1 files changed, 90 insertions, 0 deletions
diff --git a/app/serializers/activity_pub/activity_streams_serializer.rb b/app/serializers/activity_pub/activity_streams_serializer.rb
new file mode 100644
index 00000000000..39caa4a6d10
--- /dev/null
+++ b/app/serializers/activity_pub/activity_streams_serializer.rb
@@ -0,0 +1,90 @@
+# frozen_string_literal: true
+
+module ActivityPub
+  class ActivityStreamsSerializer < ::BaseSerializer
+    MissingIdentifierError = Class.new(StandardError)
+    MissingTypeError = Class.new(StandardError)
+    MissingOutboxError = Class.new(StandardError)
+
+    alias_method :base_represent, :represent
+
+    def represent(resource, opts = {}, entity_class = nil)
+      response = if respond_to?(:paginated?) && paginated?
+                   represent_paginated(resource, opts, entity_class)
+                 else
+                   represent_whole(resource, opts, entity_class)
+                 end
+
+      validate_response(HashWithIndifferentAccess.new(response))
+    end
+
+    private
+
+    def validate_response(response)
+      unless response[:id].present?
+        raise MissingIdentifierError, "The serializer does not provide the mandatory 'id' field."
+      end
+
+      unless response[:type].present?
+        raise MissingTypeError, "The serializer does not provide the mandatory 'type' field."
+      end
+
+      response
+    end
+
+    def represent_whole(resource, opts, entity_class)
+      raise MissingOutboxError, 'Please provide an :outbox option for this actor' unless opts[:outbox].present?
+
+      serialized = base_represent(resource, opts, entity_class)
+
+      {
+        :@context => "https://www.w3.org/ns/activitystreams",
+        inbox: opts[:inbox],
+        outbox: opts[:outbox]
+      }.merge(serialized)
+    end
+
+    def represent_paginated(resources, opts, entity_class)
+      if paginator.params['page'].present?
+        represent_page(resources, resources.current_page, opts, entity_class)
+      else
+        represent_pagination_index(resources)
+      end
+    end
+
+    def represent_page(resources, page, opts, entity_class)
+      opts[:page] = page
+      serialized = base_represent(resources, opts, entity_class)
+
+      {
+        :@context => 'https://www.w3.org/ns/activitystreams',
+        type: 'OrderedCollectionPage',
+        id: collection_url(page),
+        prev: page > 1 ? collection_url(page - 1) : nil,
+        next: page < resources.total_pages ? collection_url(page + 1) : nil,
+        partOf: collection_url,
+        orderedItems: serialized
+      }
+    end
+
+    def represent_pagination_index(resources)
+      {
+        :@context => 'https://www.w3.org/ns/activitystreams',
+        type: 'OrderedCollection',
+        id: collection_url,
+        totalItems: resources.total_count,
+        first: collection_url(1),
+        last: collection_url(resources.total_pages)
+      }
+    end
+
+    def collection_url(page = nil)
+      uri = URI.parse(paginator.request.url)
+      uri.query ||= ""
+      parts = uri.query.split('&').reject { |part| part =~ /^page=/ }
+      parts << "page=#{page}" if page
+      uri.query = parts.join('&')
+      uri.to_s.sub(/\?$/, '')
+    end
+  end
+end