Add rake task for changing timestamps to UTC

Rails 2 used local times, Rails 3 assumes by default times are stored in UTC.
This rake task changes the timestamps in the database to UTC.

doc/CHANGELOG.md

@@ -47,6 +47,7 @@ See doc/COPYRIGHT.rdoc for more details.
 * `#2596` [Roadmap] Closed tickets are not striked out
 * `#2597` [Roadmap] Missing english/german closed percentage label 
 * `#2604` [Migration] Attachable journals incorrect
+* Add rake task for changing timestamps in the database to UTC
 
 ## 3.0.0pre23
 

lib/tasks/migrate_timezones.rake

@@ -0,0 +1,51 @@
+#-- encoding: UTF-8
+#-- copyright
+# OpenProject is a project management system.
+#
+# Copyright (C) 2012-2013 the OpenProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# See doc/COPYRIGHT.rdoc for more details.
+#++
+
+namespace :migrations do
+  desc "Use FROM environment variable to define a timezone to migrate from.
+  Examples: LOCAL
+            'Europe/Berlin'"
+  task :change_timestamps_to_utc => :environment do |task|
+    def postgres?
+      ActiveRecord::Base.connection.instance_values["config"][:adapter] == "postgresql"
+    end
+
+    raise "Error: Adapting Timestamps from system timezone to UTC is only supported for " +
+          "postgres yet." unless postgres?
+
+    old_timezone = ActiveRecord::Base.connection.select_all(
+                    "SELECT current_setting('timezone') AS timezone").first['timezone']
+
+    from_timezone = ENV['FROM'] || 'LOCAL'
+
+    begin
+      ActiveRecord::Base.connection.execute "SET TIME ZONE #{from_timezone}"
+
+      queries = ActiveRecord::Base.connection.select_all <<-SQL
+        select 'UPDATE ' || table_name || ' SET ' || column_name || ' = ' || column_name || '::timestamptz at time zone ''utc'';'
+        from information_schema.columns
+        where table_schema='public'
+        and data_type like 'timestamp without time zone'
+      SQL
+
+      mem = queries.inject([]) do |mem, entry|
+        mem << entry.values.first
+      end
+
+      ActiveRecord::Base.connection.execute mem.join("\n")
+
+    ensure
+      ActiveRecord::Base.connection.execute "SET TIME ZONE '#{old_timezone}'"
+    end
+  end
+
+end