rx shareByKey.ts

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  import {defer, finalize, type Observable, share} from 'rxjs';
 
export const shareByKey = <TValue>(sub: (key: string) => Observable<TValue>): ((key: string) => Observable<TValue>) => {
  const map: Record<string, Observable<TValue>> = {};
  return (key: string) => {
    const observable = map[key];
    if (observable) return observable;
    return (map[key] = defer(() => sub(key)).pipe(
      finalize(() => {
        delete map[key];
      }),
      share({
        resetOnRefCountZero: true,
      }),
    ));
  };
};