chore: move the go code into a subfolder

apps/api/internal/eventstore/read_model.go

@@ -0,0 +1,55 @@
+package eventstore
+
+import (
+	"time"
+
+	"github.com/shopspring/decimal"
+)
+
+// ReadModel is the minimum representation of a read model.
+// It implements a basic reducer
+// it might be saved in a database or in memory
+type ReadModel struct {
+	AggregateID       string          `json:"-"`
+	ProcessedSequence uint64          `json:"-"`
+	CreationDate      time.Time       `json:"-"`
+	ChangeDate        time.Time       `json:"-"`
+	Events            []Event         `json:"-"`
+	ResourceOwner     string          `json:"-"`
+	InstanceID        string          `json:"-"`
+	Position          decimal.Decimal `json:"-"`
+}
+
+// AppendEvents adds all the events to the read model.
+// The function doesn't compute the new state of the read model
+func (rm *ReadModel) AppendEvents(events ...Event) {
+	rm.Events = append(rm.Events, events...)
+}
+
+// Reduce is the basic implementation of reducer
+// If this function is extended the extending function should be the last step
+func (rm *ReadModel) Reduce() error {
+	if len(rm.Events) == 0 {
+		return nil
+	}
+
+	if rm.AggregateID == "" {
+		rm.AggregateID = rm.Events[0].Aggregate().ID
+	}
+	if rm.ResourceOwner == "" {
+		rm.ResourceOwner = rm.Events[0].Aggregate().ResourceOwner
+	}
+	if rm.InstanceID == "" {
+		rm.InstanceID = rm.Events[0].Aggregate().InstanceID
+	}
+
+	if rm.CreationDate.IsZero() {
+		rm.CreationDate = rm.Events[0].CreatedAt()
+	}
+	rm.ChangeDate = rm.Events[len(rm.Events)-1].CreatedAt()
+	rm.ProcessedSequence = rm.Events[len(rm.Events)-1].Sequence()
+	rm.Position = rm.Events[len(rm.Events)-1].Position()
+	// all events processed and not needed anymore
+	rm.Events = rm.Events[0:0]
+	return nil
+}