major refactor to accommodate feed

options.go

@@ -0,0 +1,24 @@
+package gubgub
+
+// TopicOptions holds common options for topics.
+type TopicOptions struct {
+	// onClose is called after the Topic is closed and all messages have been delivered.
+	onClose func()
+
+	// onSubscribe is called after a new subscriber is regitered.
+	onSubscribe func(count int)
+}
+
+type TopicOption func(*TopicOptions)
+
+func WithOnClose(fn func()) TopicOption {
+	return func(opts *TopicOptions) {
+		opts.onClose = fn
+	}
+}
+
+func WithOnSubscribe(fn func(count int)) TopicOption {
+	return func(opts *TopicOptions) {
+		opts.onSubscribe = fn
+	}
+}