feat: add KeyByOperator and wordCounter for stateful processing

1 files changed, 32 insertions, 0 deletions

diff --git a/core/operator/keyby.go b/core/operator/keyby.go
new file mode 100644
index 0000000..1296df0
--- /dev/null
+++ b/core/operator/keyby.go
@@ -0,0 +1,32 @@
+package operator
+
+import (
+	"context"
+	"goflink/core"
+)
+
+type KeySelector[IN any] func(in IN) string
+type KeyByOperator[IN any] struct {
+	selector KeySelector[IN]
+}
+
+func NewKeyByOperator[IN any](selector KeySelector[IN]) *KeyByOperator[IN] {
+	return &KeyByOperator[IN]{selector: selector}
+}
+
+func (k *KeyByOperator[IN]) Open(ctx context.Context) error {
+	return nil
+}
+
+func (k *KeyByOperator[IN]) Process(ctx context.Context, record core.StreamRecord[IN], out Emitter[IN]) error {
+	if record.Type != core.RecordData {
+		return out.Emit(ctx, record)
+	}
+
+	record.Key = k.selector(record.Value)
+	return out.Emit(ctx, record)
+}
+
+func (k *KeyByOperator[IN]) Close(ctx context.Context) error {
+	return nil
+}