Added: Vanity query parameter that you can use to choose a particular…

… alternative, e.g. to tie an advertisement banner with content of the site.

CHANGELOG

@@ -1,4 +1,5 @@
 == 1.3.0
+* Added: Vanity query parameter that you can use to choose a particular alternative, e.g. to tie an advertisement banner with content of the site.
 * Changed: Rails integration now separates use_vanity method, filters and helpers.
 * Changed: Explicit vanity_context_filter and vanity_reload_filter so you can skip them, or order filters relative to them.
 * Fixed: if metric cannot be loaded (e.g. offline, no db access) show error message for that metric but don't break dashboard.

lib/vanity/experiment/ab_test.rb

@@ -200,6 +200,13 @@ def choose
         @alternatives[index.to_i]
       end
 
+      # Returns fingerprint (hash) for given alternative.  Can be used to lookup
+      # alternative for experiment without revealing what values are available
+      # (e.g. choosing alternative from HTTP query parameter).
+      def fingerprint(alternative)
+        Digest::MD5.hexdigest("#{id}:#{alternative.id}")[-10,10]
+      end
+
 
       # -- Testing --
 

lib/vanity/rails/helpers.rb

@@ -63,6 +63,7 @@ def use_vanity(symbol = nil, &block)
         end
         around_filter :vanity_context_filter
         before_filter :vanity_reload_filter unless ::Rails.configuration.cache_classes
+        before_filter :vanity_query_parameter_filter
       end
 
     end
@@ -78,6 +79,37 @@ def vanity_context_filter
         Vanity.context = previous
       end
 
+      # This filter allows user to choose alternative in experiment using query
+      # parameter.
+      #
+      # Each alternative has a unique fingerprint (run vanity list command to
+      # see them all).  A request with the _vanity query parameter is
+      # intercepted, the alternative is chosen, and the user redirected to the
+      # same request URL sans _vanity parameter.  This only works for GET
+      # requests.
+      # 
+      # For example, if the user requests the page
+      # http://example.com/?_vanity=2907dac4de, the first alternative of the
+      # :null_abc experiment is chosen and the user redirected to
+      # http://example.com/.
+      def vanity_query_parameter_filter
+        if request.get? && params[:_vanity]
+          hashes = Array(params.delete(:_vanity))
+          Vanity.playground.experiments.each do |id, experiment|
+            if experiment.respond_to?(:alternatives)
+              experiment.alternatives.each do |alt|
+                if hash = hashes.delete(experiment.fingerprint(alt)) 
+                  experiment.chooses alt.value
+                  break
+                end
+              end
+            end
+            break if hashes.empty?
+          end
+          redirect_to url_for(params)
+        end
+      end
+
       # Before filter to reload Vanity experiments/metrics.  Enabled when
       # cache_classes is false (typically, testing environment).
       def vanity_reload_filter

test/ab_test_test.rb

@@ -68,6 +68,31 @@ def test_alternative_name
     assert_equal "option B", experiment(:abcd).alternative(:b).name
   end
 
+  def test_alternative_fingerprint_is_unique
+    ab_test :ab do
+      alternatives :a, :b
+      metrics :coolness
+    end
+    ab_test :cd do
+      alternatives :a, :b
+      metrics :coolness
+    end
+    fingerprints = Vanity.playground.experiments.map { |id, exp| exp.alternatives.map { |alt| exp.fingerprint(alt) } }.flatten
+    assert_equal 4, fingerprints.uniq.size
+  end
+
+  def test_alternative_fingerprint_is_consistent
+    ab_test :ab do
+      alternatives :a, :b
+      metrics :coolness
+    end
+    fingerprints = experiment(:ab).alternatives.map { |alt| experiment(:ab).fingerprint(alt) }
+    fingerprints.each do |fingerprint|
+      assert_match fingerprint, /^[0-9a-f]{10}$/i
+    end
+    assert_equal fingerprints.first, experiment(:ab).fingerprint(experiment(:ab).alternatives.first)
+  end
+
 
   # -- Experiment metric --
 

test/rails_test.rb

@@ -72,6 +72,31 @@ def test_vanity_identity_set_with_block
     assert_equal "576", @controller.send(:vanity_identity)
   end
 
+  # query parameter filter
+
+  def test_redirects_and_loses_vanity_query_parameter
+    get :index, :foo=>"bar", :_vanity=>"567"
+    assert_redirected_to "/use_vanity?foo=bar"
+  end
+
+  def test_sets_choices_from_vanity_query_parameter
+    first = experiment(:pie_or_cake).alternatives.first
+    # experiment(:pie_or_cake).fingerprint(first)
+    10.times do
+      @controller = nil ; setup_controller_request_and_response
+      get :index, :_vanity=>"aae9ff8081"
+      assert !experiment(:pie_or_cake).choose
+      assert experiment(:pie_or_cake).showing?(first)
+    end
+  end
+
+  def test_does_nothing_with_vanity_query_parameter_for_posts
+    first = experiment(:pie_or_cake).alternatives.first
+    post :index, :foo=>"bar", :_vanity=>"567"
+    assert_response :success
+    assert !experiment(:pie_or_cake).showing?(first)
+  end
+
   def teardown
     super
     UseVanityController.send(:filter_chain).clear