Added #active_users.

Guardfile

@@ -0,0 +1,6 @@
+guard 'rspec', :version => 2, :all_on_start => false,
+               :all_after_pass => false, :bundler => false,
+               :keep_failed => false do
+  watch(%r{^spec/.+_spec\.rb$})
+  watch(%r{^lib/(.+)\.rb$})     { |m| "spec/#{m[1]}_spec.rb" }
+end

README.md

@@ -26,11 +26,11 @@ In your ApplicationController:
       SessionTracker.new("user", $redis).track(session[:session_id])
     end
 
-In redis, do a union on the data for the last minute to get active users:
+Then to view the current state:
 
-    keys active_user*
-    sunion active_user_sessions_minute_12 active_user_sessions_minute_13 active_user_sessions_minute_14
+    SessionTracker.new("user", $redis).active_users
 
+If redis is accessible through $redis, you don't have to give it as an argument to SessionTracker.new.
 
 ## Contributing
 
@@ -42,6 +42,8 @@ In redis, do a union on the data for the last minute to get active users:
 
 ## Credits and license
 
+Inspired by [http://www.lukemelia.com/blog/archives/2010/01/17/redis-in-practice-whos-online/](http://www.lukemelia.com/blog/archives/2010/01/17/redis-in-practice-whos-online/).
+
 By [Joakim Kolsjö](https://github.com/joakimk) under the MIT license:
 
 >  Copyright (c) 2012 Joakim Kolsjö

lib/session_tracker.rb

@@ -18,7 +18,16 @@ def track(id, time = Time.now)
     # so we don't want to raise errors just because redis is down for a few seconds.
   end
 
+  def active_users(time = Time.now)
+    @redis.sunion(*keys_for_last_3_minutes(time)).size
+  end
+
   private
+
+  def keys_for_last_3_minutes(time)
+    times = 0.upto(2).map { |n| time - (n * 60) }
+    times.map { |t| key_for(t) }
+  end
 
   def key_for(time)
     "active_#{@type}_sessions_minute_#{time.strftime("%M")}"

spec/session_tracker_spec.rb

@@ -39,3 +39,19 @@
   end
 
 end
+
+describe SessionTracker, "active_users" do
+
+  let(:redis) { mock.as_null_object }
+
+  it "should do a union on the last 3 minutes to get a active user count" do
+    time = Time.parse("13:09")
+    redis.should_receive(:sunion).with("active_customer_sessions_minute_09",
+                                       "active_customer_sessions_minute_08",
+                                       "active_customer_sessions_minute_07").
+                                       and_return([ mock, mock ])
+
+    SessionTracker.new("customer", redis).active_users(time).should == 2
+  end
+
+end