Typed PubSub subscribe

typedPubsubSubscribe.ts

import { PubSub } from 'graphql-subscriptions';

type PubSubAction = [typeof MESSAGE_ADDED, MessageAddedPayload] | ['foo', 121];

type UnionToIntersection<U> =
  (U extends any ? (k: U) => void : never) extends
    ((k: infer I) => void) ? I : never;

type PairsToRecord<Pair extends [string, any]> =
  Pair extends [infer T1, infer T2]
    ? { [P in Extract<T1, string>]: T2 }
    : never;

type X = PairsToRecord<PubSubAction>;
type Y = UnionToIntersection<X>;

const pubsub = new PubSub() as Assign<
  PubSub,
  {
    publish(...args: PubSubAction): Promise<void>;
    // subscribe(
    //   triggerName: typeof MESSAGE_ADDED,
    //   onMessage: (payload: MessageAddedPayload) => void
    // ): Promise<number>;
    subscribe<TriggerName extends keyof Y>(
      triggerName: TriggerName,
      onMessage: (payload: Y[TriggerName]) => void
    ): Promise<number>
  }
>;