AbstractAdapter improved and added specs

lib/active_admin/object_mapper/abstract_adapter.rb

@@ -1,6 +1,37 @@
 module ActiveAdmin
   module ObjectMapper
     class AbstractAdapter
+
+      class << self
+
+        attr_accessor :adapters
+
+        def register(klass)
+          self.adapters ||= []
+          self.adapters << klass
+        end
+
+        def for(object_mapper, adapter_name, base)
+          klass = class_for(object_mapper, adapter_name)
+          adapters && adapters.include?(klass) or
+            raise NoAdapterFound.new("Adapter #{adapter_name} is not registered")
+          klass.new(base)
+        end
+
+        def class_for(object_mapper, adapter_name)
+          adapter_class = "#{adapter_name}_adapter"
+          class_name = "ActiveAdmin::ObjectMapper::#{object_mapper.to_s.classify}::#{adapter_class.classify}"
+          Object.const_defined?(class_name) or
+            raise NoAdapterFound.new("Class #{class_name} not found")
+          class_name.constantize
+        end
+
+        def inherited(klass)
+          ActiveAdmin::ObjectMapper::AbstractAdapter.register(klass)
+        end
+
+      end
+
       attr_accessor :base
 
       def initialize(base)

lib/active_admin/object_mapper/active_record.rb

@@ -4,20 +4,16 @@
 
 require 'active_admin/object_mapper/active_record/comments'
 
+require 'active_admin/object_mapper/active_record/adapters/form_builder_adapter'
+require 'active_admin/object_mapper/active_record/adapters/formtastic_addons_adapter'
+require 'active_admin/object_mapper/active_record/adapters/resource_extension_adapter'
+
 module ActiveAdmin
   module ObjectMapper
     module ActiveRecord
 
-      ADAPTERS = [ 'form_builder_adapter', 'formtastic_addons_adapter',
-        'resource_extension_adapter' ]
-
-      ADAPTERS.each do |adapter|
-        require "active_admin/object_mapper/active_record/adapters/#{adapter}"
-
-        klass = %[ActiveAdmin::ObjectMapper::ActiveRecord::#{adapter.classify}].constantize
-        define_singleton_method adapter do |base|
-          klass.new(base)
-        end
+      def self.adapter(name, base)
+        AbstractAdapter.for(:active_record, name, base)
       end
 
     end

spec/unit/object_mapper/abstract_adapter_spec.rb

@@ -0,0 +1,60 @@
+require 'rails_helper'
+
+describe ActiveAdmin::ObjectMapper::AbstractAdapter do
+
+  module ActiveAdmin::ObjectMapper::KnownOrm; class SimpleAdapter < ActiveAdmin::ObjectMapper::AbstractAdapter; end; end
+
+  let(:simple_adapter_class) { ActiveAdmin::ObjectMapper::KnownOrm::SimpleAdapter }
+
+  subject { ActiveAdmin::ObjectMapper::AbstractAdapter }
+
+  describe ".register" do
+    let(:adapter) { double }
+
+    after do
+      subject.adapters.delete(adapter)
+    end
+
+    it "registers an Adapter" do
+      subject.register adapter
+      expect(subject.adapters).to include(adapter)
+    end
+  end
+
+  describe ".for" do
+    context "When adapter is not found" do
+      it "rises a NoAdapterFound error" do
+        expect {
+          subject.for("unknown_orm", "simple", nil)
+        }.to raise_error ActiveAdmin::NoAdapterFound
+      end
+    end
+
+    context "When adapter is not registered" do
+      module ActiveAdmin::ObjectMapper::KnownOrm; class NotAdapter; end; end
+
+      it "rises a NoAdapterFound error" do
+        expect {
+          subject.for("known_orm", "not_adapter", nil)
+        }.to raise_error ActiveAdmin::NoAdapterFound
+      end
+    end
+
+    context "When adapter is registered" do
+      it "returns adapter" do
+        expect(subject.for("known_orm", "simple", nil)).to be_a(simple_adapter_class)
+      end
+    end
+  end
+
+  context "Adapter" do
+    let(:base_object) { double }
+    let(:simple_adapter) { subject.for("known_orm", "simple", base_object) }
+
+    it "delegates method calls to base object" do
+      expect(base_object).to receive(:method_of_object)
+      simple_adapter.method_of_object
+    end
+  end
+
+end