sattle/src/lnurlcash/nwc/transport.ts

// The relay-facing transport for the NWC service, kept injectable so
// tests never touch a network. Same pattern as nostr/transport.ts: the
// default (nostr-tools' SimplePool) is imported lazily, so merely
// importing the service module never opens (or even references) a
// WebSocket.

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

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

export type { NostrFilter };

export type NwcSubscription = {
  close: () => void;
};

export type NwcTransport = {
  publish: (relays: string[], event: NostrEvent) => Promise<void>;
  subscribe: (
    relays: string[],
    filter: NostrFilter,
    onEvent: (event: NostrEvent) => void,
  ) => NwcSubscription;
};

export const defaultNwcTransport = async (): Promise<NwcTransport> => {
  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 accepting is enough - same rule as the backup
      if (!results.some((r) => r.status === 'fulfilled')) {
        throw new Error('No relay accepted the event.');
      }
    },
    subscribe: (relays, filter, onEvent) =>
      pool.subscribeMany(relays, filter, { onevent: onEvent }),
  };
};