class Diff::LCS::Hunk

def unified_diff
  # Calculate item number range.
  s = encode("@@ -#{unified_range(:old)} +#{unified_range(:new)} @@\n")
  # Outlist starts containing the hunk of the old file. Removing an item
  # just means putting a '-' in front of it. Inserting an item requires
  # getting it from the new file and splicing it in. We splice in
  # +num_added+ items. Remove blocks use +num_added+ because splicing
  # changed the length of outlist.
  #
  # We remove +num_removed+ items. Insert blocks use +num_removed+
  # because their item numbers -- corresponding to positions in the NEW
  # file -- don't take removed items into account.
  lo, hi, num_added, num_removed = @start_old, @end_old, 0, 0
  outlist = @data_old[lo .. hi].map { |e| e.insert(0, encode(' ')) }
  @blocks.each do |block|
    block.remove.each do |item|
      op     = item.action.to_s # -
      offset = item.position - lo + num_added
      outlist[offset][0, 1] = encode(op)
      num_removed += 1
    end
    block.insert.each do |item|
      op     = item.action.to_s # +
      offset = item.position - @start_new + num_removed
      outlist[offset, 0] = encode(op) + @data_new[item.position]
      num_added += 1
    end
  end
  s << outlist.join(encode("\n"))
end