eventstore: SortedMerge() helper for combining results from different eventstores.

eventstore/combine.go

@@ -0,0 +1,61 @@
+package eventstore
+
+import (
+	"iter"
+
+	"fiatjaf.com/nostr"
+)
+
+func SortedMerge(it1, it2 iter.Seq[nostr.Event]) iter.Seq[nostr.Event] {
+	next1, done1 := iter.Pull(it1)
+	next2, done2 := iter.Pull(it2)
+
+	return func(yield func(nostr.Event) bool) {
+		defer done1()
+		defer done2()
+
+		evt1, ok1 := next1()
+		evt2, ok2 := next2()
+
+	both:
+		if ok1 && ok2 {
+			if evt2.CreatedAt > evt1.CreatedAt {
+				if !yield(evt2) {
+					return
+				}
+				evt2, ok2 = next2()
+				goto both
+			} else {
+				if !yield(evt1) {
+					return
+				}
+				evt1, ok1 = next1()
+				goto both
+			}
+		}
+
+		if !ok2 {
+		only1:
+			if ok1 {
+				if !yield(evt1) {
+					return
+				}
+				evt1, ok1 = next1()
+				goto only1
+			}
+		}
+
+		if !ok1 {
+		only2:
+			if ok2 {
+				if !yield(evt2) {
+					return
+				}
+				evt2, ok2 = next2()
+				goto only2
+			}
+		}
+
+		return
+	}
+}