import { join } from 'path';
import { forkJoin, Observable, of, UnaryFunction } from 'rxjs';
import { catchError, map, mapTo, mergeMap } from 'rxjs/operators';

import { rxStats } from './rx.walk';

/**
 * Locates the first directory that contains a certain file
 *
 * @param aSources  the list of source files to check
 * @param aRelPath  the relative path
 *
 * @return the observable
 */
export function rxFindDir(aSources: Observable<string[]>, aRelPath: string, aMkdirp: UnaryFunction<string, Observable<string>>): Observable<string> {
    // map each source to a check
    return aSources.pipe(
        mergeMap(sources => forkJoin(
            sources.map(dir => rxStats(join(dir, aRelPath)).pipe(mapTo(dir), catchError(err => of(null))))
        ).pipe(
            map(result => result.filter(Boolean)),
            map(result => (result.length > 0) ? result[0]! : sources[0]!)
        )),
        mergeMap(aMkdirp)
    );
}