-module(gurka_transform).
-export([parse_transform/2]).

parse_transform(Forms, _Options) ->
    forms(Forms).

forms([]) ->
    [];
forms([Form | Forms]) ->
    [form(Form) | forms(Forms)].

form({function, Line, Name, Arity, Clauses}) when Name =:= setup_feature; Name =:= setup_scenario; Name =:= given; Name =:= 'when'; Name =:= then ->
    function(Line, Name, Arity, Clauses);
form(Form) ->
    Form.

function(Line, Name, Arity, Clauses) ->
    {function, Line, Name, Arity, clauses(Clauses)}.

clauses([]) ->
    [];
clauses([Clause | Clauses]) ->
    [clause(Clause) | clauses(Clauses)].

clause({clause, ClauseLine, [{bin, _, [{bin_element, _, {string, StringLine, String}, default, default}]} | Head], Guard, Exprs}) ->
    {clause, ClauseLine, [process_string(StringLine, String) | Head], Guard, Exprs};

clause({clause, ClauseLine, [{string, StringLine, String} | Head], Guard, Exprs}) ->
    {clause, ClauseLine, [process_string(StringLine, String) | Head], Guard, Exprs};

clause({clause, ClauseLine, [{tuple, _, [{bin, _, [{bin_element, _, {string, StringLine, String}, default, default}]}, {cons, _, _, _}]} | Head], Guard, Exprs}) ->
    {clause, ClauseLine, [process_string(StringLine, String) | Head], Guard, Exprs};

clause({clause, ClauseLine, [{tuple, _, [{string, StringLine, String}, {cons, _, _, _}]} | Head], Guard, Exprs}) ->
    {clause, ClauseLine, [process_string(StringLine, String) | Head], Guard, Exprs};

clause({clause, Line, Head, Guard, Exprs}) ->
    {clause, Line, Head, Guard, Exprs};

clause(Clause) ->
    Clause.

process_string(Row, String) ->
    Tokens = gurka_parser:tokens(list_to_binary(String)),
    Pattern = build_pattern(Row, Tokens),
    {match, Row,
        {var, Row, 'Tokens'},
        Pattern}.

build_pattern(Row, []) ->
    {nil, Row};

build_pattern(Row, [<<$\$, Token/binary>> | Tokens]) ->
    Var = {var, Row, binary_to_atom(Token, utf8)},
    {cons, Row, Var, build_pattern(Row, Tokens)};

build_pattern(Row, [Token | Tokens]) ->
    Bin = {bin, Row, [{bin_element, Row, {string, Row, binary_to_list(Token)}, default, default}]},
    {cons, Row, Bin, build_pattern(Row, Tokens)}.