input.txt

The heat bloomed                  in December .VB
as the carnival  season .CV
kicked into gear. .LP
Nearly helpless with sun and glare, I avoided Rio's brilliant .RP
sidewalks
 and glittering beaches,
panting in dark     corners
and waiting out the inverted southern summer. .JU

text.erl

-module(text).
-export([filling/2, show_file_contents/1]).

filling(FileName, LineLength) ->
    FileContents = get_file_contents(FileName),
    filling(FileContents, LineLength, []).

filling([], _LineLength, ACC) -> lists:reverse(ACC);
filling(FileContents, LineLength, ACC) ->
    {Line, Rest} = take_line(FileContents, LineLength, 0, []),
    filling(Rest, LineLength, [Line|ACC]).

take_line([Word | Contents], _LineLength, _CurrLength, ACC) when Word == ".VB" ->
    Line = string:join(lists:reverse(ACC), " "),
    {Line, Contents};
take_line([Word | Contents] , LineLength, _CurrLength, ACC) when Word == ".CV" ->
    Line = string:join(lists:reverse(ACC), " "),
    {center(Line, LineLength), Contents};
take_line([Word | Contents], LineLength, _CurrLength, ACC) when Word == ".LP" ->
    Line = string:join(lists:reverse(ACC), " "),
    {left_fill(Line, LineLength), Contents};
take_line([Word | Contents], LineLength, _CurrLength, ACC) when Word == ".RP" ->
    Line = string:join(lists:reverse(ACC), " "),
    {right_fill(Line, LineLength), Contents};
take_line([Word | Contents], LineLength, CurrLength, ACC) when Word == ".JU" ->
    RemainingLength = LineLength - CurrLength + 1,
    Line = string:join(lists:reverse(ACC),
                       lists:duplicate(RemainingLength div (length(ACC)-1),
                                       " ")),
    {Line, Contents};
take_line([Word | Rest], LineLength, CurrLength, ACC) when CurrLength + length(Word) =< LineLength ->
    take_line(Rest, LineLength, CurrLength+length(Word)+1, [Word|ACC]);
take_line(Contents, _LineLength, _CurrLength, ACC) ->
    {string:join(lists:reverse(ACC), " "), Contents}.

center(Line, LineLength) ->
    left_fill(right_fill(Line, LineLength div 2),
              LineLength div 2 + LineLength rem 2).
left_fill(Line, LineLength) ->
    RemainingLength = LineLength-length(Line),

    Line ++
        lists:duplicate(RemainingLength, " ").
right_fill(Line, LineLength) ->
    RemainingLength = LineLength-length(Line),

    lists:duplicate(RemainingLength, " ") ++
        Line.

% Get the contents of a text file into a list of words.

get_file_contents(Name) ->
    {ok,Contents} = file:read_file(Name),

    string:lexemes(unicode:characters_to_list(Contents),
                  " \r\n\t").

% Show the contents of a list of strings.
% Can be used to check the results of calling get_file_contents.

show_file_contents([L|Ls]) ->
    io:format("~s~n",[L]),
    show_file_contents(Ls);
 show_file_contents([]) ->
    ok.