stub in preview for bulk revert

app/logical/bulk_revert.rb

@@ -0,0 +1,41 @@
+class BulkRevert
+  attr_reader :constraints
+
+  def initialize(constraints)
+    @constraints = constraints
+  end
+
+  def preview
+    @_preview ||= find_post_versions
+  end
+
+  def find_post_versions
+    q = PostVersion.where("true")
+
+    if constraints[:user_name]
+      constraints[:user_id] = User.find_by_name(constraints[:user_name]).try(:id)
+    end
+
+    if constraints[:user_id]
+      q = q.where("post_versions.updater_id = ?", constraints[:user_id])
+
+      if constraints[:added_tags] || constraints[:removed_tags]
+        hash = CityHash.hash64("#{constraints[:added_tags]} #{constraints{removed_tags}}").to_s(36)
+        sub_ids = Cache.get("br/fpv/#{hash}", 300) do
+          sub_ids = GoogleBigQuery::PostVersion.new.find(constraints[:user_id], constraints[:added_tags], constraints[:removed_tags])
+        end
+        q = q.where("post_versions.id in (?)", sub_ids)
+      end
+    end
+
+    if constraints[:min_version_id].present?
+      q = q.where("post_versions.id >= ?", constraints[:min_version_id])
+    end
+
+    if constraints[:max_version_id].present?
+      q = q.where("post_versions.id <= ?", constraints[:max_version_id])
+    end
+
+    q
+  end
+end