add SHA-1 question

lib/extreme_startup/question_factory.rb

@@ -2,6 +2,7 @@
 
 require 'set'
 require 'prime'
+require 'digest/sha1'
 
 module ExtremeStartup
   class Question
@@ -627,6 +628,43 @@ module ExtremeStartup
     end
   end
 
+  class Sha1Question < GetQuestion
+    def initialize(player, word=nil)
+      if word
+        @word = word
+      else
+        size = rand(5) + 5
+        @word = generate_string(size)
+      end
+    end
+
+    def as_text
+      "what is the SHA-1 hash of #{@word}"
+    end
+  private
+    def correct_answer
+      Digest::SHA1.hexdigest @word
+    end
+
+    def generate_string(size)
+      random_chars[0..size].reduce(:+)
+    end
+
+    def random_chars
+      randoms = Set.new
+      loop do
+        is_upper = rand(2)
+        if is_upper == 1
+          c = 'A'.ord
+        else
+          c = 'a'.ord
+        end
+        randoms << (c + rand(26)).chr
+        return randoms.to_a if randoms.size >= 10
+      end
+    end
+  end
+
   class QuestionFactory
     attr_reader :round