Handlers can be added with a priority

lib/new_post_manager.rb

@@ -11,12 +11,21 @@ class NewPostManager
 
   attr_reader :user, :args
 
-  def self.handlers
-    @handlers ||= Set.new
+  def self.sorted_handlers
+    @sorted_handlers ||= clear_handlers!
   end
 
-  def self.add_handler(&block)
-    handlers << block
+  def self.handlers
+    sorted_handlers.map {|h| h[:proc]}
+  end
+
+  def self.clear_handlers!
+    @sorted_handlers = [{ priority: 0, proc: method(:default_handler) }]
+  end
+
+  def self.add_handler(priority=0, &block)
+    sorted_handlers << { priority: priority, proc: block }
+    @sorted_handlers.sort_by! {|h| -h[:priority]}
   end
 
   def self.default_handler(manager)
@@ -32,8 +41,6 @@ class NewPostManager
     handlers.size > 1
   end
 
-  add_handler {|manager| default_handler(manager) }
-
   def initialize(user, args)
     @user = user
     @args = args.delete_if {|_, v| v.nil?}

spec/components/new_post_manager_spec.rb

@@ -56,6 +56,34 @@ describe NewPostManager do
     end
   end
 
+  context "extensibility priority" do
+
+    after do
+      NewPostManager.clear_handlers!
+    end
+
+    let(:default_handler) { NewPostManager.method(:default_handler) }
+
+    it "adds in order by default" do
+      handler = ->{ nil }
+
+      NewPostManager.add_handler(&handler)
+      expect(NewPostManager.handlers).to eq([default_handler, handler])
+    end
+
+    it "can be added in high priority" do
+      a = ->{ nil }
+      b = ->{ nil }
+      c = ->{ nil }
+
+      NewPostManager.add_handler(100, &a)
+      NewPostManager.add_handler(50, &b)
+      NewPostManager.add_handler(101, &c)
+      expect(NewPostManager.handlers).to eq([c, a, b, default_handler])
+    end
+
+  end
+
   context "extensibility" do
 
     before do
@@ -78,8 +106,7 @@ describe NewPostManager do
     end
 
     after do
-      NewPostManager.handlers.delete(@counter_handler)
-      NewPostManager.handlers.delete(@queue_handler)
+      NewPostManager.clear_handlers!
     end
 
     it "has a queue enabled" do