text_align_justify_solution.rb

def justify(text, width)
  return if text.nil? || width.nil? || width.negative?
    
  words = text.split(' ')
  rows = group_words_into_rows(words, width)
  rows = pad_rows(rows, width)
  rows.map(&:join).join("\n")
end

def group_words_into_rows(words, width)
  width = 1 if width.zero?
  length = 0
  
  rows = words.group_by do |word|
    length += 1 unless length.zero?
    length += word.length
    length / width
  end
  
  # Not strictly necessary but ensures a stabile sort
  rows.sort_by { |length, row| length }.map { |_, row| row }
end

def pad_rows(rows, width)
  padded_rows = rows.map { |row| pad_row(row, width) }
  
  # Last row shouldn't be padded
  if rows.count > 1
    padded_rows[0..-2] + [rows[-1]]
  else
    padded_rows
  end
end

def pad_row(row, width)
  length = row.map(&:length).sum
  
  spaces_count = width - length
  positions = row.length - 1
    
  return row if positions <= 0
  return row if spaces_count <= 0
  
  spaces_per_position, extra_spaces_for_positions = spaces_count.divmod(positions)
  paddings = build_paddings(positions, spaces_per_position, extra_spaces_for_positions)
  
  row.zip(paddings).flatten.compact
end

def build_paddings(positions, spaces_per_position, extra_spaces_for_positions)
  spaces = ' ' * spaces_per_position
  
  (1..positions).map do |_|
    extra_spaces = if extra_spaces_for_positions.positive?
      extra_spaces_for_positions -= 1
      ' '
    else
      ''
    end
    
    spaces + extra_spaces
  end
end