%%%-------------------------------------------------------------------
%%% @copyright (C) 2018, Aeternity Anstalt
%%%-------------------------------------------------------------------

-module(enoise_protocol).

-export([ cipher/1
        , dh/1
        , from_name/1
        , hash/1
        , msgs/2
        , pattern/1
        , pre_msgs/2
        , to_name/1]).
-compile(export_all).
-type noise_pattern() :: nn | xk.
-type noise_msg()   :: {in | out, [enoise_hs_state:noise_token()]}.

-record(noise_protocol,
        { hs_pattern = noiseNN      :: noise_pattern()
        , dh         = dh25519      :: enoise_hs_state:noise_dh()
        , cipher     = 'ChaChaPoly' :: enoise_cipher_state:noise_cipher()
        , hash       = blake2b      :: enoise_sym_state:noise_hash()
        }).

-opaque protocol() :: #noise_protocol{}.

-export_type([noise_msg/0, noise_pattern/0, protocol/0]).

-spec cipher(Protocol :: protocol()) -> enoise_cipher_state:noise_cipher().
cipher(#noise_protocol{ cipher = Cipher }) ->
    Cipher.

-spec dh(Protocol :: protocol()) -> enoise_hs_state:noise_dh().
dh(#noise_protocol{ dh = Dh }) ->
    Dh.

-spec hash(Protocol :: protocol()) -> enoise_sym_state:noise_hash().
hash(#noise_protocol{ hash = Hash }) ->
    Hash.

-spec pattern(Protocol :: protocol()) -> noise_pattern().
pattern(#noise_protocol{ hs_pattern = Pattern }) ->
    Pattern.

-spec to_name(Protocol :: protocol()) -> binary().
to_name(Protocol = #noise_protocol{ hs_pattern = Pattern, dh = Dh
                                  , cipher = Cipher, hash = Hash }) ->
    case supported_pattern(Pattern) andalso supported_dh(Dh) andalso
        supported_cipher(Cipher) andalso supported_hash(Hash) of
        true  -> to_name(Pattern, Dh, Cipher, Hash);
        false -> error({protocol_not_recognized, Protocol})
    end.

-spec from_name(Name :: string() | binary()) -> protocol().
from_name(Bin) when is_binary(Bin) -> from_name(binary_to_list(Bin));
from_name(String) ->
    case string:lexemes(String, "_") of
        ["Noise", PatStr, DhStr, CipStr, HashStr] ->
            Pattern = from_name_pattern(PatStr),
            Dh      = from_name_dh(DhStr),
            Cipher  = from_name_cipher(CipStr),
            Hash    = from_name_hash(HashStr),
            case supported_pattern(Pattern) andalso supported_dh(Dh) andalso
                supported_cipher(Cipher) andalso supported_hash(Hash) of
                true  -> #noise_protocol{ hs_pattern = Pattern, dh = Dh
                                        , cipher = Cipher, hash = Hash };
                false -> error({name_not_recognized, String})
            end;
        _ ->
            error({name_not_recognized, String})
    end.

-spec msgs(Role :: enoise_hs_state:noise_role(), Protocol :: protocol()) -> [noise_msg()].
msgs(Role, #noise_protocol{ hs_pattern = Pattern }) ->
    {_Pre, Msgs} = protocol(Pattern),
    role_adapt(Role, Msgs).

-spec pre_msgs(Role :: enoise_hs_state:noise_role(), Protocol :: protocol()) -> [noise_msg()].
pre_msgs(Role, #noise_protocol{ hs_pattern = Pattern }) ->
    {PreMsgs, _Msgs} = protocol(Pattern),
    role_adapt(Role, PreMsgs).

role_adapt(initiator, Msgs) ->
    Msgs;
role_adapt(responder, Msgs) ->
    Flip = fun({in, Msg}) -> {out, Msg}; ({out, Msg}) -> {in, Msg} end,
    lists:map(Flip, Msgs).

protocol(nn) ->
    {[], [{out, [e]}, {in, [e, ee]}]};
protocol(kn) ->
    {[{out, [s]}], [{out, [e]}, {in, [e, ee, se]}]};
protocol(nk) ->
    {[{in, [s]}], [{out, [e, es]}, {in, [e, ee]}]};
protocol(kk) ->
    {[{out, [s]}, {in, [s]}], [{out, [e, es, ss]}, {in, [e, ee, se]}]};
protocol(nx) ->
    {[], [{out, [e]}, {in, [e, ee, s, es]}]};
protocol(kx) ->
    {[{out, [s]}], [{out, [e]}, {in, [e, ee, se, s, es]}]};
protocol(xn) ->
    {[], [{out, [e]}, {in, [e, ee]}, {out, [s, se]}]};
protocol(in) ->
    {[], [{out, [e, s]}, {in, [e, ee, se]}]};
protocol(xk) ->
    {[{in, [s]}], [{out, [e, es]}, {in, [e, ee]}, {out, [s, se]}]};
protocol(ik) ->
    {[{in, [s]}], [{out, [e, es, s, ss]}, {in, [e, ee, se]}]};
protocol(xx) ->
    {[], [{out, [e]}, {in, [e, ee, s, es]}, {out, [s, se]}]};
protocol(ix) ->
    {[], [{out, [e, s]}, {in, [e, ee, se, s, es]}]}.

supported_pattern(P) ->
    lists:member(P, [nn, kn, nk, kk, nx, kx, xn, in, xk, ik, xx, ix]).

supported_hash(Hash) ->
    lists:member(Hash, [blake2b, sha256, sha512]).

supported_cipher(Cipher) ->
    lists:member(Cipher, ['ChaChaPoly', 'AESGCM']).

supported_dh(Dh) ->
    lists:member(Dh, [dh25519]).

to_name(Pattern, Dh, Cipher, Hash) ->
    list_to_binary(lists:join("_", ["Noise", to_name_pattern(Pattern), to_name_dh(Dh),
                                    to_name_cipher(Cipher), to_name_hash(Hash)])).

to_name_pattern(Atom) ->
    [Simple | Rest] = string:lexemes(atom_to_list(Atom), "_"),
    string:uppercase(Simple) ++ lists:join("+", Rest).

from_name_pattern(String) ->
    [Init | Mod2] = string:lexemes(String, "+"),
    {Simple, Mod1} = lists:splitwith(fun(C) -> C >= $A andalso C =< $Z end, Init),
    list_to_atom(string:lowercase(Simple) ++
        case Mod1 of
            "" -> "";
            _  -> "_" ++ lists:join([Mod1 | Mod2], "_")
        end).

to_name_dh(dh25519) -> "25519";
to_name_dh(dh448)   -> "448".

from_name_dh(Dh) -> list_to_atom("dh" ++ Dh).

to_name_cipher(Cipher) -> atom_to_list(Cipher).

from_name_cipher(Cipher) -> list_to_atom(Cipher).

to_name_hash(sha256)  -> "SHA256";
to_name_hash(sha512)  -> "SHA512";
to_name_hash(blake2s) -> "BLAKE2s";
to_name_hash(blake2b) -> "BLAKE2b".

from_name_hash(Hash) -> list_to_atom(string:lowercase(Hash)).