heppokofrontend/pager

/** Wrapping iterable objects with the pager function */
export class Pager<T = any> {
  #_index = 0;
  public values: T[];

  /**
   * Switch the current page
   * @param index - Page number to move to
   * @returns - Items on the current page.
   */
  public current(index: number) {
    this.index = index;

    return this.page;
  }

  /**
   * Switch the current page to the next.
   * @returns - Items on the next page.
   */
  public next() {
    return this.current(++this.index);
  }

  /**
   * Switch the current page to the previous.
   * @returns - Items on the previous page.
   */
  public prev() {
    return this.current(--this.index);
  }

  /** @returns - Last page number */
  get lastIndex() {
    return Math.ceil(this.values.length / this.views);
  }

  /** @param index - Page number to move to */
  set index(index) {
    if (index < 0) {
      this.#_index = 0;

      return;
    }

    if (this.lastIndex <= index) {
      this.index = this.lastIndex - 1;

      return;
    }

    this.#_index = index;
  }

  /** @returns - The current page number */
  get index() {
    return this.#_index;
  }

  /** @returns - Items on the current page */
  get page() {
    const {views, index} = this;
    const start = index * views;

    return this.values.slice(start, start + views);
  }

  /** A generator that returns this.values */
  * [Symbol.iterator]() {
    yield* this.values;
  }

  /**
   * @param values - Iterable objects to be managed by the pager
   * @param views - Number of items to be displayed per page
   */
  constructor(values: Iterable<T>, public views = 5) {
    if (typeof values[Symbol.iterator] !== 'function') {
      throw new TypeError('The first argument must be an iterable.');
    }

    this.values = [...values];

    Object.defineProperty(this, 'values', {
      value: this.values,
    });
  }
}