import { ILayer, ILayers } from './Layer';

export interface IKeyMap extends IterableIterator<ILayer> {
  layers: ILayers;
  [index: number]: ILayer;
}

export class KeyMap implements IKeyMap {
  layers: ILayers = [];
  index: number = 0;

  constructor(layers: ILayers) {
    this.layers = layers;
    this.index = 0;
  }

  [index: number]: ILayer;

  forEach(fn: (k: ILayer, i: number) => any): void {
    return this.layers.forEach(fn);
  }

  map(fn: (k: ILayer, i: number) => ILayer): ILayers {
    return this.layers.map(fn);
  }

  get length(): number {
    return this.layers.length;
  }

  public next(): IteratorResult<ILayer> {
    if (this.index < this.layers.length) {
      return {
        done: false,
        value: this.layers[this.index++],
      };
    }
    return {
      done: true,
      value: null,
    };
  }

  [Symbol.iterator](): IterableIterator<ILayer> {
    return this;
  }
}

export const keymap = (...layers: ILayers): IKeyMap => new KeyMap(layers);
export default keymap;