Add ValueObjectFactory

dapps/valuetransfers/packages/tangle/factory.go

+package tangle
+
+import (
+	"github.com/iotaledger/goshimmer/dapps/valuetransfers/packages/branchmanager"
+	"github.com/iotaledger/goshimmer/dapps/valuetransfers/packages/payload"
+	"github.com/iotaledger/goshimmer/dapps/valuetransfers/packages/tipmanager"
+	"github.com/iotaledger/goshimmer/dapps/valuetransfers/packages/transaction"
+	"github.com/iotaledger/hive.go/events"
+)
+
+type ValueObjectFactory struct {
+	branchManager *branchmanager.BranchManager
+	tipManager    *tipmanager.TipManager
+	Events        *ValueObjectFactoryEvents
+}
+
+func NewValueObjectFactory(branchManager *branchmanager.BranchManager, tipManager *tipmanager.TipManager) *ValueObjectFactory {
+	return &ValueObjectFactory{
+		branchManager: branchManager,
+		tipManager:    tipManager,
+		Events: &ValueObjectFactoryEvents{
+			ValueObjectConstructed: events.NewEvent(valueObjectConstructedEvent),
+		},
+	}
+}
+
+func (v *ValueObjectFactory) IssueTransaction(tx *transaction.Transaction) *payload.Payload {
+	// TODO: we need a way to get the currently liked branches. e.g. branchManager.LikedBranches()
+	parent1, parent2 := v.tipManager.Tips()
+
+	valueObject := payload.New(parent1, parent2, tx)
+	v.Events.ValueObjectConstructed.Trigger(valueObject)
+
+	return valueObject
+}
+
+// ValueObjectFactoryEvents represent events happening on a ValueObjectFactory.
+type ValueObjectFactoryEvents struct {
+	// Fired when a value object is built including tips.
+	ValueObjectConstructed *events.Event
+}
+
+func valueObjectConstructedEvent(handler interface{}, params ...interface{}) {
+	handler.(func(*transaction.Transaction))(params[0].(*transaction.Transaction))
+}