import { Iterable } from 'ix';

import { IterableLike, ObservableLike, ReadOnlyProperty } from '../../../WebRx';
import { BaseViewModel } from '../../React';

export class ItemsViewModel<T> extends BaseViewModel {
  public static displayName = 'ItemsViewModel';

  protected readonly emptySource = Iterable.empty<T>();

  public readonly source: ReadOnlyProperty<IterableLike<T>>;
  public readonly count: ReadOnlyProperty<number>;

  constructor(source: ObservableLike<IterableLike<T>>) {
    super();

    this.source = this.wx
      .getObservableOrAlert(() => {
        return this.wx.getObservable(source).map(x => Iterable.from(x));
      }, 'Invalid Items Source')
      .toProperty(this.emptySource, false);

    this.count = this.wx
      .whenAny(this.source, x => Iterable.from(x || []).count())
      .toProperty();
  }

  public getItemsSourceProperty(): ReadOnlyProperty<IterableLike<T>> {
    return this.source;
  }

  public getItemsSource() {
    return this.getItemsSourceProperty().value;
  }

  public getItems() {
    return Iterable.from(this.getItemsSource());
  }

  public getItemAt(index: number) {
    return this.getItems().elementAt(index);
  }
}