%% -------------------------------------------------------------------
%%
%% Copyright (c) 2018 Christopher S. Meiklejohn.  All Rights Reserved.
%%
%% This file is provided to you under the Apache License,
%% Version 2.0 (the "License"); you may not use this file
%% except in compliance with the License.  You may obtain
%% a copy of the License at
%%
%%   http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing,
%% software distributed under the License is distributed on an
%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
%% KIND, either express or implied.  See the License for the
%% specific language governing permissions and limitations
%% under the License.
%%
%% -------------------------------------------------------------------

%% -----------------------------------------------------------------------------
%% @doc Parse transformation that replaces all instances of the Erlang bang
%% operator `!' with a call to `partisan:forward_message/2'.
%%
%% Example: `Pid ! hello' will be transformed to `partisan:forward_message(Pid,
%% hello)'.
%%
%% @end
%% -----------------------------------------------------------------------------
-module(partisan_transform).
-author("Christopher S. Meiklejohn <christopher.meiklejohn@gmail.com>").

%% Public API
-export([parse_transform/2]).




%% =============================================================================
%% API
%% =============================================================================



parse_transform(AST, _Options) ->
    walk_ast([], AST).




%% =============================================================================
%% PRIVATE
%% =============================================================================



%% @private
walk_ast(Acc, []) ->
    lists:reverse(Acc);

walk_ast(Acc, [{attribute, _, module, {_Module, _PmodArgs}}=H|T]) ->
    walk_ast([H|Acc], T);

walk_ast(Acc, [{attribute, _, module, _Module}=H|T]) ->
    walk_ast([H|Acc], T);

walk_ast(Acc, [{function, Line, Name, Arity, Clauses}|T]) ->
    walk_ast(
        [{function, Line, Name, Arity, walk_clauses([], Clauses)}|Acc],
        T
    );

walk_ast(Acc, [{attribute, _, record, {_Name, _Fields}}=H|T]) ->
    walk_ast([H|Acc], T);

walk_ast(Acc, [H|T]) ->
    walk_ast([H|Acc], T).


%% @private
walk_clauses(Acc, []) ->
    lists:reverse(Acc);

walk_clauses(Acc, [{clause, Line, Arguments, Guards, Body}|T]) ->
    walk_clauses(
        [{clause, Line, Arguments, Guards, walk_body([], Body)}|Acc],
        T
    ).


%% @private
walk_body(Acc, []) ->
    lists:reverse(Acc);

walk_body(Acc, [H|T]) ->
    walk_body([transform_statement(H)|Acc], T).


%% @private
transform_statement(
    {op, Line, '!', {var, Line, RemotePid}, {Type, Line, Message}}) ->
    {call,
        Line,
        {remote, Line,
            {atom, Line, partisan},
            {atom, Line, forward_message}
        },
        [{var, Line, RemotePid}, {Type, Line, Message}]
    };

transform_statement(
    {match, Line, {var, Line, RemotePid}, {call, Line, _, _} = Call}) ->
    {match, Line, {var, Line, RemotePid}, transform_statement(Call)};

transform_statement({call, Line, {atom, Line, self}, []}) ->
    {call,
        Line,
        {remote, Line, {atom, Line, partisan}, {atom, Line, self}},
        []
    };

transform_statement(Stmt) ->
    Stmt.