-module(format).
-export([fixed_line_length/2]).

%
% In word processing systems it is customary for lines to be filled
% and broken automatically, to enhance the appearance of the text.
% Input of the form
%
% The heat bloomed                  in December
%  as the      carnival  season
%                  kicked into gear.
% Nearly helpless with sun and glare, I avoided Rio's brilliant
% sidewalks
%  and glittering beaches,
% panting in dark     corners
%   and waiting out the inverted southern summer.
%
% would be transformed by filling to
%
% The heat bloomed in December as the
% carnival season kicked into gear.
% Nearly helpless with sun and glare,
% I avoided Rio's brilliant sidewalks
% and glittering beaches, panting in
% dark corners and waiting out the
% inverted southern summer.
%

% Loads a file and returns each of its
% lines (list of strings) with a constant maximum length
fixed_line_length(FileName, Length) ->
  Words = words_from_file(FileName),
  ExistWordsLongerThanLength = lists:any(fun(WordI) -> length(WordI) + 1 > Length end, Words),
  if
    ExistWordsLongerThanLength ->
      throw("There are some words longer than maximum line length");
  true ->
    format_words_in_fixed_line_length(Words, Length)
  end.

% Split lines in fixed length
format_words_in_fixed_line_length([WordI|Words], Length) ->
    format_words_in_fixed_line_length(Words, Length, "", WordI).

format_words_in_fixed_line_length([], _, Acc, CurrLine) -> Acc ++ [CurrLine];
format_words_in_fixed_line_length([WordI|Words], Length, Acc, CurrLine) ->
  CurrLineLength = length(CurrLine),
  WordILength = length(WordI),
  if
    CurrLineLength + WordILength + 1 > Length ->
      format_words_in_fixed_line_length([WordI|Words], Length, Acc ++ [CurrLine], "");
    true ->
      format_words_in_fixed_line_length(Words, Length, Acc, string:trim(CurrLine ++ " " ++ WordI))
  end.


% Return a list with a words from the file named FileName.
words_from_file(FileName) ->
    FileLines = get_file_contents(FileName),
    Words = lists:concat(
      lists:map(
        fun(FileLine) -> string:tokens(FileLine, " ") end,
        FileLines
      )
    ),
    Words.


% Get the contents of a text file into a list of lines.
% Each line has its trailing newline removed.
get_file_contents(Name) ->
    {ok,File} = file:open(Name,[read]),
    Rev = get_all_lines(File,[]),
    lists:reverse(Rev).


% Auxiliary function for get_file_contents.
% Not exported.
get_all_lines(File,Partial) ->
    case io:get_line(File,"") of
        eof -> file:close(File),
               Partial;
        Line -> {Strip,_} = lists:split(length(Line)-1,Line),
                get_all_lines(File,[Strip|Partial])
    end.