comparing 2 files

comparison.rb

class Comparison
  def self.new(string_one, string_two)
    # Define variables to manipulate later on
    unchanged, addition = "", ""
    all_unchanged, all_additions = [], []

    # Determine which file has the largest amount of characters
    if (string_one <=> string_two) < 0
      num_chars = string_two.length
    else
      num_chars = string_one.length
    end

    num_chars.times do |n|
      case
      # WHEN the character in position n is equal in both files 
      when string_one[n] == string_two[n]
        # ADD the character to the unchanged string
        unchanged += string_one[n]

      # WHEN the character in position n is different in one of the files
      when string_one[n] != string_two[n]
        # ADD the character to the addition string
        addition += string_two[n]

        # IF the next character is both files equal again, we need to place
        # the variables into the arrays so that the files can be eventually
        # put back together again.
        unless string_one[n + 1] == string_two[n + 1]
          # MERGE unchanged string into the unchanged array
          all_unchanged << unchanged

          # MERGE addition string into the additions array
          all_additions << addition

          # RESET string variables to write new content
          unchanged, addition = "", ""
        end
      end
    end

    return "Unchanged: '#{unchanged}', Added  '#{addition}'. All_Unchanged: '#{all_unchanged}', All_Added: '#{all_additions}'."
  end
end

outputs.rb

require "./comparison.rb"

Comparison.new("Hello", "Hello")
#=> Unchanged: 'Hello', Added: ''. All_Unchanged: '[]', All_Added: '[]'.

#=> <DESIRED OUTPUT> Unchanged: '', Added: ''. All_Unchanged: ["Hello"], All_Added: '[]'.

Comparison.new("Hello", "H123llo")
#=> "Unchanged: '', Added S: ''. All_Unchanged: '[\"H\", \"\", \"\", \"\"]', All_Added: '[\"1\", \"2\", \"3\", \"l\"]'." 

#=> <DESIRED OUTPUT> Unchanged: '', Added: ''. All_Unchanged: ["H", "llo"], All_Added: '["123"]'.

Comparison.new("Welcome to GitHub", "We1lcome T0 github")
#=> "Unchanged: '', Added S: ''. All_Unchanged: '[\"We\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\"]', All_Added: '[\"1\", \"l\", \"c\", \"o\", \"m\", \"e\", \" \", \"T\", \"0\", \" \", \"g\", \"i\", \"t\", \"h\", \"u\"]'." 

#=> <DESIRED OUTPUT> Unchanged: '', Added: ''. All_Unchanged: ["We", "lcome T", "it", "ub"], All_Added: '["1", "0 g", "h"]'.