1 files changed, 49 insertions, 0 deletions
diff --git a/core/map.go b/core/map.go
new file mode 100644
index 0000000..c011e8d
--- /dev/null
+++ b/core/map.go
@@ -0,0 +1,49 @@
+package core
+
+import "fmt"
+
+// MapFunc is business logic for user implement
+type MapFunc[IN, OUT any] func(in IN) (OUT, error)
+
+type MapOperator[IN, OUT any] struct {
+	userFunc MapFunc[IN, OUT]
+}
+
+func NewMapFuncOperator[IN, OUT any](fn MapFunc[IN, OUT]) *MapOperator[IN, OUT] {
+	return &MapOperator[IN, OUT]{
+		userFunc: fn,
+	}
+}
+
+func (fo *MapOperator[IN, OUT]) Open() error {
+	return nil
+}
+
+func (fo *MapOperator[IN, OUT]) Process(record StreamRecord[IN], out Emitter[OUT]) error {
+	if record.Type != RecordData {
+		//	 watermark and barrier
+		return out.Emit(StreamRecord[OUT]{
+			Type:      record.Type,
+			Key:       record.Key,
+			Timestamp: record.Timestamp,
+			BarrierID: record.BarrierID,
+		})
+	}
+
+	outValue, err := fo.userFunc(record.Value)
+
+	if err != nil {
+		return fmt.Errorf("cannot process value: %v", record.Value)
+	}
+
+	return out.Emit(StreamRecord[OUT]{
+		Type:      RecordData,
+		Key:       record.Key,
+		Timestamp: record.Timestamp,
+		Value:     outValue,
+	})
+}
+
+func (fo *MapOperator[IN, OUT]) Close() error {
+	return nil
+}