-module('__ENV__').
-moduledoc """
Bring Elixir-style __ENV__ macro and macro calls into Erlang.

## Usage

Apply the parse transform to your module:

    -compile({parse_transform, '__ENV__'}).

Then you can use the macro everywhere in your code:

    io:format("~p~n", [__ENV__])

## But WHY!??

Well, you can call Elixir macros with it directly from Erlang. Here is how:

In Elixir macros look just like ordinary functions on the surface. You can call
them by the same `Module.macro_name(args)` syntax as you call functions.  But
macros are not functions.  They are compile time AST transformations.  They
receive ASTs as arguments, and they return ASTs that should take the place of
the macro call. You can call `Logger.info("hello")` from Elixir, but
`'Elixir.Logger':info(<<"hello">>)` won't work, because this is actually an
Elixir macro. But you can hack this from Erlang, like this:

    -define(APPLY_MACRO(Module, Macro, Args),
      'Elixir.Code':eval_quoted(
        Module,
        list_to_atom(string:concat("MACRO-", atom_to_list(Macro))),
        [__ENV__ | Args]
      )
    ).

    ?APPLY_MACRO('Elixir.Logger', :info, [<<"hello">>])

""".

-export([parse_transform/2]).

parse_transform(Forms, _Opts) ->
    File = get_file(Forms),
    Module = get_module(Forms),
    Imports = get_imports(Forms),
    transform_forms(Forms, File, Module, Imports).

transform_forms([], _File, _Module, _Imports) ->
    [];
transform_forms([{attribute, _, file, {NewFile, _}} = Form | Rest], _File, Module, Imports) ->
    [Form | transform_forms(Rest, NewFile, Module, Imports)];
transform_forms([{function, Loc, Name, Arity, Clauses} | Rest], File, Module, Imports) ->
    NewClauses = [transform_clause(C, File, Module, Imports, Name, Arity) || C <- Clauses],
    [{function, Loc, Name, Arity, NewClauses} | transform_forms(Rest, File, Module, Imports)];
transform_forms([Form | Rest], File, Module, Imports) ->
    [Form | transform_forms(Rest, File, Module, Imports)].

transform_clause({clause, Loc, Pattern, Guards, Body}, File, Module, Imports, FunName, FunArity) ->
    NewPattern = [transform_pattern(P, File, Module, Imports, FunName, FunArity) || P <- Pattern],
    NewGuards = transform_guards(Guards, File, Module, Imports, FunName, FunArity),
    NewBody = [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Body],
    {clause, Loc, NewPattern, NewGuards, NewBody}.

transform_guards(Guards, File, Module, Imports, FunName, FunArity) ->
    [[transform_expr(G, File, Module, Imports, FunName, FunArity) || G <- Gs] || Gs <- Guards].

transform_pattern({var, Loc, '__ENV__'}, File, Module, Imports, FunName, FunArity) ->
    macro_env_pattern(Loc, File, Module, Imports, FunName, FunArity);
transform_pattern({tuple, Loc, Es}, File, Module, Imports, FunName, FunArity) ->
    {tuple, Loc, [transform_pattern(E, File, Module, Imports, FunName, FunArity) || E <- Es]};
transform_pattern({cons, Loc, H, T}, File, Module, Imports, FunName, FunArity) ->
    {cons, Loc, transform_pattern(H, File, Module, Imports, FunName, FunArity),
                transform_pattern(T, File, Module, Imports, FunName, FunArity)};
transform_pattern({match, Loc, P1, P2}, File, Module, Imports, FunName, FunArity) ->
    {match, Loc, transform_pattern(P1, File, Module, Imports, FunName, FunArity),
                 transform_pattern(P2, File, Module, Imports, FunName, FunArity)};
transform_pattern({map, Loc, Assocs}, File, Module, Imports, FunName, FunArity) ->
    NewAssocs = [transform_pattern(A, File, Module, Imports, FunName, FunArity) || A <- Assocs],
    {map, Loc, NewAssocs};
transform_pattern({map_field_exact, Loc, Key, Value}, File, Module, Imports, FunName, FunArity) ->
    {map_field_exact, Loc, transform_pattern(Key, File, Module, Imports, FunName, FunArity),
                           transform_pattern(Value, File, Module, Imports, FunName, FunArity)};
transform_pattern({record, Loc, Name, Fields}, File, Module, Imports, FunName, FunArity) ->
    NewFields = [transform_pattern(F, File, Module, Imports, FunName, FunArity) || F <- Fields],
    {record, Loc, Name, NewFields};
transform_pattern({record_field, Loc, Name, Value}, File, Module, Imports, FunName, FunArity) ->
    {record_field, Loc, Name, transform_pattern(Value, File, Module, Imports, FunName, FunArity)};
transform_pattern({op, Loc, Op, LHS, RHS}, File, Module, Imports, FunName, FunArity) ->
    {op, Loc, Op, transform_pattern(LHS, File, Module, Imports, FunName, FunArity),
                  transform_pattern(RHS, File, Module, Imports, FunName, FunArity)};
transform_pattern({op, Loc, Op, Expr}, File, Module, Imports, FunName, FunArity) ->
    {op, Loc, Op, transform_pattern(Expr, File, Module, Imports, FunName, FunArity)};
transform_pattern({bin, Loc, Elements}, File, Module, Imports, FunName, FunArity) ->
    NewElements = [transform_pattern(E, File, Module, Imports, FunName, FunArity) || E <- Elements],
    {bin, Loc, NewElements};
transform_pattern({bin_element, Loc, Pat, Size, TSL}, File, Module, Imports, FunName, FunArity) ->
    NewPat = transform_pattern(Pat, File, Module, Imports, FunName, FunArity),
    NewSize = case Size of
        default -> default;
        _ -> transform_pattern(Size, File, Module, Imports, FunName, FunArity)
    end,
    {bin_element, Loc, NewPat, NewSize, TSL};
transform_pattern(Pattern, _, _, _, _, _) ->
    Pattern.

transform_expr({var, Loc, '__ENV__'}, File, Module, Imports, FunName, FunArity) ->
    macro_env(Loc, File, Module, Imports, FunName, FunArity);
transform_expr({call, Loc, Fun, Args}, File, Module, Imports, FunName, FunArity) ->
    NewArgs = [transform_expr(A, File, Module, Imports, FunName, FunArity) || A <- Args],
    {call, Loc, transform_expr(Fun, File, Module, Imports, FunName, FunArity), NewArgs};
transform_expr({match, Loc, P, E}, File, Module, Imports, FunName, FunArity) ->
    {match, Loc, transform_pattern(P, File, Module, Imports, FunName, FunArity),
                 transform_expr(E, File, Module, Imports, FunName, FunArity)};
transform_expr({tuple, Loc, Es}, File, Module, Imports, FunName, FunArity) ->
    {tuple, Loc, [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Es]};
transform_expr({cons, Loc, H, T}, File, Module, Imports, FunName, FunArity) ->
    {cons, Loc, transform_expr(H, File, Module, Imports, FunName, FunArity),
                transform_expr(T, File, Module, Imports, FunName, FunArity)};
transform_expr({'case', Loc, Expr, Clauses}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {'case', Loc, NewExpr, NewClauses};
transform_expr({'if', Loc, Clauses}, File, Module, Imports, FunName, FunArity) ->
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {'if', Loc, NewClauses};
transform_expr({'receive', Loc, Clauses}, File, Module, Imports, FunName, FunArity) ->
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {'receive', Loc, NewClauses};
transform_expr({'receive', Loc, Clauses, After, AfterBody}, File, Module, Imports, FunName, FunArity) ->
    NewClauses   = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    NewAfter     = transform_expr(After, File, Module, Imports, FunName, FunArity),
    NewAfterBody = [transform_expr(A, File, Module, Imports, FunName, FunArity) || A <- AfterBody],
    {'receive', Loc, NewClauses, NewAfter, NewAfterBody};
transform_expr({'try', Loc, Body, CaseClauses, CatchClauses, After}, File, Module, Imports, FunName, FunArity) ->
    NewBody  = [transform_expr(B, File, Module, Imports, FunName, FunArity) || B <- Body],
    NewCase  = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- CaseClauses],
    NewCatch = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- CatchClauses],
    NewAfter = [transform_expr(A, File, Module, Imports, FunName, FunArity) || A <- After],
    {'try', Loc, NewBody, NewCase, NewCatch, NewAfter};
transform_expr({'fun', Loc, {clauses, Clauses}}, File, Module, Imports, FunName, FunArity) ->
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {'fun', Loc, {clauses, NewClauses}};
transform_expr({block, Loc, Body}, File, Module, Imports, FunName, FunArity) ->
    NewBody  = [transform_expr(B, File, Module, Imports, FunName, FunArity) || B <- Body],
    {block, Loc, NewBody};
transform_expr({lc, Loc, Expr, Qualifiers}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewQuals = [transform_expr(Q, File, Module, Imports, FunName, FunArity) || Q <- Qualifiers],
    {lc, Loc, NewExpr, NewQuals};
transform_expr({bc, Loc, Expr, Qualifiers}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewQuals = [transform_expr(Q, File, Module, Imports, FunName, FunArity) || Q <- Qualifiers],
    {bc, Loc, NewExpr, NewQuals};
transform_expr({map, Loc, Assocs}, File, Module, Imports, FunName, FunArity) ->
    NewAssocs = [transform_expr(A, File, Module, Imports, FunName, FunArity) || A <- Assocs],
    {map, Loc, NewAssocs};
transform_expr({map, Loc, Expr, Assocs}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewAssocs = [transform_expr(A, File, Module, Imports, FunName, FunArity) || A <- Assocs],
    {map, Loc, NewExpr, NewAssocs};
transform_expr({op, Loc, Op, LHS, RHS}, File, Module, Imports, FunName, FunArity) ->
    {op, Loc, Op, transform_expr(LHS, File, Module, Imports, FunName, FunArity),
                  transform_expr(RHS, File, Module, Imports, FunName, FunArity)};
transform_expr({op, Loc, Op, Expr}, File, Module, Imports, FunName, FunArity) ->
    {op, Loc, Op, transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({record, Loc, Name, Fields}, File, Module, Imports, FunName, FunArity) ->
    NewFields = [transform_expr(F, File, Module, Imports, FunName, FunArity) || F <- Fields],
    {record, Loc, Name, NewFields};
transform_expr({record_field, Loc, Expr, Name, Field}, File, Module, Imports, FunName, FunArity) ->
    {record_field, Loc, transform_expr(Expr, File, Module, Imports, FunName, FunArity), Name, Field};
transform_expr({clause, Loc, Pattern, Guards, Body}, File, Module, Imports, FunName, FunArity) ->
    NewPattern = [transform_pattern(P, File, Module, Imports, FunName, FunArity) || P <- Pattern],
    NewGuards = transform_guards(Guards, File, Module, Imports, FunName, FunArity),
    NewBody = [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Body],
    {clause, Loc, NewPattern, NewGuards, NewBody};
transform_expr({map_field_assoc, Loc, Key, Value}, File, Module, Imports, FunName, FunArity) ->
    {map_field_assoc, Loc, transform_expr(Key, File, Module, Imports, FunName, FunArity),
                           transform_expr(Value, File, Module, Imports, FunName, FunArity)};
transform_expr({map_field_exact, Loc, Key, Value}, File, Module, Imports, FunName, FunArity) ->
    {map_field_exact, Loc, transform_expr(Key, File, Module, Imports, FunName, FunArity),
                           transform_expr(Value, File, Module, Imports, FunName, FunArity)};
transform_expr({generate, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {generate, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                    transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({b_generate, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {b_generate, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                      transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({record_field, Loc, Name, Value}, File, Module, Imports, FunName, FunArity) ->
    {record_field, Loc, Name, transform_expr(Value, File, Module, Imports, FunName, FunArity)};
transform_expr({bin, Loc, Elements}, File, Module, Imports, FunName, FunArity) ->
    NewElements = [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Elements],
    {bin, Loc, NewElements};
transform_expr({bin_element, Loc, Expr, Size, TSL}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewSize = case Size of
        default -> default;
        _ -> transform_expr(Size, File, Module, Imports, FunName, FunArity)
    end,
    {bin_element, Loc, NewExpr, NewSize, TSL};
transform_expr({'fun', Loc, {function, M, F, A}}, File, Module, Imports, FunName, FunArity)
    when is_tuple(M) ->
    {'fun', Loc, {function, transform_expr(M, File, Module, Imports, FunName, FunArity),
                            transform_expr(F, File, Module, Imports, FunName, FunArity),
                            transform_expr(A, File, Module, Imports, FunName, FunArity)}};
transform_expr({'catch', Loc, Expr}, File, Module, Imports, FunName, FunArity) ->
    {'catch', Loc, transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({named_fun, Loc, Name, Clauses}, File, Module, Imports, FunName, FunArity) ->
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {named_fun, Loc, Name, NewClauses};
transform_expr({record, Loc, Expr, Name, Fields}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewFields = [transform_expr(F, File, Module, Imports, FunName, FunArity) || F <- Fields],
    {record, Loc, NewExpr, Name, NewFields};
transform_expr({remote, Loc, ModExpr, FunExpr}, File, Module, Imports, FunName, FunArity) ->
    {remote, Loc, transform_expr(ModExpr, File, Module, Imports, FunName, FunArity),
                  transform_expr(FunExpr, File, Module, Imports, FunName, FunArity)};
transform_expr({'maybe', Loc, Body}, File, Module, Imports, FunName, FunArity) ->
    NewBody = [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Body],
    {'maybe', Loc, NewBody};
transform_expr({'maybe', Loc, Body, {'else', ElseLoc, Clauses}}, File, Module, Imports, FunName, FunArity) ->
    NewBody = [transform_expr(E, File, Module, Imports, FunName, FunArity) || E <- Body],
    NewClauses = [transform_expr(C, File, Module, Imports, FunName, FunArity) || C <- Clauses],
    {'maybe', Loc, NewBody, {'else', ElseLoc, NewClauses}};
transform_expr({maybe_match, Loc, P, E}, File, Module, Imports, FunName, FunArity) ->
    {maybe_match, Loc, transform_pattern(P, File, Module, Imports, FunName, FunArity),
                       transform_expr(E, File, Module, Imports, FunName, FunArity)};
transform_expr({mc, Loc, Expr, Qualifiers}, File, Module, Imports, FunName, FunArity) ->
    NewExpr = transform_expr(Expr, File, Module, Imports, FunName, FunArity),
    NewQuals = [transform_expr(Q, File, Module, Imports, FunName, FunArity) || Q <- Qualifiers],
    {mc, Loc, NewExpr, NewQuals};
transform_expr({m_generate, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {m_generate, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                      transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({generate_strict, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {generate_strict, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                           transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({b_generate_strict, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {b_generate_strict, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                              transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({m_generate_strict, Loc, Pattern, Expr}, File, Module, Imports, FunName, FunArity) ->
    {m_generate_strict, Loc, transform_pattern(Pattern, File, Module, Imports, FunName, FunArity),
                              transform_expr(Expr, File, Module, Imports, FunName, FunArity)};
transform_expr({zip, Loc, Qualifiers}, File, Module, Imports, FunName, FunArity) ->
    NewQuals = [transform_expr(Q, File, Module, Imports, FunName, FunArity) || Q <- Qualifiers],
    {zip, Loc, NewQuals};
transform_expr(Expr, _, _, _, _, _) ->
    Expr.

macro_env(Loc, File, Module, Imports, FunName, FunArity) ->
    macro_env(Loc, File, Module, Imports, FunName, FunArity, map_field_assoc).

macro_env_pattern(Loc, File, Module, Imports, FunName, FunArity) ->
    macro_env(Loc, File, Module, Imports, FunName, FunArity, map_field_exact).

macro_env(Loc, File, Module, Imports, FunName, FunArity, FieldType) ->
    Line = get_line(Loc),
    {map, Loc, [
      {FieldType, Loc, {atom, Loc, '__struct__'}, {atom, Loc, 'Elixir.Macro.Env'}},
      {FieldType, Loc, {atom, Loc, file}, {bin, Loc, [{bin_element, Loc, {string, Loc, File}, default, default}]}},
      {FieldType, Loc, {atom, Loc, line}, {integer, Loc, Line}},
      {FieldType, Loc, {atom, Loc, module}, {atom, Loc, Module}},
      {FieldType, Loc, {atom, Loc, function}, {tuple, Loc, [{atom, Loc, FunName}, {integer, Loc, FunArity}]}},
      {FieldType, Loc, {atom, Loc, context}, {atom, Loc, nil}},
      {FieldType, Loc, {atom, Loc, functions}, imports(Loc, Imports)},
      {FieldType, Loc, {atom, Loc, aliases}, {nil, Loc}},
      {FieldType, Loc, {atom, Loc, lexical_tracker}, {atom, Loc, nil}},
      {FieldType, Loc, {atom, Loc, macro_aliases}, {nil, Loc}},
      {FieldType, Loc, {atom, Loc, versioned_vars}, {map, Loc, []}},
      {FieldType, Loc, {atom, Loc, tracers}, {nil, Loc}},
      {FieldType, Loc, {atom, Loc, requires}, {nil, Loc}},
      {FieldType, Loc, {atom, Loc, macros}, {nil, Loc}},
      {FieldType, Loc, {atom, Loc, context_modules}, list(Loc, [{atom, Loc, Module}])}
    ]}.

get_file([{attribute, _, file, {File, _}} | _]) -> File;
get_file([_ | Rest]) -> get_file(Rest);
get_file([]) -> "nofile".

get_module([{attribute, _, module, Module} | _]) -> Module;
get_module([_ | Rest]) -> get_module(Rest);
get_module([]) -> undefined.

get_imports(Forms) -> [{Mod, Funs} || {attribute, _, import, {Mod, Funs}} <- Forms].

get_line({Line, _}) when is_integer(Line) -> Line;
get_line(Line) when is_integer(Line) -> Line.

imports(Loc, Imports) -> list(Loc, [import_tuple(Loc, Mod, Funs) || {Mod, Funs} <- Imports]).

import_tuple(Loc, Mod, Funs) ->
    FunsAST = list(Loc, [{tuple, Loc, [{atom, Loc, F}, {integer, Loc, A}]} || {F, A} <- Funs]),
    {tuple, Loc, [{atom, Loc, Mod}, FunsAST]}.

list(Loc, []) -> {nil, Loc};
list(Loc, [H | T]) -> {cons, Loc, H, list(Loc, T)}.