Add ServiceTemplate.class_from_prov_type to hide the complexity of finding a ServiceTemplate class

app/models/service_template.rb

@@ -137,13 +137,31 @@ def self.create_catalog_item(options, auth_user)
   end
 
   def self.class_from_request_data(data)
-    request_type = data['prov_type']
-    if request_type.include?('generic_')
-      generic_type = request_type.split('generic_').last
-      "ServiceTemplate#{generic_type.camelize}".constantize
+    class_from_prov_type(data['prov_type'])
+  end
+
+  def self.class_from_prov_type(prov_type)
+    # This is the full list of acceptable values.  This allows us to check for
+    # class name validity before calling constantize.
+    allowed_class_names = descendants.collect(&:name)
+
+    raise ArgumentError, "Invalid prov_type '#{prov_type}'" unless all_catalog_item_types.key?(prov_type)
+
+    # If we are given a "generic" provision type then assume that the prov_type
+    # maps to a valid class otherwise it is invalid
+    #
+    # Non-generic provision types however are able to work with the base
+    # ServiceTemplate class and thus we cannot raise an exception in this case.
+    if prov_type.starts_with?("generic_")
+      generic_type = prov_type.split('generic_').last
+      class_name   = "ServiceTemplate#{generic_type.camelize}"
+      raise ArgumentError, "Invalid prov_type '#{prov_type}'" unless allowed_class_names.include?(class_name)
     else
-      ServiceTemplate
+      class_name = "ServiceTemplate#{prov_type.camelize}"
+      class_name = "ServiceTemplate" unless allowed_class_names.include?(class_name)
     end
+
+    class_name.constantize
   end
 
   def update_catalog_item(options, auth_user = nil)

spec/models/service_template_spec.rb

@@ -719,6 +719,40 @@
     end
   end
 
+  describe '.class_from_prov_type' do
+    it 'returns the correct generic type' do
+      template_class = ServiceTemplate.class_from_prov_type('generic_ansible_tower')
+
+      expect(template_class).to eq(ServiceTemplateAnsibleTower)
+    end
+
+    it 'raises an exception for an invalid generic type' do
+      expect { ServiceTemplate.class_from_prov_type('generic_invalid') }
+        .to raise_error(ArgumentError, /Invalid prov_type/)
+    end
+
+    it 'raises an exception when missing a ServiceTemplate sub-class for a valid prov_type' do
+      expect(described_class).to receive(:all_catalog_item_types).and_return("generic_invalid" => "Invalid but somehow kind of valid")
+      expect { ServiceTemplate.class_from_prov_type('generic_invalid') }
+        .to raise_error(ArgumentError, /Invalid prov_type/)
+    end
+
+    it 'returns the correct non-generic type mapping to ::ServiceTemplate' do
+      template_class = ServiceTemplate.class_from_prov_type('amazon')
+
+      expect(template_class).to eq(ServiceTemplate)
+    end
+
+    it 'returns the correct non-generic type when mapping to a ServiceTemplate subclass' do
+      expect(ServiceTemplate.class_from_prov_type("awx")).to eq(ServiceTemplateAwx)
+    end
+
+    it 'raises an exception for an invalid non-generic type' do
+      expect { ServiceTemplate.class_from_prov_type('invalid') }
+        .to raise_error(ArgumentError, /Invalid prov_type/)
+    end
+  end
+
   let(:user) { FactoryBot.create(:user_with_group) }
   let(:ra1) { FactoryBot.create(:resource_action, :action => 'Provision') }
   let(:ra2) { FactoryBot.create(:resource_action, :action => 'Retirement') }