sattle/src/lnurlcash/nostr/transport.ts

// The relay-facing transport for nostr backup, kept injectable so tests
// never touch a network. The default is nostr-tools' SimplePool, imported
// lazily: merely importing the backup module must never open (or even
// reference) a WebSocket.

import type { Filter as NostrFilter } from 'nostr-tools/filter';

import type { NostrEvent } from './events';

export type { NostrFilter };

// publish throws when the event was accepted NOWHERE
export type BackupTransport = {
  publish: (relays: string[], event: NostrEvent) => Promise<void>;
  fetch: (relays: string[], filter: NostrFilter) => Promise<NostrEvent[]>;
};

export const defaultTransport = async (): Promise<BackupTransport> => {
  const { SimplePool } = await import('nostr-tools/pool');
  const pool = new SimplePool();
  return {
    publish: async (relays, event) => {
      const results = await Promise.allSettled(pool.publish(relays, event));
      // one honest relay keeping the event is enough - addressable events
      // are re-publishable, and the next debounced publish retries anyway
      if (!results.some((r) => r.status === 'fulfilled')) {
        throw new Error('No relay accepted the backup event.');
      }
    },
    fetch: (relays, filter) => pool.querySync(relays, filter),
  };
};