entab

#!/usr/bin/env escript

%% settabs -- set initial tab stops
%%
%% We can't generate a list/array because we don't have a MAXLINE.
%% settabs returns the TabSpace value instead.
settabs() ->
    TabSpace = 4,
    TabSpace.

%% tabpos -- return true if col is a tab stop
%%
%% Doesn't make sense in using MAXLINE since Erlang handle
%% the EOF and buffer size for us, unless we're using
%% io:get_chars/2 because the second parameter of the said
%% function is exactly a limiter.
tabpos(Col) ->
    TabSpace = settabs(),
    TabSpace - Col rem TabSpace.

%% entab -- convert runs of blanks into tabs
%%
%% BUGS
%% Is (possibly) not an exact inverse of detab.
%% It doesn't convert a single blank to a tab if it occurs
%% at a tab stop. This behavior was considered a bug in Pascal,
%% here it could be considered a bug to don't have such a bug.
entab(Input) ->
    entab(Input, 0, []).

entab([], _, Acc) ->
    ststd:putf("~p~n", [Acc]);
%% Blank/Whitespace = ASCII 32
entab([32|T], Blanks, Acc) ->
    TabSize = settabs(),
    case Blanks =:= (TabSize - 1) of
        true -> entab(T, 0, lists:concat([Acc, [9]]));
        false -> entab(T, Blanks+1, Acc)
    end;
entab([H|T], Blanks, Acc) ->
    Seq = lists:seq(1, Blanks),
    BlanksList = lists:map(fun(_) -> 32 end, Seq),
    entab(T, 0, lists:concat([Acc, BlanksList, [H]])).

main([]) ->
    Input = ststd:getf(),
    entab(Input);
main(Arg) ->
    {ok, Bin} = file:read_file(Arg),
    File = erlang:binary_to_file(Bin),
    entab(File).