1 files changed, 89 insertions, 0 deletions
diff --git a/railties/lib/rails/initializable.rb b/railties/lib/rails/initializable.rb
new file mode 100644
index 0000000000..1a0b6d1e1a
--- /dev/null
+++ b/railties/lib/rails/initializable.rb
@@ -0,0 +1,89 @@
+require 'tsort'
+
+module Rails
+  module Initializable
+    def self.included(base) #:nodoc:
+      base.extend ClassMethods
+    end
+
+    class Initializer
+      attr_reader :name, :block
+
+      def initialize(name, context, options, &block)
+        options[:group] ||= :default
+        @name, @context, @options, @block = name, context, options, block
+      end
+
+      def before
+        @options[:before]
+      end
+
+      def after
+        @options[:after]
+      end
+
+      def belongs_to?(group)
+        @options[:group] == group || @options[:group] == :all
+      end
+
+      def run(*args)
+        @context.instance_exec(*args, &block)
+      end
+
+      def bind(context)
+        return self if @context
+        Initializer.new(@name, context, @options, &block)
+      end
+    end
+
+    class Collection < Array
+      include TSort
+
+      alias :tsort_each_node :each
+      def tsort_each_child(initializer, &block)
+        select { |i| i.before == initializer.name || i.name == initializer.after }.each(&block)
+      end
+
+      def +(other)
+        Collection.new(to_a + other.to_a)
+      end
+    end
+
+    def run_initializers(group=:default, *args)
+      return if instance_variable_defined?(:@ran)
+      initializers.tsort_each do |initializer|
+        initializer.run(*args) if initializer.belongs_to?(group)
+      end
+      @ran = true
+    end
+
+    def initializers
+      @initializers ||= self.class.initializers_for(self)
+    end
+
+    module ClassMethods
+      def initializers
+        @initializers ||= Collection.new
+      end
+
+      def initializers_chain
+        initializers = Collection.new
+        ancestors.reverse_each do |klass|
+          next unless klass.respond_to?(:initializers)
+          initializers = initializers + klass.initializers
+        end
+        initializers
+      end
+
+      def initializers_for(binding)
+        Collection.new(initializers_chain.map { |i| i.bind(binding) })
+      end
+
+      def initializer(name, opts = {}, &blk)
+        raise ArgumentError, "A block must be passed when defining an initializer" unless blk
+        opts[:after] ||= initializers.last.name unless initializers.empty? || initializers.find { |i| i.name == opts[:before] }
+        initializers << Initializer.new(name, nil, opts, &blk)
+      end
+    end
+  end
+end