import type { DomTools } from './domtools.classes.domtools.js';
import * as plugins from './domtools.plugins.js';

export class Scroller {
  public domtoolsInstance: DomTools;
  private disposed = false;

  // Array to store scroll callback functions.
  private scrollCallbacks: Array<() => void> = [];

  // Lenis instance (if activated) or null.
  private lenisInstance: plugins.Lenis | null = null;
  private lenisScrollUnsubscribe: (() => void) | null = null;
  private nativeScrollListenerAttached = false;

  // Bound handlers to allow removal from event listeners.
  private handleNativeScroll = (_event: Event): void => {
    this.executeScrollCallbacks();
  };

  private handleLenisScroll = (_info: plugins.Lenis): void => {
    this.executeScrollCallbacks();
  };

  constructor(domtoolsInstanceArg: DomTools) {
    this.domtoolsInstance = domtoolsInstanceArg;
    // Attach the native scroll listener by default.
    this.attachNativeScrollListener();
  }

  private sweetScroller = new plugins.SweetScroll({});

  /**
   * Scrolls to a given element with options.
   */
  public async toElement(
    elementArg: HTMLElement,
    optionsArg: Parameters<typeof this.sweetScroller.toElement>[1]
  ) {
    this.sweetScroller.toElement(elementArg, optionsArg);
    if (optionsArg?.duration) {
      await plugins.smartdelay.delayFor(optionsArg.duration);
    }
  }

  /**
   * Detects whether native smooth scrolling is enabled.
   */
  public async detectNativeSmoothScroll() {
    const rootScrollBehavior = getComputedStyle(document.documentElement).scrollBehavior;
    const bodyScrollBehavior = document.body ? getComputedStyle(document.body).scrollBehavior : 'auto';
    if (rootScrollBehavior === 'smooth' || bodyScrollBehavior === 'smooth') {
      return true;
    }

    const done = plugins.smartpromise.defer<boolean>();
    const sampleSize = 12;
    const acceptableDeltaDifference = 3;
    const minimumSmoothRatio = 0.75;
    const timeoutInMs = 1200;

    const eventDeltas: number[] = [];

    const finalize = (result: boolean) => {
      window.removeEventListener('wheel', onWheel);
      window.clearTimeout(timeoutId);
      done.resolve(result);
    };

    function onWheel(event: WheelEvent) {
      eventDeltas.push(event.deltaY);

      if (eventDeltas.length >= sampleSize) {
        analyzeEvents();
      }
    }

    function analyzeEvents() {
      if (eventDeltas.length < 2) {
        finalize(false);
        return;
      }

      const totalDiffs = eventDeltas.length - 1;
      let smallDiffCount = 0;

      for (let i = 0; i < totalDiffs; i++) {
        const diff = Math.abs(eventDeltas[i + 1] - eventDeltas[i]);
        if (diff <= acceptableDeltaDifference) {
          smallDiffCount++;
        }
      }

      const smoothRatio = smallDiffCount / totalDiffs;
      finalize(smoothRatio >= minimumSmoothRatio);
    }

    const timeoutId = window.setTimeout(() => {
      analyzeEvents();
    }, timeoutInMs);

    window.addEventListener('wheel', onWheel, { passive: true });
    return done.promise;
  }

  /**
   * Enables Lenis scrolling.
   * If optionsArg.disableOnNativeSmoothScroll is true and native smooth scrolling is detected,
   * Lenis will be destroyed immediately.
   */
  public async enableLenisScroll(optionsArg?: { disableOnNativeSmoothScroll?: boolean }) {
    if (this.disposed) {
      return;
    }

    if (this.lenisInstance) {
      this.disableLenisScroll();
    }

    const lenis = new plugins.Lenis({
      autoRaf: true,
    });

    if (optionsArg?.disableOnNativeSmoothScroll) {
      if (await this.detectNativeSmoothScroll()) {
        lenis.destroy();
        return;
      }
    }

    // Activate Lenis scrolling.
    this.lenisInstance = lenis;
    // Switch from native scroll listener to Lenis scroll listener.
    this.detachNativeScrollListener();
    this.attachLenisScrollListener();
  }

  public disableLenisScroll() {
    if (!this.lenisInstance) {
      return;
    }

    this.detachLenisScrollListener();
    this.lenisInstance.destroy();
    this.lenisInstance = null;
    this.attachNativeScrollListener();
  }

  /**
   * Registers a callback to be executed on scroll.
   * @param callback A function to execute on each scroll event.
   */
  public onScroll(callback: () => void): () => void {
    this.scrollCallbacks.push(callback);
    return () => {
      this.scrollCallbacks = this.scrollCallbacks.filter((existingCallback) => existingCallback !== callback);
    };
  }

  /**
   * Executes all registered scroll callbacks concurrently.
   */
  private executeScrollCallbacks(): void {
    // Execute all callbacks in parallel.
    this.scrollCallbacks.forEach((callback) => {
      try {
        callback();
      } catch (error) {
        console.error('Error in scroll callback:', error);
      }
    });
  }

  /**
   * Attaches the native scroll event listener.
   */
  private attachNativeScrollListener(): void {
    if (this.nativeScrollListenerAttached || this.disposed) {
      return;
    }
    window.addEventListener('scroll', this.handleNativeScroll);
    this.nativeScrollListenerAttached = true;
  }

  /**
   * Detaches the native scroll event listener.
   */
  private detachNativeScrollListener(): void {
    if (!this.nativeScrollListenerAttached) {
      return;
    }
    window.removeEventListener('scroll', this.handleNativeScroll);
    this.nativeScrollListenerAttached = false;
  }

  /**
   * Attaches the Lenis scroll event listener.
   */
  private attachLenisScrollListener(): void {
    if (this.lenisInstance && !this.lenisScrollUnsubscribe) {
      this.lenisScrollUnsubscribe = this.lenisInstance.on('scroll', this.handleLenisScroll);
    }
  }

  /**
   * Detaches the Lenis scroll event listener.
   */
  private detachLenisScrollListener(): void {
    if (this.lenisScrollUnsubscribe) {
      this.lenisScrollUnsubscribe();
      this.lenisScrollUnsubscribe = null;
    }
  }

  public dispose() {
    if (this.disposed) {
      return;
    }

    this.disposed = true;
    this.detachLenisScrollListener();
    this.lenisInstance?.destroy();
    this.lenisInstance = null;
    this.detachNativeScrollListener();
    this.scrollCallbacks = [];
    this.sweetScroller.destroy();
  }
}