expensive_way_to_query.rb

class ActivityCollator

  def self.for(user, filter, limit)
    new(user).list(filter, limit)
  end

  def initialize(user)
    @user = user
  end

  def list(filter, limit)
    # WARNING this wont scale, will need to move to a notification based approach at some point
    # The following code exposes the classic Twitter scaling problem
    # before that a hand crafted SQL statement might work too and it should probably be cached as well

    # Heres how this algo works
    # Theres a max of 14 items that fit on to the home page, so get 14 of each possible content type and then
    # throw away all but the latest 14

    result = []
    result << list_own_thoughts(limit) if filter.blank? or filter == "thoughts"
    result << list_comments_on_supported_items(limit) if filter.blank? or filter == "comments"
    result << list_actions_on_supported_thoughts(limit) if filter.blank? or filter == "actions"
    result << list_intents_on_supported_actions(limit) if filter.blank? or filter == "intents"
    result << list_stories_on_supported_actions(limit) if filter.blank? or filter == "stories"

    result << list_comments_on_my_items(limit) if filter.blank? or filter == "comments"
    result << list_actions_on_my_thoughts(limit) if filter.blank? or filter == "actions"
    result << list_intents_on_my_items(limit) if filter.blank? or filter == "intents"
    result << list_stories_on_my_items(limit) if filter.blank? or filter == "stories"

    result.flatten.uniq.sort_by(&:updated_at).reverse[0..limit]
  end

  private
  
    def list_own_thoughts(limit)
      @user.thoughts.all :limit => limit, :order => "updated_at desc"
    end
  
    def list_comments_on_supported_items(limit)
      ["Thought", "Action", "Feedback"].map do |type|
        Comment.all :limit => limit,
                    :order => "created_at desc",
                    :conditions => { :commentable_type => type, :commentable_id => @user.send("supported_#{type.downcase.pluralize}").map(&:id) }
      end.flatten
    end

    def list_actions_on_supported_thoughts(limit)
      Action.all :limit => limit,
                 :order => "updated_at desc",
                 :conditions => { :thought_id => @user.supported_thoughts.map(&:id) }
    end

    def list_intents_on_supported_actions(limit)
      Intent.all :limit => limit,
                 :order => "created_at desc",
                 :conditions => { :action_id => @user.supported_actions.map(&:id), :completed => false }
    end

    def list_stories_on_supported_actions(limit)
      Intent.all :limit => limit,
                 :order => "created_at desc",
                 :conditions => { :action_id => @user.supported_actions.map(&:id), :completed => true }
    end


    def list_comments_on_my_items(limit)
      ["Thought", "Action", "Feedback"].map do |type|
        Comment.all(:limit => limit,
                    :order => "created_at desc",
                    :conditions => { :commentable_type => type, :commentable_id => @user.send(type.downcase.pluralize).map(&:id) })
      end.flatten
    end

    def list_actions_on_my_thoughts(limit)
      Action.all :limit => limit,
                 :order => "created_at desc",
                 :conditions => { :thought_id => @user.thoughts.map(&:id) }
    end

    def list_intents_on_my_items(limit)
      Intent.all :limit => limit,
                 :order => "updated_at desc",
                 :conditions => { :action_id => @user.actions.map(&:id), :completed => false }
    end

    def list_stories_on_my_items(limit)
      Intent.all :limit => limit,
                 :order => "updated_at desc",
                 :conditions => { :action_id => @user.actions.map(&:id), :completed => true }
    end

end