import { combineLatest, Observable, of } from 'rxjs';
import { map, startWith } from 'rxjs/operators';
import { ValuesOf } from './types/utility-types';

export class ContextComponent<T> {
    componentContext$: Observable<T> | null = of({} as T);

    protected _initContext(context: Record<string, Observable<ValuesOf<T>>>): void {
        const observables = Object.values(context).map(obs => obs.pipe(startWith(null)));
        const keys = Object.keys(context);
        this.componentContext$ = combineLatest(observables).pipe(map(values => this._mapKeysToObs(keys, values)));
    }

    protected _mapKeysToObs(keys: string[], observables: (ValuesOf<T> | null)[]): T {
        return keys.reduce((acc, key, index) => ({ ...acc, [key]: observables[index] }), {} as T);
    }
}