Show conference changelog

Use load_and_authorize_resource in versions controlller
Add conference specifc route to revision history page
Users with role can view revision_history only for the versions they have access to
Handle versions where conference_id is not set (records before papertrail was introduced)

app/helpers/application_helper.rb

@@ -98,25 +98,6 @@ module ApplicationHelper
       .reverse.sub(',', ' dna ').reverse
   end
 
-  # Recieves a model_name and id
-  # Returns nil if model_name is invalid
-  # Returns object in its current state if its alive
-  # Otherwise Returns object state just before deletion
-  def current_or_last_object_state(model_name, id)
-    return nil unless id.present? && model_name.present?
-    begin
-      object = model_name.constantize.find_by(id: id)
-    rescue NameError
-      return nil
-    end
-
-    if object.nil?
-      object_last_version = PaperTrail::Version.where(item_type: model_name, item_id: id).last
-      object = object_last_version.reify if object_last_version
-    end
-    object
-  end
-
   def normalize_array_length(hashmap, length)
     hashmap.each do |_, value|
       if value.length < length

app/helpers/versions_helper.rb

@@ -2,8 +2,52 @@ module VersionsHelper
   ##
   # Groups functions related to change description
   ##
-  def link_if_alive(version, link_text, link_url)
-    version.item ? link_to(link_text, link_url) : link_text
+  def link_if_alive(version, link_text, link_url, conference)
+    version.item && conference ? link_to(link_text, link_url) : "#{link_text} with ID #{version.item_id}"
+  end
+
+  def link_to_conference(conference_id)
+    return 'deleted conference' if conference_id.nil?
+
+    conference = Conference.find_by(id: conference_id)
+    if conference
+      link_to conference.short_title,
+              edit_admin_conference_path(conference.short_title)
+    else
+      short_title = current_or_last_object_state('Conference', conference_id).try(:short_title) || ''
+      " #{short_title} with ID #{conference_id}"
+    end
+  end
+
+  def link_to_user(user_id)
+    return 'Someone (probably via the console)' unless user_id
+
+    user = User.find_by(id: user_id)
+    if user
+      link_to user.name, admin_user_path(id: user_id)
+    else
+      name = current_or_last_object_state('User', user_id).try(:name)
+      "#{name ? name : 'Unknown user'} with ID #{user_id}"
+    end
+  end
+
+  # Recieves a model_name and id
+  # Returns nil if model_name is invalid
+  # Returns object in its current state if its alive
+  # Otherwise Returns object state just before deletion
+  def current_or_last_object_state(model_name, id)
+    return nil unless id.present? && model_name.present?
+    begin
+      object = model_name.constantize.find_by(id: id)
+    rescue NameError
+      return nil
+    end
+
+    if object.nil?
+      object_last_version = PaperTrail::Version.where(item_type: model_name, item_id: id).last
+      object = object_last_version.reify if object_last_version
+    end
+    object
   end
 
   def subscription_change_description(version)