import { ARROW_LEFT, ARROW_RIGHT } from '../../constants/arrows';
import {
  ARIA_CONTROLS,
  ARIA_LABEL,
  ARIA_ORIENTATION,
  ARIA_SELECTED,
  ROLE,
  TAB_INDEX,
} from '../../constants/attributes';
import { CLASS_ACTIVE, CLASS_PAGINATION } from '../../constants/classes';
import { TTB } from '../../constants/directions';
import {
  EVENT_END_INDEX_CHANGED,
  EVENT_MOVE,
  EVENT_PAGINATION_MOUNTED,
  EVENT_PAGINATION_UPDATED,
  EVENT_REFRESH,
  EVENT_SCROLL,
  EVENT_SCROLLED,
  EVENT_UPDATED,
} from '../../constants/events';
import { BaseComponent, ComponentConstructor, Options } from '../../types';
import {
  addClass,
  apply,
  ceil,
  create,
  display,
  empty,
  focus,
  format,
  prevent,
  removeAttribute,
  removeClass,
  removeNode,
  setAttribute,
  slice,
} from '@splidejs/utils';


/**
 * The interface for the Pagination component.
 *
 * @since 3.0.0
 */
export interface PaginationComponent extends BaseComponent {
  readonly items: PaginationItem[];
  getAt(index: number): PaginationItem;
  update(): void;
}

/**
 * The interface for data of the pagination.
 *
 * @since 3.0.0
 */
export interface PaginationData {
  readonly list: HTMLUListElement;
  readonly items: PaginationItem[];
}

/**
 * The interface for each pagination item.
 *
 * @since 3.0.0
 */
export interface PaginationItem {
  readonly li: HTMLLIElement;
  readonly button: HTMLButtonElement;
  readonly page: number;
}

/**
 * The component for the pagination UI (a slide picker).
 *
 * @since 3.0.0
 *
 * @param Splide     - A Splide instance.
 * @param Components - A collection of components.
 * @param options    - Options.
 * @param event      - An EventInterface instance.
 *
 * @return A Pagination component object.
 */
export const Pagination: ComponentConstructor<PaginationComponent> = (Splide, Components, options, event) => {
  const { on, emit, bind } = event;
  const { Slides, Elements, Controller } = Components;
  const { hasFocus, getIndex, go } = Controller;
  const { resolve } = Components.Direction;
  const { pagination: placeholder } = Elements;

  /**
   * Stores all pagination items.
   */
  const items: PaginationItem[] = [];

  /**
   * The pagination element.
   */
  let list: HTMLUListElement | null;

  /**
   * Holds modifier classes.
   */
  let paginationClasses: string;

  /**
   * Called when the component is mounted.
   */
  function mount(): void {
    destroy();
    on([EVENT_UPDATED, EVENT_REFRESH, EVENT_END_INDEX_CHANGED], mount);

    const { pagination: enabled = true } = options;
    placeholder && display(placeholder, enabled ? '' : 'none');

    if (enabled) {
      on([EVENT_MOVE, EVENT_SCROLL, EVENT_SCROLLED], update);
      createPagination();
      update();
      emit(EVENT_PAGINATION_MOUNTED, { list, items }, getAt(Splide.index));
    }
  }

  /**
   * Destroys the component.
   */
  function destroy(): void {
    if (list) {
      removeNode(placeholder ? slice(list.children) : list);
      removeClass(list, paginationClasses);
      empty(items);
      list = null;
    }

    event.destroy();
  }

  /**
   * Creates the pagination element and appends it to the slider.
   */
  function createPagination(): void {
    const { length } = Splide;
    const { classes, i18n, perPage, paginationKeyboard = true } = options;
    const max = hasFocus() ? Controller.getEnd() + 1 : ceil(length / perPage);
    const dir = getDirection();

    list = placeholder || create('ul', classes.pagination, Elements.track.parentElement);

    addClass(list, (paginationClasses = `${ CLASS_PAGINATION }--${ dir }`));
    setAttribute(list, ROLE, 'tablist');
    setAttribute(list, ARIA_LABEL, i18n.select);
    setAttribute(list, ARIA_ORIENTATION, dir === TTB ? 'vertical' : '');

    for (let i = 0; i < max; i++) {
      const li = create('li', null, list);
      const button = create('button', { class: classes.page, type: 'button' }, li);
      const controls = Slides.getIn(i).map(Slide => Slide.slide.id);
      const text = !hasFocus() && perPage > 1 ? i18n.pageX : i18n.slideX;

      bind(button, 'click', () => go(`>${ i }`));
      paginationKeyboard && bind(button, 'keydown', apply(onKeydown, i));

      setAttribute(li, ROLE, 'presentation');
      setAttribute(button, ROLE, 'tab');
      setAttribute(button, ARIA_CONTROLS, controls.join(' '));
      setAttribute(button, ARIA_LABEL, format(text, i + 1));
      setAttribute(button, TAB_INDEX, -1);

      items.push({ li, button, page: i });
    }
  }

  /**
   * Called when any key is pressed on the pagination.
   *
   * @link https://www.w3.org/WAI/ARIA/apg/patterns/tabpanel/#keyboard-interaction-21
   *
   * @param page - A page index.
   * @param e    - A KeyboardEvent object.
   */
  function onKeydown(page: number, e: KeyboardEvent): void {
    const { length } = items;
    const { key } = e;
    const dir = getDirection();

    let nextPage = -1;

    if (key === resolve(ARROW_RIGHT, false, dir)) {
      nextPage = ++page % length;
    } else if (key === resolve(ARROW_LEFT, false, dir)) {
      nextPage = (--page + length) % length;
    } else if (key === 'Home') {
      nextPage = 0;
    } else if (key === 'End') {
      nextPage = length - 1;
    }

    const item = items[nextPage];

    if (item) {
      focus(item.button);
      go(`>${ nextPage }`);
      prevent(e, true);
    }
  }

  /**
   * Returns the latest direction for pagination.
   *
   * @return The direction for pagination.
   */
  function getDirection(): Options[ 'direction' ] {
    return options.paginationDirection || options.direction;
  }

  /**
   * Returns the pagination item at the specified index.
   *
   * @param index - An index.
   *
   * @return A pagination item object if available, or otherwise `undefined`.
   */
  function getAt(index: number): PaginationItem | undefined {
    return items[Controller.toPage(index)];
  }

  /**
   * Updates the pagination status.
   */
  function update(): void {
    const prev = getAt(getIndex(true));
    const curr = getAt(getIndex());

    if (prev) {
      const { button } = prev;
      removeClass(button, CLASS_ACTIVE);
      removeAttribute(button, ARIA_SELECTED);
      setAttribute(button, TAB_INDEX, -1);
    }

    if (curr) {
      const { button } = curr;
      addClass(button, CLASS_ACTIVE);
      setAttribute(button, ARIA_SELECTED, true);
      setAttribute(button, TAB_INDEX, '');
    }

    emit(EVENT_PAGINATION_UPDATED, { list, items }, prev, curr);
  }

  return {
    items,
    mount,
    destroy,
    getAt,
    update,
  };
};