online.rb

class Online
	include MongoMapper::Document
	
	key :ip, String, :required => true
	key :page, String, :required => true
	key :time, Integer, :required => true
	
	before_save :delete_old_entries # Automatically delete old entries before saving a new one
	
	def add_online(ip, page)
		# Add/update new online user
		person = Online.first(:ip => ip)
		if person.to_s.empty? # Is this IP already on the DB?
			online = Online.create({
				:ip => ip,
				:page => page,
				:time => Time.new.to_i
			})
			online.save
		else
			person.page = page # Update :page to the currently viewed webpage
			person.time = Time.new.to_i # Update :time for the current entry
			person.save
		end
	end
	
	def count_online(opts={})
		page = opts[:page] || ""
		if page.empty? # Count every user online
			people = Online.count()
		else # Count only users on X page
			people = Online.count({:page => page})
		end
		return people # returns Integer
	end
	
	private
	def delete_old_entries
		time = Time.new.to_i
		limit = 15 # Seconds to keep old entries alive
		online = Online.delete_all(:time => {"$lt" => time-limit})
	end
end

# On each page
online = Online.new
online.add_online("255.255.255.255", "/")

# Count only users on the site
online.count_online

# Count online users on "/profile/admin"
online.count_online({:page => "/profile/admin"})