gistfile1.rb

##lib/targeting_algorithm_manager.rb
class TargetingAlgorithmManager

  def self.method_missing(name, *args, &blk)
    debugger
    callbacks = ["before_validation","after_validation","before_save","before_create","after_create","after_save"]
    allowed_prefixes = callbacks#&other_prefixes&others&still_more
    if name.to_s.partially_included_in?(callbacks)
      self.send("#{name.to_s}_#{args[0].class.to_s.underscore}", args[0])
    elsif !name.to_s.partially_included_in?(allowed_prefixes)
      raise NoMethodError
    end
  end
end


##models/click.rb


class Click < ActiveRecord::Base

  db_magic :slaves => DB_READ_SLAVES

  after_create :decrement_campaign_quantity_remaining!
  after_create :algorithm_after_create
  after_create :check_campaign_daily_limit!

  validates_numericality_of :ad_id, :allow_nil => false
  validates_numericality_of :app_id, :allow_nil => false
  validates_numericality_of :impression_id, :allow_nil => false
  validates_numericality_of :user_id, :allow_nil => false
  validates_length_of :user_agent, :allow_blank => true, :maximum => 255

  belongs_to :ad
  belongs_to :app
  delegate   :campaign, :campaign=, :to => :ad
  belongs_to :impression
  belongs_to :user

  # self_serve clicks currently cost $1/each globally
  def self.cost(quantity = 1, discount_multiplier = 1)
    cost_per_unit = 100
    quantity * cost_per_unit * discount_multiplier
  end

protected

  # Callback to decrement our campaign's clicks counter after create
  # Currently only applies to clicks -- impressions are tracked via infrequent cronjobs
  def decrement_campaign_quantity_remaining!
    campaign.decrement_quantity_remaining!
  end

  # Let our campaign know we had another click, and thus potentially reached quota
  # FIXME redundant with decrement_campaign_quantity_remaining ???
  def check_campaign_daily_limit!
    campaign.check_daily_limit!
  end

  # Create ClickTag records for the subset of tags common to both our user & ad
  # FIXME this is duplicated in several models: Click, Retweet, Reply, Favorite, Friendship
  def algorithm_after_create
    TargetingAlgorithmManager.source(impression).after_create(self)
  end

end

##lib/targeting_algorithms/alpha_20110110155619.rb

class TargetingAlgorithmManager::Alpha20110110155619 < TargetingAlgorithmManager
  def after_create_click(click)
    do_stuff
  end
end