nip45: hyperlolog small fixes and improvements. support deterministic offset for hardcoded set of queries.

nip45/hll_filter.go

@@ -0,0 +1,49 @@
+package nip45
+
+import (
+	"strconv"
+
+	"github.com/nbd-wtf/go-nostr"
+)
+
+// HyperLogLogEventPubkeyOffsetForFilter returns the deterministic pubkey offset that will be used
+// when computing hyperloglogs in the context of a specific filter.
+//
+// It returns -1 when the filter is not eligible for hyperloglog calculation.
+func HyperLogLogEventPubkeyOffsetForFilter(filter nostr.Filter) int {
+	if filter.IDs != nil || filter.Since != nil || filter.Until != nil || filter.Authors != nil ||
+		len(filter.Kinds) != 1 || filter.Search != "" || len(filter.Tags) != 1 {
+		// obvious cases in which we won't bother to do hyperloglog stuff
+		return -1
+	}
+
+	// only serve the cases explicitly defined by the NIP:
+	if pTags, ok := filter.Tags["p"]; ok {
+		//
+		// follower counts:
+		if filter.Kinds[0] == 3 && len(pTags) == 1 {
+			// 32th nibble of "p" tag
+			p, err := strconv.ParseInt(pTags[0][32:33], 16, 64)
+			if err != nil {
+				return -1
+			}
+			return int(p + 8)
+		}
+	} else if eTags, ok := filter.Tags["e"]; ok {
+		if len(eTags) == 1 {
+			//
+			// reaction counts:
+			if filter.Kinds[0] == 7 {
+				// 32th nibble of "e" tag
+				p, err := strconv.ParseInt(eTags[0][32:33], 16, 64)
+				if err != nil {
+					return -1
+				}
+				return int(p + 8)
+			}
+		}
+	}
+
+	// everything else is false at least for now
+	return -1
+}