initial polymorphic input support

lib/plutonium/core/fields/inputs/factory.rb

@@ -9,6 +9,7 @@ class Factory
 
           map_type :has_one, to: Plutonium::Core::Fields::Inputs::NoopInput
           map_type :belongs_to, to: Plutonium::Core::Fields::Inputs::BelongsToAssociationInput
+          map_type :polymorphic_belongs_to, to: Plutonium::Core::Fields::Inputs::PolymorphicBelongsToAssociationInput
           map_type :has_many, to: Plutonium::Core::Fields::Inputs::HasManyAssociationInput
           map_type :attachment, to: Plutonium::Core::Fields::Inputs::AttachmentInput
           map_type :datetime, :date, :time, to: Plutonium::Core::Fields::Inputs::DateTimeInput

lib/plutonium/core/fields/inputs/polymorphic_belongs_to_association_input.rb

@@ -0,0 +1,47 @@
+module Plutonium
+  module Core
+    module Fields
+      module Inputs
+        class PolymorphicBelongsToAssociationInput < SimpleFormAssociationInput
+          def render(f, record, **opts)
+            opts = options.deep_merge opts
+            f.input param, **opts
+          end
+
+          private
+
+          def param
+            :"#{reflection.name}_sgid"
+          end
+
+          def input_options
+            {
+              as: :grouped_select,
+              label: reflection.name.to_s.humanize,
+              collection: associated_classes.map { |klass|
+                            [klass.name, klass.all]
+                          }.to_h,
+              group_label_method: :first,
+              group_method: :last, include_blank: "Select One"
+            }
+          end
+
+          def associated_classes
+            Rails.application.eager_load! unless Rails.application.config.eager_load
+
+            associated_classes = []
+            ActiveRecord::Base.descendants.each do |model|
+              next unless model.table_exists?
+              model.reflect_on_all_associations(:has_many).each do |association|
+                if association.options[:as] == reflection.name
+                  associated_classes << model.name
+                end
+              end
+            end
+            associated_classes
+          end
+        end
+      end
+    end
+  end
+end