add utilities to convert nostr npubs to and from hex strings

src/nostr.ts

@@ -1,6 +1,7 @@
 import NDK, {NDKEvent, NDKPrivateKeySigner, NDKUser} from "@nostr-dev-kit/ndk";
 import {generateSecretKey} from "nostr-tools";
 import {randomTimeUpTo2DaysInThePast} from "./general.ts";
+import {decode as nip19Decode, npubEncode} from "nostr-tools/nip19";
 
 export async function encryptEventForRecipient(
   ndk: NDK,
@@ -25,3 +26,14 @@ export async function encryptEventForRecipient(
   giftWrap.ndk = ndk;
   return giftWrap;
 }
+
+export function npubToPubKeyString(npub: string) {
+  const decoded = nip19Decode(npub);
+  if (decoded.type !== 'npub')
+    throw new Error('Invalid npub');
+  return decoded.data;
+}
+
+export function pubKeyStringToNpub(pubKey: string) {
+  return npubEncode(pubKey);
+}