Change bus

models/utils/change_bus.go

@@ -0,0 +1,60 @@
+package utils
+
+import (
+	"sync"
+
+	"cloud.o-forge.io/core/oc-lib/tools"
+)
+
+// ChangeEvent is fired whenever a DB object is created, updated or deleted
+// within this process. Deleted=true means the object was removed; Object is
+// the last known snapshot before deletion.
+type ChangeEvent struct {
+	DataType tools.DataType
+	ID       string
+	Object   ShallowDBObject // nil only when the load after the write failed
+	Deleted  bool
+}
+
+var (
+	changeBusMu sync.RWMutex
+	changeBus   = map[tools.DataType][]chan ChangeEvent{}
+)
+
+// SubscribeChanges returns a channel that receives ChangeEvents for dt
+// whenever an object of that type is written or deleted in this process.
+// Call the returned cancel function to unsubscribe; after that the channel
+// will no longer receive events (it is not closed — use a context to stop
+// reading).
+func SubscribeChanges(dt tools.DataType) (<-chan ChangeEvent, func()) {
+	ch := make(chan ChangeEvent, 32)
+	changeBusMu.Lock()
+	changeBus[dt] = append(changeBus[dt], ch)
+	changeBusMu.Unlock()
+	return ch, func() {
+		changeBusMu.Lock()
+		subs := changeBus[dt]
+		for i, c := range subs {
+			if c == ch {
+				changeBus[dt] = append(subs[:i], subs[i+1:]...)
+				break
+			}
+		}
+		changeBusMu.Unlock()
+	}
+}
+
+// NotifyChange broadcasts a ChangeEvent to all current subscribers for dt.
+// Non-blocking: events are dropped for subscribers whose buffer is full.
+func NotifyChange(dt tools.DataType, id string, obj ShallowDBObject, deleted bool) {
+	changeBusMu.RLock()
+	subs := changeBus[dt]
+	changeBusMu.RUnlock()
+	evt := ChangeEvent{DataType: dt, ID: id, Object: obj, Deleted: deleted}
+	for _, ch := range subs {
+		select {
+		case ch <- evt:
+		default:
+		}
+	}
+}