import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'sortBy'
})
export class SortByPipe implements PipeTransform {

  /**
   * Sort an array by multiple elements.
   *
   * Example to sort an array respectively by Year, Album, Disc Number, etc.
   * Typescript usage:
   * <pre>
   * new SortByPipe().transform(this.songs, 'Year', 'Album', 'Disc Number', 'Track Number', 'Play Count');
   * </pre>
   * In HTML usage:
   * <pre>
   * <tr *ngFor="let song of songs | sortBy : 'Year':'Album':'Disc Number':'Track Number'">
   * </pre>
   *
   * @param array array to sort
   * @param args elements used to sort in oder
   */
  transform(array: Array<any>, ...args: any[]): Array<any> {
    array.sort((a: any, b: any) => {
      for (let i = 0; i < args.length; i++) {
        const arg = args[i];

        if (a[arg] === undefined && b[arg] !== undefined) { return -1; }
        if (a[arg] !== undefined && b[arg] === undefined) { return 1; }

        if (a[arg] < b[arg]) { return -1; }
        if (a[arg] > b[arg]) { return 1; }
      }
      return 0;
    });
    return array;
  }

}