import { Injectable } from '@angular/core';
import { Observable, Subject } from 'rxjs';

/**
 * The data provider service class
 *
 * @export
 * @class DataProviderService
 */
@Injectable()
export class DataProviderService {
  /**
   * Subscriber to request data action
   *
   * @private
   * @type {Subject<any>}
   * @memberof DataProviderService
   */
  private requestData: Subject<any> = new Subject<any>();

  /**
   * Max page size;
   *
   * @memberof DataProviderService
   */
  maxPageSize = 10;

  /**
   * Subscriber to know comboboxItemCount.
   *
   * @private
   * @type {Subject<any>}
   * @memberof DataProviderService
   */
  private itemsCount: Subject<any> = new Subject<any>();

  /**
   * DataSource array
   *
   * @type {any[]}
   * @memberof DataProviderService
   */
  dataSource: any[];

  /**
   * Function that generates the collection that will be assigned
   * to the virtual scrolled component
   *
   * @memberof DataProviderService
   */
  pageResolver: (items: any[], skip: number, take: number) => any;

  /**
   * API to retrieve the data from the component provider
   *
   * @param {number} skip
   * @param {number} take
   * @return {*}
   * @memberof DataProviderService
   */
  getPage(skip: number, take: number): void {
    this.pageResolver(this.dataSource, skip, take);
  }

  /**
   * Emit the selection action to trigger the
   * load event every time the component is selected
   *
   * @param {number} index
   * @memberof DataProviderService
   */
  emitRequestDataAction(index: number): void {
    this.requestData.next(index);
  }

  /**
   * Emits the current status of items counting.
   *
   * @param {*} data
   * @memberof DataProviderService
   */
  emitItemsCountDataAction(data: any): void {
    this.itemsCount.next(data);
  }

  /**
   * Subscribe to this to trigger the load event when
   * the tab is selected.
   *
   * @readonly
   * @type {Observable<any>}
   * @memberof TabItemService
   */
  get requestDataEvent(): Observable<any> {
    return this.requestData.asObservable();
  }

  /**
   * Gets the current status of items counting
   *
   * @readonly
   * @type {Observable<any>}
   * @memberof DataProviderService
   */
  get itemsCountChanging(): Observable<any> {
    return this.itemsCount.asObservable();
  }
}