recommendations: filter out own uploads and favorites.

Filter out the user's own uploads and favorites from their
recommendations.

Note that in most cases a user's top-N recommendations will be things
they've already favorited. If a user has 10,000 favorites, most of their
top 10,000 recommendations will be their own favorites, so we have to
generate a little more than 10,000 recommendations to be sure they won't
all be filtered out.

In other words, the more favorites a user has, the more recommendations
we have to generate. The upper bound is clamped to 50,000 for
performance reasons. If a user has more favorites than this we may not
be able to find any recommendations for them.

app/controllers/recommended_posts_controller.rb

@@ -2,17 +2,10 @@ class RecommendedPostsController < ApplicationController
   respond_to :html, :json, :xml, :js
 
   def show
-    @max_recommendations = params.fetch(:max_recommendations, 100).to_i.clamp(0, 1000)
-
-    if params[:user_id].present?
-      @recs = RecommenderService.recommend_for_user(params[:user_id], @max_recommendations)
-    elsif params[:post_id].present?
-      @recs = RecommenderService.recommend_for_post(params[:post_id], @max_recommendations)
-    else
-      @recs = []
-    end
-
+    limit = params.fetch(:limit, 100).to_i.clamp(0, 200)
+    @recs = RecommenderService.search(params).take(limit)
     @posts = @recs.map { |rec| rec[:post] }
+
     respond_with(@recs)
   end
 end