%% -*- mode: erlang; tab-width: 4; indent-tabs-mode: 1; st-rulers: [70] -*-
%% vim: ts=4 sw=4 ft=erlang noet
%%%-------------------------------------------------------------------
%%% @author Andrew Bennett <potatosaladx@gmail.com>
%%% @copyright 2017-2019, Andrew Bennett
%%% @doc
%%%
%%% @end
%%% Created :  24 Feb 2018 by Andrew Bennett <potatosaladx@gmail.com>
%%%-------------------------------------------------------------------
-module(jose_base).

%% API
-export([calculate_shift/1]).
-export([calculate_pairs/2]).

%% parse_transform callbacks
-export([parse_transform/2]).

%%%===================================================================
%%% API functions
%%%===================================================================

calculate_shift(Table) when is_list(Table) ->
	erlang:round(math:log2(length(Table))).

calculate_pairs(Table, Type) when Type == sensitive orelse Type == upper ->
	Shift = calculate_shift(Table),
	do_calculate_pairs(Table, Table, Shift, []).

%% @private
do_calculate_pairs([{V0, C0} | Rest], Table, Shift, Acc0) ->
	Acc1 = do_calculate_pairs_permutation(V0 bsl Shift, C0 bsl 8, Table, Acc0),
	do_calculate_pairs(Rest, Table, Shift, Acc1);
do_calculate_pairs([], _Table, _Shift, Acc) ->
	lists:reverse(Acc).

%% @private
do_calculate_pairs_permutation(V0, C0, [{V1, C1} | Rest], Acc0) ->
	V = V0 + V1,
	C = C0 + C1,
	Acc1 = [{V, C} | Acc0],
	do_calculate_pairs_permutation(V0, C0, Rest, Acc1);
do_calculate_pairs_permutation(_, _, [], Acc) ->
	Acc.

%%%===================================================================
%%% parse_transform callbacks
%%%===================================================================

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

%%%-------------------------------------------------------------------
%%% Internal functions
%%%-------------------------------------------------------------------

%% @private
walk_ast(Acc, []) ->
	lists:reverse(Acc);
walk_ast(Acc, [{function, Line, Name, Arity, Clauses} | Ast]) ->
	walk_ast([{function, Line, Name, Arity, walk_clauses([], Clauses)} | Acc], Ast);
walk_ast(Acc, [Form | Ast]) ->
	walk_ast([Form | Acc], Ast).

%% @private
walk_clauses(Acc, []) ->
	lists:reverse(Acc);
walk_clauses(Acc, [{clause, Line, Arguments, Guards, Body} | Ast]) ->
	walk_clauses([{clause, Line, Arguments, Guards, walk_body([], Body)} | Acc], Ast).

%% @private
walk_body(Acc, []) ->
	lists:reverse(Acc);
walk_body(Acc, [Statement | Ast]) ->
	walk_body([transform_statement(Statement) | Acc], Ast).

%% @private
transform_statement(Statement = {call, Line, {remote, _Line1, {atom, _Line2, ?MODULE}, {atom, _Line3, Function}}, Arguments}) ->
	case transform_call(Function, Line, Arguments) of
		{ok, NewStatement} ->
			NewStatement;
		error ->
			Statement
	end;
transform_statement({match, Line, Pattern, Expression}) ->
	{match, Line, Pattern, transform_expression(Expression)};
transform_statement(Statement) ->
	Statement.

%% @private
transform_expression({bc, Line1, {bin, Line2, Elements}, Qualifiers}) ->
	{bc, Line1, {bin, Line2, walk_elements([], Elements)}, Qualifiers};
transform_expression(Expression) ->
	Expression.

%% @private
walk_elements(Acc, []) ->
	lists:reverse(Acc);
walk_elements(Acc, [{bin_element, Line, Statement, Size, Type} | Ast]) ->
	walk_elements([{bin_element, Line, transform_statement(Statement), Size, Type} | Acc], Ast);
walk_elements(Acc, [Element | Ast]) ->
	walk_elements([Element | Acc], Ast).

%% @private
transform_call(encode_char, _Line, [Case = {'case', _Line1, _Var, [{clause, _Line2, [{integer, _Line3, 0}], [], [{char, _Line4, _}]} | _]}]) ->
	{ok, Case};
transform_call(encode_pair, Line, [{'case', _Line1, Var, Clauses0 = [{clause, _Line2, [{integer, _Line3, 0}], [], [{char, _Line4, _}]} | _]}, {atom, _Line5, Type}]) ->
	Table = calculate_pairs([{Index, Value} || {clause, _, [{integer, _, Index}], [], [{char, _, Value}]} <- Clauses0], Type),
	Clauses1 = [{clause, Line, [{integer, Line, Index}], [], [{integer, Line, Value}]} || {Index, Value} <- Table],
	Case = {'case', Line, Var, Clauses1},
	{ok, Case};
transform_call(_Function, _Line, _Arguments) ->
	error.