added post mod details

app/logical/related_tag_calculator.rb

@@ -0,0 +1,33 @@
+class RelatedTagCalculator
+  def find_tags(tag, limit)
+    ActiveRecord::Base.connection.select_values_sql("SELECT tag_string FROM posts WHERE tag_index @@ to_tsquery('danbooru', ?) ORDER BY id DESC LIMIT ?", tag, limit)
+  end
+  
+  def calculate_from_sample(name, limit, category_constraint = nil)
+    counts = Hash.new {|h, k| h[k] = 0}
+    
+    find_tags(name, limit).each do |post|
+      if category_constraint
+        categories = Tag.categories_for(post.tag_array)
+        
+        post.tag_array.each do |tag|
+          if categories[tag] == category_constraint && tag != name
+            counts[tag] += 1
+          end
+        end
+      else
+        post.tag_array.each do |tag|
+          if tag != name
+            counts[tag] += 1
+          end
+        end
+      end
+    end
+    
+    counts
+  end
+  
+  def convert_hash_to_string(hash)
+    hash.to_a.sort_by {|x| -x[1]}.flatten.join(" ")
+  end
+end