Add Pragma::Decorator::Association::Expander from pragma

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Added `Pragma::Decorator::Error`, which was previously in
   [pragma](https://github.com/pragmarb/pragma)
+- Added `Pragma::Decorator::Association::Expander`, which was previously in
+  [pragma](https://github.com/pragmarb/pragma)
 
 ### Changed
 

lib/pragma/decorator/association/expander.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module Pragma
+  module Decorator
+    module Association
+      module Expander
+        include Adaptor::Loader
+        register ActiveRecord, Poro
+      end
+    end
+  end
+end

lib/pragma/decorator/association/expander/active_record.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module Pragma
+  module Decorator
+    module Association
+      module Expander
+        class ActiveRecord < Base
+          class << self
+            def supports?(relation)
+              defined?(::ActiveRecord::Relation) && relation.is_a?(::ActiveRecord::Relation)
+            end
+          end
+
+          def include_associations(expands)
+            relation.includes(validate_associations(
+              relation.model,
+              destruct_associations(expands)
+            ))
+          end
+
+          private
+
+          def destruct_associations(expands)
+            associations = {}
+
+            expands.each do |expand|
+              expand.split('.').inject(associations) do |accumulator, association|
+                accumulator[association] ||= {}
+              end
+            end
+
+            associations
+          end
+
+          def validate_associations(model, associations)
+            Hash[associations.map do |(key, value)|
+              reflection = model.reflect_on_association(key.to_sym)
+              reflection ? [key, validate_associations(reflection.klass, value)] : [false, false]
+            end.select { |_, v| v }]
+          end
+        end
+      end
+    end
+  end
+end

lib/pragma/decorator/association/expander/base.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Pragma
+  module Decorator
+    module Association
+      module Expander
+        class Base
+          attr_reader :relation
+
+          class << self
+            def supports?(_relation)
+              fail NotImplementedError
+            end
+          end
+
+          def initialize(relation)
+            @relation = relation
+          end
+
+          def include_associations(_expands)
+            fail NotImplementedError
+          end
+        end
+      end
+    end
+  end
+end

lib/pragma/decorator/association/expander/poro.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Pragma
+  module Decorator
+    module Association
+      module Expander
+        class Poro < Base
+          class << self
+            def supports?(_relation)
+              true
+            end
+          end
+
+          def include_associations(_expands)
+            relation
+          end
+        end
+      end
+    end
+  end
+end