Add kinds module to classify events by kind

src/kinds.ts

@@ -0,0 +1,40 @@
+/** Events are **regular**, which means they're all expected to be stored by relays. */
+function isRegularKind(kind: number) {
+  return 1000 <= kind && kind < 10000;
+}
+
+/** Events are **replaceable**, which means that, for each combination of `pubkey` and `kind`, only the latest event is expected to (SHOULD) be stored by relays, older versions are expected to be discarded. */
+function isReplaceableKind(kind: number) {
+  return (10000 <= kind && kind < 20000) || kind == 0 || kind == 3;
+}
+
+/** Events are **ephemeral**, which means they are not expected to be stored by relays. */
+function isEphemeralKind(kind: number) {
+  return 20000 <= kind && kind < 30000;
+}
+
+/** Events are **parameterized replaceable**, which means that, for each combination of `pubkey`, `kind` and the `d` tag, only the latest event is expected to be stored by relays, older versions are expected to be discarded. */
+function isParameterizedReplaceableKind(kind: number) {
+  return 30000 <= kind && kind < 40000;
+}
+
+/** Classification of the event kind. */
+type KindClassification = 'regular' | 'replaceable' | 'ephemeral' | 'parameterized' | 'unknown';
+
+/** Determine the classification of this kind of event if known, or `unknown`. */
+function classifyKind(kind: number): KindClassification {
+  if (isRegularKind(kind)) return 'regular';
+  if (isReplaceableKind(kind)) return 'replaceable';
+  if (isEphemeralKind(kind)) return 'ephemeral';
+  if (isParameterizedReplaceableKind(kind)) return 'parameterized';
+  return 'unknown';
+}
+
+export {
+  classifyKind,
+  isEphemeralKind,
+  isParameterizedReplaceableKind,
+  isRegularKind,
+  isReplaceableKind,
+  type KindClassification,
+};