import { IKeyRow, IKeyRows } from './Row';

export interface ILayer extends IterableIterator<IKeyRow> {
  rows: IKeyRows;
  index: number;
  length: number;
  forEach(fn: (k: IKeyRow, i: number) => any): void;
  map(fn: (k: IKeyRow, i: number) => IKeyRow): IKeyRows;
}

export type ILayers = ILayer[];

class Layer implements ILayer {
  rows: IKeyRows = [];
  index: number = 0;

  constructor(rows: IKeyRows) {
    this.rows = rows;
    this.index = 0;
  }

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

  map(fn: (k: IKeyRow, i: number) => IKeyRow): IKeyRows {
    return this.rows.map(fn);
  }

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

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

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

export const layer = (...rows: IKeyRows): ILayer => new Layer(rows);
export default layer;