import { HttpClient } from '@angular/common/http';
import { TranslateLoader } from '@ngx-translate/core';
import { map } from 'rxjs/operators';
import { Observable } from 'rxjs';

interface T {
    [key: string]: string | T;
}

export class PruningTranslationLoader implements TranslateLoader {
    constructor(private _http: HttpClient, private _prefix: string, private _suffix: string) {}

    getTranslation(lang: string): Observable<T> {
        return this._http.get(`${this._prefix}${lang}${this._suffix}`).pipe(map(result => this._process(result as T)));
    }

    private _process(object: T): T {
        return (
            Object.keys(object)
                // eslint-disable-next-line no-prototype-builtins
                .filter(key => object.hasOwnProperty(key) && object[key] !== '')
                .reduce(
                    (result: T, key) => (
                        (result[key] = typeof object[key] === 'object' ? this._process(object[key] as T) : object[key]), result
                    ),
                    {},
                )
        );
    }
}