filter.rb

module BannedWordFilter
  class Filter
    class << self

      BANNED_WORDS = %w(
        fuck
        shit
        banned
      )

      BANNED_WORDS_REGEX = /(#{BANNED_WORDS.join('|')})/i

      def run!(text)
        filtered = text.dup.gsub(BANNED_WORDS_REGEX) do |match|
          first_char = match[0]
          middle_chars = match[1...-1]
          last_char = match[-1]

          "#{first_char}#{'*' * middle_chars.size}#{last_char}"
        end

        Result.new(text, filtered)
      end

    end
  end

  class Result

    def initialize(original, clean)
      @original, @clean = original, clean
    end

    def original_text
      @original
    end

    def clean_text
      @clean
    end

    def clean?
      @original == @clean
    end

  end
end

def log_result(r)
  puts
  puts "Original: #{r.original_text}"
  puts "Cleaned: #{r.clean_text}"
  puts "Clean?: #{r.clean?}"
  puts
end

log_result(BannedWordFilter::Filter.run!("This is a sentence."))
log_result(BannedWordFilter::Filter.run!("This is a fucking sentence."))
log_result(BannedWordFilter::Filter.run!("This is a fucking sentence here's a shit."))
log_result(BannedWordFilter::Filter.run!("This is a fucking sentence here's a shit banned."))