rest/src/rest.erl

-module(rest).
%%-author('Dmitry Bushmelev').

-export([behaviour_info/1, parse_transform/2, generate_to_json/3, binarize/1,
  generate_from_json/3, from_json/2, to_json/1, to_binary/1, parse/1, atomize/1]).


behaviour_info(callbacks) -> [{exists, 1}, {get, 0}, {get, 1}, {post, 1}, {delete, 1}, {from_json, 2}, {to_json, 1}];
behaviour_info(_) -> undefined.

parse_transform(Forms, _Options) ->
  %io:format("~p~n", [Forms]),
  RecordName = rest_record(Forms),
  RecordFields = record_fields(RecordName, Forms),
  Forms1 = generate({from_json, 2}, RecordName, RecordFields, Forms),
  Forms2 = generate({to_json, 1}, RecordName, RecordFields, Forms1),
  %io:format("~p~n", [Forms2]),
  Forms2.

rest_record([]) -> [];
rest_record([{attribute, _, rest_record, RecordName} | _Forms]) -> RecordName;
rest_record([_ | Forms]) -> rest_record(Forms).

record_field({record_field, _, {atom, _, Field}   }, _RecordName) ->
  %io:format("Case 1: ~p~n", [Field]),
  Field;
record_field({record_field, _, {atom, _, Field}, _Type}, _RecordName) ->
  %io:format("Case 2: ~p~n", [Field]),
  Field;
record_field({typed_record_field, {record_field, _, {atom, _, Field}, _}, Type}, RecordName) ->
  Rec = allow(Type),
  erlang:put({RecordName, Field}, Rec),
  %case Rec of
  %  undefined -> io:format("Case 3: ~p~n", [Field]);
  %          _ -> io:format("Case 3: ~p, Link: ~p~n", [Field, Rec])
  %end,
  Field.

allow({type, _, union, Components}) -> findType(Components);
allow(Type) -> findType([Type]).

findType([]) -> undefined;
findType([{type, _, record, [{atom, _, X}]}|_T]) -> X;
findType([{remote_type, _, [{atom, _, _}, {atom, _, X}, _]}|_T]) -> X;
findType([_H|T]) ->
  %io:format("Unknown Type: ~p~n", [_H]),
  findType(T).

record_fields(_RecordName, []) -> [];
record_fields(RecordName, [{attribute, _, record, {RecordName, Fields}} | _Forms]) ->
  [record_field(Field, RecordName) || Field <- Fields];
record_fields(RecordName, [_ | Forms]) -> record_fields(RecordName, Forms).

last_export_line(Exports) ->
  case lists:reverse(Exports) of
    [{_, Line, _, _} | _] -> Line;
    _ -> 0
  end.

generate({FunName, _Arity} = Fun, Record, Fields, Forms) ->
  Exports = lists:filter(
    fun({attribute, _, export, _}) -> true;
       (_) -> false
    end, Forms),
  case exported(Fun, Exports) of
    true  -> Forms;
    false ->
      Line = last_export_line(Exports),
      Gen = list_to_atom("generate_" ++ atom_to_list(FunName)),
      lists:flatten([?MODULE:Gen(export(Form, Fun, Line), Record, Fields) || Form <- Forms])
  end.

exported(Fun, Exports) ->
  lists:member(Fun, lists:flatten([E || {attribute, _, export, E} <- Exports])).

field_var(Field) -> erlang:list_to_atom("V_" ++ erlang:atom_to_list(Field)).

from_json_prelude(Line) ->
  {clause, Line,
   [{nil, Line}, {var, Line, 'Acc'}],
   [],
   [{var, Line, 'Acc'}]}.

from_json_coda(Line) ->
  {clause, Line,
   [{cons, Line, {var, Line, '_'}, {var, Line, 'Json'}}, {var, Line, 'Acc'}],
   [],
   [{call, Line, {atom, Line, from_json}, [
     %{var, Line, 'Json'}, % here is fix for recursive binarized preprocessing to raw X:from_json
     {call, Line, {remote, Line, {atom, Line, ?MODULE}, {atom, Line, binarize}}, [{var, Line, 'Json'}]},
     {var, Line, 'Acc'}
   ]}]}.

from_json_clauses(_, _, []) -> [];
from_json_clauses(Line, Record, [Field | Fields]) ->
  [{clause, Line,
    [{cons, Line,
      {tuple, Line,
       [{bin, Line,
         [{bin_element, Line, {string, Line, erlang:atom_to_list(Field)}, default, default}]},
        {var, Line, field_var(Field)}]},
      {var, Line, 'Json'}},
     {var, Line, 'Acc'}],
    [],
    [{call, Line,
      {atom, Line, from_json},
      [{var, Line, 'Json'},
       {record, Line,
        {var, Line, 'Acc'},
        Record,
        [{record_field, Line,
          {atom, Line, Field},
          {call, Line,
           {remote, Line, {atom, Line, ?MODULE }, {atom, Line, from_json}},
           [{var, Line, field_var(Field)},
            {atom, Line,
             case erlang:get({Record, Field}) of
               undefined -> Record;
               FieldType -> FieldType
             end}]}
          }]}]}]}
   | from_json_clauses(Line, Record, Fields)].

generate_from_json({eof, Line}, Record, Fields) ->
  [{function, Line, from_json, 2,
    [from_json_prelude(Line)] ++ from_json_clauses(Line, Record, Fields) ++ [from_json_coda(Line)]},
   {eof, Line + 1}];
generate_from_json(Form, _, _) -> Form.

export({attribute, LastExportLine, export, Exports}, Fun, LastExportLine) ->
  {attribute, LastExportLine, export, [Fun | Exports]};
export(Form, _, _) -> Form.

to_json_cons(Line, []) -> {nil, Line};
to_json_cons(Line, [Field | Fields]) ->
  {cons, Line,
   {tuple, Line,
    [{atom, Line, Field},
     {call, Line,
      {remote, Line, {atom, Line, ?MODULE}, {atom, Line, to_json}},
      [{var, Line, field_var(Field)}]}]},
   to_json_cons(Line, Fields)}.

generate_to_json({eof, Line}, Record, Fields) ->
  [{function, Line, to_json, 1,
    [{clause, Line,
      [{record, Line, Record,
        [{record_field, Line, {atom, Line, F}, {var, Line, field_var(F)}} || F <- Fields]}],
      [],
      [to_json_cons(Line, Fields)]}]},
   {eof, Line + 1}];

generate_to_json(Form, _, _) -> Form.

from_json(<<Data/binary>>, _) ->
  erlang:binary_to_list(Data);
from_json({struct, Props}, X) ->
  from_json(Props, X);
from_json([{Key, _}|_] = Props, X) when Key =/= struct ->
  X:from_json(binarize(Props), X:new());
from_json(Any, _X) -> Any.

atomize([{Key, _}|_]=Props) when Key =/= struct ->
  lists:map(fun ({K, V}) when erlang:is_atom(K)   -> {K, V};
                ({K, V}) when erlang:is_binary(K) -> {erlang:list_to_existing_atom(erlang:binary_to_list(K)), V} end, Props);
atomize(X) -> X.

binarize([{Key, _}|_]=Props) when Key =/= struct ->
  lists:map(fun ({K, V}) when erlang:is_atom(K)   -> {erlang:list_to_binary(erlang:atom_to_list(K)), allowed_value(V)};
                ({K, V}) when erlang:is_binary(K) -> {K, allowed_value(V)} end, Props);
binarize(X) -> X.

allowed_value(X) when erlang:is_reference(X) -> [];
allowed_value(X) -> X.

to_json(X) when erlang:is_tuple(X) ->
  Module = erlang:hd(erlang:tuple_to_list(X)),
  Module:to_json(X);
to_json(Data) ->
  case is_string(Data) of
    true  -> to_binary(Data);
    false -> json_match(Data)
  end.

json_match([{_, _} | _] = Props) ->
  [{to_binary(Key), to_json(Value)} || {Key, Value} <- Props];
json_match([_ | _] = NonEmptyList) ->
  [to_json(X) || X <- NonEmptyList];
json_match(Any) -> Any.

is_char(C) -> erlang:is_integer(C) andalso C >= 0 andalso C =< 255.

is_string([N | _] = PossibleString) when erlang:is_number(N) -> lists:all(fun is_char/1, PossibleString);
is_string(_)                                                 -> false.

to_binary(A) when erlang:is_atom(A) -> erlang:atom_to_binary(A, latin1);
to_binary(B) when erlang:is_binary(B) -> B;
to_binary(I) when erlang:is_integer(I) -> to_binary(erlang:integer_to_list(I));
to_binary(F) when erlang:is_float(F) -> erlang:float_to_binary(F, [{decimals, 9}, compact]);
to_binary(L) when erlang:is_list(L) ->  erlang:iolist_to_binary(L).

parse(String) ->
  %{ok, Tokens, _EndLine} = erl_scan:string(String),
  {ok, Tokens, _EndLine} = erl_scan:string(String ++ "."),
  {ok, AbsForm} = erl_parse:parse_exprs(Tokens),
  {value, Value, _Bs} = erl_eval:exprs(AbsForm, erl_eval:new_bindings()),
  Value.