1 files changed, 94 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
new file mode 100644
index 0000000000..8734a0831e
--- /dev/null
+++ b/activerecord/lib/active_record/migration.rb
@@ -0,0 +1,94 @@
+module ActiveRecord
+  class IrreversibleMigration < ActiveRecordError
+  end
+  
+  class Migration
+    class << self
+      def up() end
+      def down() end
+
+      private
+        def method_missing(method, *arguments, &block)
+          ActiveRecord::Base.connection.send(method, *arguments, &block)
+        end
+    end
+  end
+
+  class Migrator
+    class << self
+      def up(migrations_path, target_version = nil)
+        new(:up, migrations_path, target_version).migrate
+      end
+      
+      def down(migrations_path, target_version = nil)
+        new(:down, migrations_path, target_version).migrate
+      end
+      
+      def current_version
+        Base.connection.select_one("SELECT version FROM schema_info")["version"].to_i
+      end
+    end
+    
+    def initialize(direction, migrations_path, target_version = nil)
+      @direction, @migrations_path, @target_version = direction, migrations_path, target_version
+    end
+
+    def current_version
+      self.class.current_version
+    end
+
+    def migrate
+      migration_classes do |version, migration_class|
+        Base.logger.info("Reached target version: #{@target_version}") and break if reached_target_version?(version)
+        next if irrelevant_migration?(version)
+
+        Base.logger.info "Migrating to #{migration_class} (#{version})"
+        migration_class.send(@direction)
+
+        set_schema_version(version)
+      end
+    end
+
+    private
+      def migration_classes
+        for migration_file in migration_files
+          load(migration_file)
+          version, name = migration_version_and_name(migration_file)
+          yield version, migration_class(name)
+        end
+      end
+    
+      def migration_files
+        files = Dir["#{@migrations_path}/[0-9]*_*.rb"]
+        down? ? files.reverse : files
+      end
+      
+      def migration_class(migration_name)
+        migration_name.camelize.constantize
+      end
+    
+      def migration_version_and_name(migration_file)
+        return *migration_file.scan(/([0-9]+)_([_a-z0-9]*).rb/).first
+      end
+      
+      def set_schema_version(version)
+        Base.connection.update("UPDATE schema_info SET version = #{down? ? version.to_i - 1 : version.to_i}")
+      end
+      
+      def up?
+        @direction == :up
+      end
+      
+      def down?
+        @direction == :down
+      end
+      
+      def reached_target_version?(version)
+        (up? && version.to_i - 1 == @target_version) || (down? && version.to_i == @target_version)
+      end
+      
+      def irrelevant_migration?(version)
+        (up? && version.to_i <= current_version) || (down? && version.to_i > current_version)
+      end
+  end
+end
+\ No newline at end of file