use @snort/system cache

packages/system/src/cache/UserRelayCache.ts

@@ -0,0 +1,29 @@
+import { db, UsersRelays } from ".";
+import { FeedCache } from "@snort/shared";
+
+export class UserRelaysCache extends FeedCache<UsersRelays> {
+  constructor() {
+    super("UserRelays", db.userRelays);
+  }
+
+  key(of: UsersRelays): string {
+    return of.pubkey;
+  }
+
+  override async preload(follows?: Array<string>): Promise<void> {
+    await super.preload();
+    if (follows) {
+      await this.buffer(follows);
+    }
+  }
+
+  newest(): number {
+    let ret = 0;
+    this.cache.forEach(v => (ret = v.created_at > ret ? v.created_at : ret));
+    return ret;
+  }
+
+  takeSnapshot(): Array<UsersRelays> {
+    return [...this.cache.values()];
+  }
+}