* Refactored post history. Each post now has a single history record. This history record has multiple revisions, serialized as JSON in a text field.

app/models/post_history.rb

@@ -1,5 +1,60 @@
 class PostHistory < ActiveRecord::Base
   class Error < Exception ; end
+  
+  class Revision
+    attr_accessor :prev, :hash, :diff, :tag_array
+    
+    def initialize(hash)
+      @hash = hash
+      @diff = {}
+      @tag_array = Tag.scan_tags(@hash["tag_string"])
+    end
+    
+    def calculate_diff
+      if prev.nil?
+        diff[:add] = tag_array
+        diff[:del] = []
+        diff[:rating] = rating
+        diff[:source] = source
+        diff[:parent_id] = parent_id
+      else
+        diff[:del] = prev.tag_array - tag_array
+        diff[:add] = tag_array - prev.tag_array
+        
+        if prev.rating != rating
+          diff[:rating] = rating
+        end
+        
+        if prev.source != source
+          diff[:source] = source
+        end
+        
+        if prev.parent_id != parent_id
+          diff[:parent_id]= parent_id
+        end
+      end
+    end
+    
+    def rating
+      hash["rating"]
+    end
+    
+    def source
+      hash["source"]
+    end
+    
+    def parent_id
+      hash["parent_id"]
+    end
+    
+    def updated_at
+      hash["updated_at"]
+    end
+    
+    def updater_id
+      hash["user_id"]
+    end
+  end
 
   before_validation :initialize_revisions, :on => :create
   belongs_to :post
@@ -37,4 +92,19 @@ class PostHistory < ActiveRecord::Base
     write_attribute(:revisions, (revisions << revision).to_json)
     save
   end
+  
+  def each_revision(&block)
+    array = revisions.map {|x| Revision.new(x)}
+    link_revisions(array)
+    array.each {|x| x.calculate_diff}
+    array.each(&block)
+  end
+  
+  private
+    def link_revisions(array)
+      1.upto(array.size - 1) do |i|
+        array[i].prev = array[i - 1]
+      end
+    end
+  
 end