% @doc
% porcelain wfc ops
-module(wfc).

-export_type([
    sentence/0
]).

-export([
    test/0,
    to_sentence/1,
    rep/1,
    reps/1,
    reps/2,
    add/1,
    mul/1
]).


test() ->
    reptest("(*)"),
    reptest("(+)"),
    reptest("(+ a b)"),
    reptest("(+ a b (* a b))"),
    ok.

reptest(S) ->
    io:format("input: ~s~n", [S]),
    rep(S),
    io:format("~n", []).

-type sentence() :: wfc_sentence:sentence().

-spec to_sentence(term()) -> {ok, sentence()} | {error, string()}.

to_sentence(Ltr = {c, _})  -> wfc_sentence:from_ltr(Ltr);
to_sentence(Word = {w, _}) -> wfc_sentence:from_word(Word);
to_sentence({s, Words})    -> wfc_sentence:from_list(Words);
to_sentence(Bad)           -> {error, wfc_utils:str("wfc:to_sentence: cannot coerce to sentence: ~p", [Bad])}.


-spec rep(string()) -> ok.
% @doc read/eval/print

rep(String) ->
    case wfc_read:expr(String) of
        {ok, Expr, Rest} ->
            case  wfc_eval:eval(Expr) of
                {ok, Result, _NewContext} ->
                    io:format("result: ~s~n", [wfc_pp:eval_result(Result)]),
                    %io:format("context: ~tw~n", [NewContext]),
                    ok;
                    %{ok, Result, NewContext};
                {error, Msg}              -> io:format("~s~n", [Msg])
            end,
            io:format("rest: ~p~n", [Rest]);
        {error, Message} ->
            io:format("~s~n", [Message])
    end.


-spec reps(string()) -> ok.
% @doc read/eval/print loop

reps(String) ->
    reps(String, wfc_eval_context:default()).

reps(String, Ctx) ->
    %io:format("reps(~ts, ~tw)~n", [String, Ctx]),
    case wfc_read:expr(String) of
        {ok, Expr, Rest} ->
            %io:format("{ok, ~tw, ~ts}~n", [Expr, Rest]),
            case  wfc_eval:eval(Expr, Ctx) of
                {ok, Result, NewContext} ->
                    io:format("result: ~s~n", [wfc_pp:eval_result(Result)]),
                    io:format("context: ~tw~n", [NewContext]),
                    reps(Rest, NewContext);
                {error, Msg}              -> io:format("~s~n", [Msg])
            end,
            io:format("rest: ~p~n~n", [Rest]);
        {error, Message} ->
            io:format("~s~n", [Message])
    end.



-spec add([term()]) -> {ok, sentence()} | {error, string()}.

add([Arg | Rest]) ->
    case to_sentence(Arg) of
        {ok, S} ->
            case add(Rest) of
                {ok, S2} ->
                    io:format("S2 = ~p~n", [S2]),
                    {ok, wfc_sentence:add(S, S2)};
                Error    -> Error
            end;
        Error   -> Error
    end;
add([]) ->
    {ok, wfc_sentence:zero()}.


-spec mul([term()]) -> {ok, sentence()} | {error, string()}.

mul([Arg | Rest]) ->
    case to_sentence(Arg) of
        {ok, S} ->
            case mul(Rest) of
                {ok, S2} -> {ok, wfc_sentence:mul(S, S2)};
                Error    -> Error
            end;
        Error   -> Error
    end;
mul([]) ->
    {ok, wfc_sentence:one()}.


zero() -> wfc_sentence:zero().
one() -> wfc_sentence:one().