rebar3_format

%% @doc Default formatter for modules that use the AST to prettyprint code
-module(rebar3_ast_formatter).

-include_lib("kernel/include/file.hrl").

-export([format/3]).

-callback format(erl_syntax:forms(), [pos_integer()], rebar3_formatter:opts()) ->
                    string().

%% @doc Format a file.
%%      Apply formatting rules to a file containing erlang code.
%%      Use <code>Opts</code> to configure the formatter.
-spec format(file:filename_all(), module(), rebar3_formatter:opts()) ->
                rebar3_formatter:result().
format(File, Formatter, Opts) ->
    AST = get_ast(File, Opts),
    QuickAST = get_quick_ast(File),
    Comments = get_comments(File),
    {ok, Original} = file:read_file(File),
    Formatted = format(File, AST, Formatter, Comments, Opts),
    Result =
        case Formatted of
            Original ->
                unchanged;
            _ ->
                changed
        end,
    case maybe_save_file(maps:get(output_dir, Opts), File, Formatted) of
        none ->
            Result;
        NewFile ->
            case get_quick_ast(NewFile) of
                QuickAST ->
                    Result;
                _ ->
                    erlang:error({modified_ast, File, NewFile})
            end
    end.

get_ast(File, Opts) ->
    DodgerOpts =
        [{scan_opts, [text]}, no_fail]
        ++ [parse_macro_definitions || maps:get(parse_macro_definitions, Opts, true)],
    case ktn_dodger:parse_file(File, DodgerOpts) of
        {ok, AST} ->
            case [Error || {error, Error} <- AST] of
                [] ->
                    AST;
                [Error | _] ->
                    erlang:error({cant_parse, File, Error})
            end;
        {error, OpenError} ->
            erlang:error({cant_parse, File, OpenError})
    end.

get_quick_ast(File) ->
    case ktn_dodger:quick_parse_file(File) of
        {ok, AST} ->
            remove_line_numbers(AST);
        {error, OpenError} ->
            erlang:error({cant_parse, File, OpenError})
    end.

%% @doc Removes line numbers from ASTs to allow for "semantic" comparison
remove_line_numbers(AST) when is_list(AST) ->
    lists:map(fun remove_line_numbers/1, AST);
remove_line_numbers(AST) when is_tuple(AST) ->
    [Type, _Line | Rest] = tuple_to_list(AST),
    list_to_tuple([Type, no | remove_line_numbers(Rest)]);
remove_line_numbers(AST) ->
    AST.

get_comments(File) ->
    erl_comment_scan:file(File).

format(File, AST, Formatter, Comments, Opts) ->
    WithComments =
        erl_recomment:recomment_forms(
            erl_syntax:form_list(AST), Comments),
    Formatted = Formatter:format(WithComments, empty_lines(File), Opts),
    insert_last_line(iolist_to_binary(Formatted)).

empty_lines(File) ->
    {ok, Data} = file:read_file(File),
    List = binary:split(Data, [<<"\n">>], [global, trim]),
    {ok, NonEmptyLineRe} = re:compile("\\S"),
    {Res, _} =
        lists:foldl(fun(Line, {EmptyLines, N}) ->
                       case re:run(Line, NonEmptyLineRe) of
                           {match, _} -> {EmptyLines, N + 1};
                           nomatch -> {[N | EmptyLines], N + 1}
                       end
                    end,
                    {[], 1},
                    List),
    lists:reverse(Res).

insert_last_line(Formatted) ->
    {ok, Re} = re:compile("[\n]+$"),
    case re:run(Formatted, Re) of
        {match, _} ->
            re:replace(Formatted, Re, "\n", [{return, binary}]);
        nomatch ->
            <<Formatted/binary, "\n">>
    end.

maybe_save_file(none, _File, _Formatted) ->
    none;
maybe_save_file(current, File, Formatted) ->
    ok = file:write_file(File, Formatted),
    File;
maybe_save_file(OutputDir, File, Formatted) ->
    OutFile =
        filename:join(
            filename:absname(OutputDir), File),
    ok = filelib:ensure_dir(OutFile),
    {ok, FileInfo} = file:read_file_info(File),
    ok = file:write_file(OutFile, Formatted),
    ok = file:change_mode(OutFile, FileInfo#file_info.mode),
    OutFile.