rexen

-module(rexen@grammar).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([to_string/2, shunt/1]).
-export_type([operator_variant/1, token/0]).

-type operator_variant(EZK) :: o_paren |
    {asterix, EZK} |
    {plus, EZK} |
    {q_mark, EZK}.

-type token() :: c_paren |
    {letter, binary()} |
    {operator, operator_variant(integer())}.

-file("src/rexen/grammar.gleam", 17).
-spec tokenize(list(binary()), list(token())) -> list(token()).
tokenize(Input, Tokens) ->
    case Input of
        [] ->
            Tokens;

        [Char | Rest] ->
            Tok = case Char of
                <<"*"/utf8>> ->
                    {operator, {asterix, 3}};

                <<"?"/utf8>> ->
                    {operator, {q_mark, 2}};

                <<"+"/utf8>> ->
                    {operator, {plus, 1}};

                <<"("/utf8>> ->
                    {operator, o_paren};

                <<")"/utf8>> ->
                    c_paren;

                _ ->
                    {letter, Char}
            end,
            tokenize(Rest, lists:append(Tokens, [Tok]))
    end.

-file("src/rexen/grammar.gleam", 34).
-spec to_string(list(token()), binary()) -> binary().
to_string(Tokens, Output) ->
    case Tokens of
        [] ->
            Output;

        [Tok | Rest] ->
            case Tok of
                c_paren ->
                    to_string(Rest, gleam@string:append(Output, <<")"/utf8>>));

                {letter, Char} ->
                    to_string(Rest, gleam@string:append(Output, Char));

                {operator, Variant} ->
                    case Variant of
                        o_paren ->
                            to_string(
                                Rest,
                                gleam@string:append(Output, <<"("/utf8>>)
                            );

                        {asterix, _} ->
                            to_string(
                                Rest,
                                gleam@string:append(Output, <<"*"/utf8>>)
                            );

                        {plus, _} ->
                            to_string(
                                Rest,
                                gleam@string:append(Output, <<"+"/utf8>>)
                            );

                        {q_mark, _} ->
                            to_string(
                                Rest,
                                gleam@string:append(Output, <<"?"/utf8>>)
                            )
                    end
            end
    end.

-file("src/rexen/grammar.gleam", 99).
-spec emptystack(list(token()), list(operator_variant(integer()))) -> list(token()).
emptystack(Output, Stack) ->
    case Stack of
        [] ->
            Output;

        [Opvar | Rest] ->
            O = lists:append(Output, [{operator, Opvar}]),
            emptystack(O, Rest)
    end.

-file("src/rexen/grammar.gleam", 109).
-spec handle_operator(
    list(token()),
    list(operator_variant(integer())),
    operator_variant(integer()),
    integer()
) -> {list(token()), list(operator_variant(integer()))}.
handle_operator(Output, Stack, Variant, Precedence) ->
    case Stack of
        [] ->
            {Output, gleam@list:prepend(Stack, Variant)};

        [Opvar | Rest] ->
            case Opvar of
                o_paren ->
                    {Output, gleam@list:prepend(Stack, Variant)};

                {asterix, P} ->
                    case Precedence > P of
                        true ->
                            {Output, gleam@list:prepend(Stack, Variant)};

                        false ->
                            O = lists:append(Output, [{operator, Opvar}]),
                            handle_operator(O, Rest, Variant, Precedence)
                    end;

                {plus, P} ->
                    case Precedence > P of
                        true ->
                            {Output, gleam@list:prepend(Stack, Variant)};

                        false ->
                            O = lists:append(Output, [{operator, Opvar}]),
                            handle_operator(O, Rest, Variant, Precedence)
                    end;

                {q_mark, P} ->
                    case Precedence > P of
                        true ->
                            {Output, gleam@list:prepend(Stack, Variant)};

                        false ->
                            O = lists:append(Output, [{operator, Opvar}]),
                            handle_operator(O, Rest, Variant, Precedence)
                    end
            end
    end.

-file("src/rexen/grammar.gleam", 139).
-spec find_oparen(list(token()), list(operator_variant(integer()))) -> {ok,
        {list(token()), list(operator_variant(integer()))}} |
    {error, binary()}.
find_oparen(Output, Stack) ->
    case Stack of
        [] ->
            {error,
                <<"Trailing closing bracket found in the regular expression."/utf8>>};

        [Opval | Rest] ->
            case Opval of
                o_paren ->
                    {ok, {Output, Rest}};

                _ ->
                    Out = lists:append(Output, [{operator, Opval}]),
                    find_oparen(Out, Rest)
            end
    end.

-file("src/rexen/grammar.gleam", 65).
-spec shunt_loop(
    list(token()),
    list(token()),
    list(operator_variant(integer()))
) -> {ok, list(token())} | {error, binary()}.
shunt_loop(Input, Output, Stack) ->
    case Input of
        [] ->
            {ok, emptystack(Output, Stack)};

        [Tok | Rest] ->
            case Tok of
                {letter, _} ->
                    shunt_loop(Rest, lists:append(Output, [Tok]), Stack);

                c_paren ->
                    case find_oparen(Output, Stack) of
                        {ok, {O, S}} ->
                            shunt_loop(Rest, O, S);

                        {error, Err} ->
                            {error, Err}
                    end;

                {operator, Opvar} ->
                    case Opvar of
                        o_paren ->
                            shunt_loop(
                                Rest,
                                Output,
                                gleam@list:prepend(Stack, Opvar)
                            );

                        {asterix, P} ->
                            {O@1, S@1} = handle_operator(
                                Output,
                                Stack,
                                Opvar,
                                P
                            ),
                            shunt_loop(Rest, O@1, S@1);

                        {plus, P} ->
                            {O@1, S@1} = handle_operator(
                                Output,
                                Stack,
                                Opvar,
                                P
                            ),
                            shunt_loop(Rest, O@1, S@1);

                        {q_mark, P} ->
                            {O@1, S@1} = handle_operator(
                                Output,
                                Stack,
                                Opvar,
                                P
                            ),
                            shunt_loop(Rest, O@1, S@1)
                    end
            end
    end.

-file("src/rexen/grammar.gleam", 59).
-spec shunt(binary()) -> {ok, list(token())} | {error, binary()}.
shunt(Input) ->
    In = gleam@string:to_graphemes(Input),
    _pipe = tokenize(In, []),
    shunt_loop(_pipe, [], []).