# HeartbeatFor

module HeartbeatFor
  
  def self.included(controller)
    controller.extend(ClassMethods)
  end
  
  module ClassMethods

    # updates a datetime column for a model every N minutes
    #
    # usage:
    #   (app/controllers/application.rb)
    #   heartbeat_for :current_user
    #
    #  or optionally specify the column name and interval:
    #   heartbeat_for :current_user, :last_seen, 5.minutes
    #
    # model_method:
    #   the method to return the model that you wish to check,
    #   e.g. :current_user
    #
    # heartbeat_method:
    #   the model's datetime column to store the heartbeat, 
    #   defaults to :last_activity
    #
    # interval:
    #   the interval in seconds to update the heartbeat,
    #   defaults to two minutes
    def heartbeat_for(model_method, heartbeat_method=:last_activity, interval=2.minutes)
      @_heartbeat_for_models ||= {}
      
      unless @_heartbeat_for_models.key?(model_method)
        @_heartbeat_for_models[model_method] = {
          :heartbeat => heartbeat_method,
          :interval => interval
        }
      end
      
      before_filter do |c|
        @_heartbeat_for_models.each do |model_method, props|
          model = c.send(model_method)
          # failsafe if model_method returns nil 
          next unless model && model.respond_to?(props[:heartbeat])
          
          now = Time.now.utc
          key = "#{model_method}_last_activity"
          if c.session[key].blank? || (now - c.session[key]) > props[:interval]
            c.session[key] = now
            model.send("#{props[:heartbeat]}=", now)
            model.save
          end
          
        end # each
      end # before_filter
    end # heartbeat_for
    
  end # ClassMethods
  
end