10676f6f676c652e636f6d">>,
      {ok,Result}=mtproxy_url:decode(Param).
```
""".
-spec decode(url()) ->
    {ok, #{server := server(), port := ip_port(), secret := secret()}}
    | {error, term()}
    | {term(), term()}.
decode(Url1) when is_binary(Url1) ->
    try
        Url = trim(Url1),
        Param = url_param(Url),
        case binary_to_integer(proplists:get_value(port, Param)) of
            Port when Port > 0 ->
                Server = server_decode(proplists:get_value(server, Param)),
                Secret = proplists:get_value(secret, Param),
                {ok, #{
                    server => Server,
                    port => Port,
                    secret => secret_decode(Secret)
                }};
            _ ->
                {error, port}
        end
    catch
        E:M -> {E, M}
    end.

-spec server_decode(binary()) -> server().
server_decode(Bin) ->
    server_decode_acc(Bin, []).

server_decode_acc(<<>>, Acc) ->
    H = list_to_binary(lists:reverse(Acc)),
    case inet:parse_address(binary_to_list(H)) of
        {error, einval} ->
            #{type => host, value => H};
        {ok, {_, _, _, _} = Ip} ->
            #{type => ip4, value => Ip};
        {ok, _ = Ip} ->
            #{type => ip6, value => Ip}
    end;
server_decode_acc(<<$.>>, Acc) ->
    server_decode_acc(<<>>, Acc);
server_decode_acc(<<H:8, T/binary>>, Acc) ->
    case H of
        H when H >= $A andalso H =< $Z ->
            server_decode_acc(T, [H + 32 | Acc]);
        H ->
            server_decode_acc(T, [H | Acc])
    end.

-spec secret_decode(binary()) -> secret().
secret_decode(Bin) ->
    Secret =
        try binary:decode_hex(Bin) of
            Hex ->
                case size(Hex) of
                    S when S < 16 ->
                        try base64_decode(Bin) of
                            X -> X
                        catch
                            _:_ -> Hex
                        end;
                    _S ->
                        Hex
                end
        catch
            _:_ -> base64_decode(Bin)
        end,
    secret_parse(Secret).

secret_parse(<<16#ee, Rand:16/binary, Bin/binary>>) ->
    #{type => fake_tls, value => Rand, sni => Bin};
secret_parse(<<16#dd, Rand:16/binary>>) ->
    #{type => padding, value => Rand};
secret_parse(<<Rand:16/binary>>) ->
    #{type => normal, value => Rand}.

-spec base64_decode(binary()) -> binary().
base64_decode(Bin) ->
    Bin1 = base64_normalize(Bin, 0, []),
    base64:decode(Bin1).
base64_normalize(<<>>, I, Acc) ->
    Padding =
        case I rem 4 of
            2 -> <<"==">>;
            3 -> <<"=">>;
            _ -> <<>>
        end,
    list_to_binary(lists:reverse([Padding | Acc]));
base64_normalize(<<$-, T/binary>>, I, Acc) ->
    base64_normalize(T, I + 1, [$+ | Acc]);
base64_normalize(<<$_, T/binary>>, I, Acc) ->
    base64_normalize(T, I + 1, [$/ | Acc]);
base64_normalize(<<H:8, T/binary>>, I, Acc) ->
    base64_normalize(T, I + 1, [H | Acc]).

url_query(<<$?, T/binary>>) -> T;
url_query(<<_:1/binary, T/binary>>) -> url_query(T);
url_query(<<>>) -> <<>>.

-spec url_param(binary()) -> [{atom(), binary()}].
url_param(Url) ->
    Query = url_query(Url),
    [
        begin
            case binary:split(X, [<<$=>>]) of
                [V, E] -> {param_to_atom(V), E};
                _ -> {undef, undef}
            end
        end
     || X <- binary:split(Query, [<<$&>>], [global]), X /= <<>>
    ].

param_to_atom(<<"server">>) -> server;
param_to_atom(<<"port">>) -> port;
param_to_atom(<<"secret">>) -> secret;
param_to_atom(_) -> undef.

-spec trim(binary()) -> binary().
trim(Bin) ->
    trim(Bin, []).
trim(<<>>, Acc) -> list_to_binary(lists:reverse(Acc));
trim(<<$\r, T/binary>>, Acc) -> trim(T, Acc);
trim(<<$\n, T/binary>>, Acc) -> trim(T, Acc);
trim(<<$\s, T/binary>>, Acc) -> trim(T, Acc);
trim(<<H:8, T/binary>>, Acc) -> trim(T, [H | Acc]).