You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: completion_mode.rb
    path of file: ./repos/sup/lib/sup/modes
    
    the code of the file until where you have to start completion: module Redwood

class CompletionMode < ScrollMode
  INTERSTITIAL = "  "

  def initialize list, opts={}
    @list = list
    @header = opts[:header]
    @prefix_len = opts[:prefix_len]
    @lines = nil
    super :slip_rows => 1, :twiddles => false
  end

  def lines
    update_lines unless @
    
  def roll; if at_bottom? then jump_to_start else page_down end end

private

  def update_lines
    max_length = @list.max_of { |s| s.length }
    num_per = [1, buffer.content_width / (max_length + INTERSTITIAL.length)].max
    @lines = [@header].compact
    @list.each_with_index do |s, i|
      if @prefix_len
        @lines << [] if i % num_per == 0
        if @prefix_len < s.length
          prefix = s[0 ... @prefix_len]
          suffix = s[(@prefix_len + 1) .. -1]
          char = s[@prefix_len].chr

          @lines.last += [[:text_color, sprintf("%#{max_length - suffix.length - 1}s", prefix)],
                          [:completion_character_color, char],
                          [:text_color, suffix + INTERSTITIAL]]
        else
          @lines.last += [[:text_color, sprintf("%#{max_length}s#{INTERSTITIAL}", s)]]
        end
      else
        @lines << "" if i % num_per == 0
        @lines.last += sprintf "%#{max_length}s#{INTERSTITIAL}", s
      end
    end