1 files changed, 116 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/middleware/stack.rb b/actionpack/lib/action_dispatch/middleware/stack.rb
new file mode 100644
index 0000000000..b82f8aa3a3
--- /dev/null
+++ b/actionpack/lib/action_dispatch/middleware/stack.rb
@@ -0,0 +1,116 @@
+# frozen_string_literal: true
+
+require "active_support/inflector/methods"
+require "active_support/dependencies"
+
+module ActionDispatch
+  class MiddlewareStack
+    class Middleware
+      attr_reader :args, :block, :klass
+
+      def initialize(klass, args, block)
+        @klass = klass
+        @args  = args
+        @block = block
+      end
+
+      def name; klass.name; end
+
+      def ==(middleware)
+        case middleware
+        when Middleware
+          klass == middleware.klass
+        when Class
+          klass == middleware
+        end
+      end
+
+      def inspect
+        if klass.is_a?(Class)
+          klass.to_s
+        else
+          klass.class.to_s
+        end
+      end
+
+      def build(app)
+        klass.new(app, *args, &block)
+      end
+    end
+
+    include Enumerable
+
+    attr_accessor :middlewares
+
+    def initialize(*args)
+      @middlewares = []
+      yield(self) if block_given?
+    end
+
+    def each
+      @middlewares.each { |x| yield x }
+    end
+
+    def size
+      middlewares.size
+    end
+
+    def last
+      middlewares.last
+    end
+
+    def [](i)
+      middlewares[i]
+    end
+
+    def unshift(klass, *args, &block)
+      middlewares.unshift(build_middleware(klass, args, block))
+    end
+
+    def initialize_copy(other)
+      self.middlewares = other.middlewares.dup
+    end
+
+    def insert(index, klass, *args, &block)
+      index = assert_index(index, :before)
+      middlewares.insert(index, build_middleware(klass, args, block))
+    end
+
+    alias_method :insert_before, :insert
+
+    def insert_after(index, *args, &block)
+      index = assert_index(index, :after)
+      insert(index + 1, *args, &block)
+    end
+
+    def swap(target, *args, &block)
+      index = assert_index(target, :before)
+      insert(index, *args, &block)
+      middlewares.delete_at(index + 1)
+    end
+
+    def delete(target)
+      middlewares.delete_if { |m| m.klass == target }
+    end
+
+    def use(klass, *args, &block)
+      middlewares.push(build_middleware(klass, args, block))
+    end
+
+    def build(app = Proc.new)
+      middlewares.freeze.reverse.inject(app) { |a, e| e.build(a) }
+    end
+
+    private
+
+      def assert_index(index, where)
+        i = index.is_a?(Integer) ? index : middlewares.index { |m| m.klass == index }
+        raise "No such middleware to insert #{where}: #{index.inspect}" unless i
+        i
+      end
+
+      def build_middleware(klass, args, block)
+        Middleware.new(klass, args, block)
+      end
+  end
+end