import { TRequiredProps } from '@/internal/requiredProps';
import { clamp } from '@/utils/math';
import {
  IInViewCallbacksMap,
  IInViewElement,
  IInViewMutableProps,
  IInViewStaticProps,
} from './types';
import { Module } from '@/base/Module';
import { initVevet } from '@/global/initVevet';

export * from './types';

/**
 * InView is a visibility detection utility that leverages the `IntersectionObserver` API to monitor when elements enter or leave the viewport.
 * It provides customizable options for triggering events, delaying visibility changes, and dynamically adding CSS classes to elements based on their visibility state.
 *
 * [Documentation](https://antonbobrov.github.io/vevet/docs/components/InView)
 *
 * @group Components
 */
export class InView<
  CallbacksMap extends IInViewCallbacksMap = IInViewCallbacksMap,
  StaticProps extends IInViewStaticProps = IInViewStaticProps,
  MutableProps extends IInViewMutableProps = IInViewMutableProps,
> extends Module<CallbacksMap, StaticProps, MutableProps> {
  /**
   * Returns default static properties.
   */
  public _getStatic(): TRequiredProps<StaticProps> {
    return {
      ...super._getStatic(),
      hasOut: true,
      maxInitialDelay: 1000,
      scrollDirection: 'vertical',
    } as TRequiredProps<StaticProps>;
  }

  /**
   * Returns default mutable properties.
   */
  public _getMutable(): TRequiredProps<MutableProps> {
    return {
      ...super._getMutable(),
      enabled: true,
      rootMargin: '0% 0% -5% 0%',
    } as TRequiredProps<MutableProps>;
  }

  /** Intersection observer for detecting elements entering the viewport. */
  protected _observerIn?: IntersectionObserver;

  /** Intersection observer for detecting elements leaving the viewport. */
  protected _observerOut?: IntersectionObserver;

  /** Tracks whether this is the first time the elements are being observed. */
  protected _isInitialStart = true;

  /**
   * Indicates whether the observation has started for the first time.
   */
  get isInitialStart() {
    return this._isInitialStart;
  }

  /** Stores the elements being observed. */
  protected _elements: IInViewElement[] = [];

  /**
   * Returns all elements currently being observed.
   */
  get elements() {
    return this._elements;
  }

  /**
   * Initializes the `InView` module.
   */
  constructor(props?: StaticProps & MutableProps) {
    super(props);

    this._setup();
  }

  /**
   * Handles property mutations and updates observation events accordingly.
   */
  protected _handleProps() {
    super._handleProps();

    this._setup();
  }

  /**
   * Configures or reconfigures the view observation events.
   */
  protected _setup() {
    this._removeViewEvents();

    if (this.props.enabled) {
      this._setViewEvents();
    }
  }

  /**
   * Removes all observation events and disconnects observers.
   */
  protected _removeViewEvents() {
    this._observerIn?.disconnect();
    this._observerIn = undefined;

    this._observerOut?.disconnect();
    this._observerOut = undefined;
  }

  /**
   * Sets up `IntersectionObserver` instances to detect visibility changes.
   */
  protected _setViewEvents() {
    const { isInitialStart, props } = this;
    const rootMargin = isInitialStart ? '0% 0% 0% 0%' : props.rootMargin;

    this._observerIn = new IntersectionObserver(
      (data) => this._handleIn(data),
      { root: null, threshold: 0, rootMargin },
    );

    this.elements.forEach((element) => this._observerIn?.observe(element));

    if (props.hasOut) {
      this._observerOut = new IntersectionObserver(
        (data) => this._handleOut(data),
        { root: null, threshold: 0, rootMargin: '0px 0px 0px 0px' },
      );

      this.elements.forEach((element) => this._observerOut?.observe(element));
    }
  }

  /**
   * Handles elements entering the viewport.
   */
  protected _handleIn(data: IntersectionObserverEntry[]) {
    data.forEach((entry) => {
      const element = entry.target as IInViewElement;

      if (!entry.isIntersecting || element.$vevetInViewBool) {
        return;
      }

      element.$vevetInViewBool = true;

      if (element.$vevetInViewTimeout) {
        clearTimeout(element.$vevetInViewTimeout);
      }

      element.$vevetInViewTimeout = setTimeout(
        () => this._handleInOut(element, true),
        this._getElementDelay(element),
      );

      if (!this.props.hasOut) {
        this.removeElement(element);
      }
    });

    if (this._isInitialStart) {
      this._isInitialStart = false;

      this._setup();
    }
  }

  /**
   * Handles elements leaving the viewport.
   */
  protected _handleOut(data: IntersectionObserverEntry[]) {
    data.forEach((entry) => {
      const element = entry.target as IInViewElement;

      if (entry.isIntersecting || !element.$vevetInViewBool) {
        return;
      }

      element.$vevetInViewBool = false;

      if (element.$vevetInViewTimeout) {
        clearTimeout(element.$vevetInViewTimeout);
      }

      element.$vevetInViewTimeout = setTimeout(() => {
        this._handleInOut(element, false);
      }, 0);
    });
  }

  /**
   * Toggles visibility classes and emits events for visibility changes.
   */
  protected _handleInOut(element: IInViewElement, isInView: boolean) {
    const className = element.getAttribute('data-in-view-class');

    if (className) {
      element.classList.toggle(className, isInView);
    }

    this.callbacks.emit(isInView ? 'in' : 'out', { element });
  }

  /**
   * Calculates the delay before triggering an element's visibility event.
   */
  protected _getElementDelay(element: IInViewElement) {
    const { props } = this;
    const app = initVevet();

    if (!this.isInitialStart || props.maxInitialDelay <= 0) {
      return 0;
    }

    const bounding = element.getBoundingClientRect();

    const rootBounding = {
      top: 0,
      left: 0,
      width: app.width,
      height: app.height,
    };

    const progress = clamp(
      props.scrollDirection === 'horizontal'
        ? (bounding.left - rootBounding.left) / rootBounding.width
        : (bounding.top - rootBounding.top) / rootBounding.height,
      0,
      1,
    );

    return progress * props.maxInitialDelay;
  }

  /**
   * Registers an element for visibility observation.
   *
   * If the element has a `data-in-view-class` attribute, the specified class will be applied upon entering the viewport.
   *
   * @returns A function to stop observing the element.
   */
  public addElement(element: Element) {
    const finalElement = element as IInViewElement;
    finalElement.$vevetInViewBool = undefined;

    this._elements.push(finalElement);

    this._observerIn?.observe(finalElement);
    this._observerOut?.observe(finalElement);

    return () => this.removeElement(finalElement);
  }

  /**
   * Removes an element from observation, preventing further visibility tracking.
   */
  public removeElement(element: Element) {
    const finalElement = element as IInViewElement;

    this._observerIn?.unobserve(finalElement);
    this._observerOut?.unobserve(finalElement);

    this._elements = this._elements.filter((el) => el !== element);

    finalElement.$vevetInViewBool = undefined;
  }

  /**
   * Cleans up the module and disconnects all observers and listeners.
   */
  protected _destroy() {
    super._destroy();

    this._removeViewEvents();
  }
}