Add proper p tags for replies and mentions

src/lib/mentions.ts

@@ -0,0 +1,46 @@
+import * as nip19 from "@nostr/tools/nip19";
+import { loadRelayList } from "@nostr/gadgets/lists";
+
+const RELAY_HINT_TIMEOUT_MS = 1500;
+
+export function extractMentionPubkeys(content: string): string[] {
+  const re = /nostr:(npub1[a-z0-9]+|nprofile1[a-z0-9]+)/gi;
+  const out = new Set<string>();
+  for (const m of content.matchAll(re)) {
+    try {
+      const decoded = nip19.decode(m[1]);
+      if (decoded.type === "npub") out.add(decoded.data);
+      else if (decoded.type === "nprofile") out.add(decoded.data.pubkey);
+    } catch {
+      // Invalid bech32, skip
+    }
+  }
+  return [...out];
+}
+
+export async function relayHintFor(pubkey: string): Promise<string | undefined> {
+  try {
+    const TIMEOUT = Symbol();
+    const result = await Promise.race([
+      loadRelayList(pubkey),
+      new Promise<typeof TIMEOUT>((resolve) =>
+        setTimeout(() => resolve(TIMEOUT), RELAY_HINT_TIMEOUT_MS),
+      ),
+    ]);
+    if (result === TIMEOUT) return undefined;
+    return result.items.find((r) => r.write)?.url;
+  } catch {
+    return undefined;
+  }
+}
+
+export async function buildPTagHints(pubkeys: Iterable<string>): Promise<Map<string, string>> {
+  const hints = new Map<string, string>();
+  await Promise.all(
+    [...pubkeys].map(async (pk) => {
+      const url = await relayHintFor(pk);
+      if (url) hints.set(pk, url);
+    }),
+  );
+  return hints;
+}