feat: add typed callback handler

Signed-off-by: Christian Stewart <[email protected]>

directive/typed-callback-handler.go

@@ -0,0 +1,73 @@
+package directive
+
+// TypedCallbackHandler is a generic reference handler that uses function callbacks.
+//
+// Values with unknown type are optionally passed to the optional unknownTypeHandler.
+type TypedCallbackHandler[T ComparableValue] struct {
+	valCb     func(TypedAttachedValue[T])
+	removedCb func(TypedAttachedValue[T])
+	disposeCb func()
+
+	unknownTypeHandler ReferenceHandler
+}
+
+// NewTypedCallbackHandler wraps callback functions into a handler object.
+//
+// unknownTypeHandler can be nil
+func NewTypedCallbackHandler[T ComparableValue](
+	valCb func(TypedAttachedValue[T]),
+	removedCb func(TypedAttachedValue[T]),
+	disposeCb func(),
+	unknownTypeHandler ReferenceHandler,
+) ReferenceHandler {
+	return &TypedCallbackHandler[T]{
+		valCb:              valCb,
+		removedCb:          removedCb,
+		disposeCb:          disposeCb,
+		unknownTypeHandler: unknownTypeHandler,
+	}
+}
+
+// HandleValueAdded is called when a value is added to the directive.
+func (h *TypedCallbackHandler[T]) HandleValueAdded(
+	di Instance,
+	v AttachedValue,
+) {
+	val, ok := v.GetValue().(T)
+	if ok {
+		if h.valCb != nil {
+			h.valCb(NewTypedAttachedValue(v.GetValueID(), val))
+		}
+	} else if h.unknownTypeHandler != nil {
+		h.unknownTypeHandler.HandleValueAdded(di, v)
+	}
+}
+
+// HandleValueRemoved is called when a value is removed from the directive.
+func (h *TypedCallbackHandler[T]) HandleValueRemoved(
+	di Instance,
+	v AttachedValue,
+) {
+	val, ok := v.GetValue().(T)
+	if ok {
+		if h.removedCb != nil {
+			h.removedCb(NewTypedAttachedValue(v.GetValueID(), val))
+		}
+	} else if h.unknownTypeHandler != nil {
+		h.unknownTypeHandler.HandleValueRemoved(di, v)
+	}
+}
+
+// HandleInstanceDisposed is called when a directive instance is disposed.
+// This will occur if Close() is called on the directive instance.
+func (h *TypedCallbackHandler[T]) HandleInstanceDisposed(i Instance) {
+	if h.disposeCb != nil {
+		h.disposeCb()
+	}
+	if h.unknownTypeHandler != nil {
+		h.unknownTypeHandler.HandleInstanceDisposed(i)
+	}
+}
+
+// _ is a type assertion
+var _ ReferenceHandler = ((*TypedCallbackHandler[int])(nil))