group the "suggested topics" by category correctly.

in the past new topics were not prioritizing current category and
new topics in a category were not being inserted before other unread topics
in other categories

lib/suggested_topics_builder.rb

@@ -3,14 +3,15 @@ require_dependency 'topic_list'
 class SuggestedTopicsBuilder
 
   attr_reader :excluded_topic_ids
-  attr_reader :results
 
   def initialize(topic)
     @excluded_topic_ids = [topic.id]
+    @category_id = topic.category_id
     @results = []
   end
 
-  def add_results(results)
+
+  def add_results(results, priority=:low)
 
     # WARNING .blank? will execute an Active Record query
     return unless results
@@ -23,16 +24,46 @@ class SuggestedTopicsBuilder
     unless results.empty?
       # Keep track of the ids we've added
       @excluded_topic_ids.concat results.map {|r| r.id}
+      splice_results(results,priority)
+    end
+  end
+
+  def splice_results(results, priority)
+    if  @category_id &&
+        priority == :high &&
+        non_category_index = @results.index{|r| r.category_id != @category_id}
+
+      category_results, non_category_results = results.partition{|r| r.category_id == @category_id}
+
+      @results.insert non_category_index, *category_results
+      @results.concat non_category_results
+    else
       @results.concat results
     end
   end
 
+  def results
+    @results.first(SiteSetting.suggested_topics)
+  end
+
   def results_left
     SiteSetting.suggested_topics - @results.size
   end
 
   def full?
-    results_left == 0
+    results_left <= 0
+  end
+
+  def category_results_left
+    SiteSetting.suggested_topics - @results.count{|r| r.category_id == @category_id}
+  end
+
+  def category_full?
+    if @category_id
+
+    else
+      full?
+    end
   end
 
   def size