import type { ComponentInterface, EventEmitter } from '@stencil/core';
import { Component, Element, Event, Host, Method, Prop, State, Watch, h, readTask, writeTask } from '@stencil/core';
import { getTimeGivenProgression } from '@utils/animation/cubic-bezier';
import {
  getScrollElement,
  ION_CONTENT_CLASS_SELECTOR,
  ION_CONTENT_ELEMENT_SELECTOR,
  printIonContentErrorMsg,
} from '@utils/content';
import { clamp, componentOnReady, getElementRoot, raf, transitionEndAsync } from '@utils/helpers';
import { printIonError } from '@utils/logging';
import { ImpactStyle, hapticImpact } from '@utils/native/haptic';

import { getIonMode, getIonTheme } from '../../global/ionic-global';
import type { Animation, Gesture, GestureDetail } from '../../interface';

import type { RefresherEventDetail, RefresherPullEndEventDetail } from './refresher-interface';
import {
  createPullingAnimation,
  createSnapBackAnimation,
  getRefresherAnimationType,
  handleScrollWhilePulling,
  handleScrollWhileRefreshing,
  setSpinnerOpacity,
  shouldUseNativeRefresher,
  translateElement,
} from './refresher.utils';

/**
 * @virtualProp {"ios" | "md"} mode - The mode determines the platform behaviors of the component.
 * @virtualProp {"ios" | "md" | "ionic"} theme - The theme determines the visual appearance of the component.
 */
@Component({
  tag: 'ion-refresher',
  styleUrls: {
    ios: 'refresher.ios.scss',
    md: 'refresher.md.scss',
    ionic: 'refresher.md.scss',
  },
})
export class Refresher implements ComponentInterface {
  private appliedStyles = false;
  private didStart = false;
  private progress = 0;
  private scrollEl?: HTMLElement;
  private backgroundContentEl?: HTMLElement;
  private scrollListenerCallback?: () => void;
  private gesture?: Gesture;
  private overflowStyles?: { [key: string]: string };

  private pointerDown = false;
  private needsCompletion = false;
  private didRefresh = false;
  private contentFullscreen = false;
  private lastVelocityY = 0;
  private elementToTransform?: HTMLElement;
  private animations: Animation[] = [];

  @State() private nativeRefresher = false;

  @Element() el!: HTMLIonRefresherElement;

  /**
   * The current state which the refresher is in. The refresher's states include:
   *
   * - `inactive` - The refresher is not being pulled down or refreshing and is currently hidden.
   * - `pulling` - The user is actively pulling down the refresher, but has not reached the point yet that if the user lets go, it'll refresh.
   * - `cancelling` - The user pulled down the refresher and let go, but did not pull down far enough to kick off the `refreshing` state. After letting go, the refresher is in the `cancelling` state while it is closing, and will go back to the `inactive` state once closed.
   * - `ready` - The user has pulled down the refresher far enough that if they let go, it'll begin the `refreshing` state.
   * - `refreshing` - The refresher is actively waiting on the async operation to end. Once the refresh handler calls `complete()` it will begin the `completing` state.
   * - `completing` - The `refreshing` state has finished and the refresher is in the way of closing itself. Once closed, the refresher will go back to the `inactive` state.
   */
  @State() private state: RefresherState = RefresherState.Inactive;

  /**
   * The minimum distance the user must pull down until the
   * refresher will go into the `refreshing` state.
   * Does not apply when the refresher content uses a spinner,
   * enabling the native refresher.
   */
  @Prop() pullMin = 60;

  /**
   * The maximum distance of the pull until the refresher
   * will automatically go into the `refreshing` state.
   * Defaults to the result of `pullMin + 60`.
   * Does not apply when  the refresher content uses a spinner,
   * enabling the native refresher.
   */
  @Prop() pullMax: number = this.pullMin + 60;

  /**
   * Time it takes to close the refresher.
   * Does not apply when the refresher content uses a spinner,
   * enabling the native refresher.
   */
  @Prop() closeDuration = '280ms';

  /**
   * Time it takes the refresher to snap back to the `refreshing` state.
   * Does not apply when the refresher content uses a spinner,
   * enabling the native refresher.
   */
  @Prop() snapbackDuration = '280ms';

  /**
   * How much to multiply the pull speed by. To slow the pull animation down,
   * pass a number less than `1`. To speed up the pull, pass a number greater
   * than `1`. The default value is `1` which is equal to the speed of the cursor.
   * If a negative value is passed in, the factor will be `1` instead.
   *
   * For example, If the value passed is `1.2` and the content is dragged by
   * `10` pixels, instead of `10` pixels, the content will be pulled by `12` pixels
   * (an increase of 20 percent). If the value passed is `0.8`, the dragged amount
   * will be `8` pixels, less than the amount the cursor has moved.
   *
   * Does not apply when the refresher content uses a spinner,
   * enabling the native refresher.
   */
  @Prop() pullFactor = 1;

  /**
   * If `true`, the refresher will be hidden.
   */
  @Prop() disabled = false;
  @Watch('disabled')
  disabledChanged() {
    if (this.gesture) {
      this.gesture.enable(!this.disabled);
    }
  }

  /**
   * Emitted when the user lets go of the content and has pulled down
   * further than the `pullMin` or pulls the content down and exceeds the pullMax.
   * Updates the refresher state to `refreshing`. The `complete()` method should be
   * called when the async operation has completed.
   */
  @Event() ionRefresh!: EventEmitter<RefresherEventDetail>;

  /**
   * Emitted while the user is pulling down the content and exposing the refresher.
   */
  @Event() ionPull!: EventEmitter<void>;

  // TODO(FW-7044): Remove this in a major release
  /**
   * Emitted when the user begins to start pulling down.
   *
   * @deprecated Use `ionPullStart` instead.
   */
  @Event() ionStart!: EventEmitter<void>;

  /**
   * Emitted when the user begins to start pulling down.
   */
  @Event() ionPullStart!: EventEmitter<void>;

  /**
   * Emitted when the refresher has returned to the inactive state
   * after a pull gesture. This fires whether the refresh completed
   * successfully or was canceled.
   */
  @Event() ionPullEnd!: EventEmitter<RefresherPullEndEventDetail>;

  private async checkNativeRefresher() {
    const useNativeRefresher = await shouldUseNativeRefresher(this.el, getIonMode(this));
    if (useNativeRefresher && !this.nativeRefresher) {
      const contentEl = this.el.closest('ion-content');
      this.setupNativeRefresher(contentEl);
    } else if (!useNativeRefresher) {
      this.destroyNativeRefresher();
    }
  }

  private destroyNativeRefresher() {
    if (this.scrollEl && this.scrollListenerCallback) {
      this.scrollEl.removeEventListener('scroll', this.scrollListenerCallback);
      this.scrollListenerCallback = undefined;
    }

    this.nativeRefresher = false;
  }

  private async resetNativeRefresher(el: HTMLElement | undefined, state: RefresherState) {
    this.state = state;

    if (getIonMode(this) === 'ios') {
      await translateElement(el, undefined, 300);
    } else {
      await transitionEndAsync(this.el.querySelector('.refresher-refreshing-icon'), 200);
    }

    this.didRefresh = false;
    this.needsCompletion = false;
    this.pointerDown = false;
    this.animations.forEach((ani) => ani.destroy());
    this.animations = [];
    this.progress = 0;

    this.state = RefresherState.Inactive;

    this.ionPullEnd.emit({
      reason: state === RefresherState.Completing ? 'complete' : 'cancel',
    });
  }

  private async setupiOSNativeRefresher(
    pullingSpinner: HTMLIonSpinnerElement,
    refreshingSpinner: HTMLIonSpinnerElement
  ) {
    this.elementToTransform = this.scrollEl!;
    const ticks = pullingSpinner.shadowRoot!.querySelectorAll('svg');
    let MAX_PULL = this.scrollEl!.clientHeight * 0.16;
    const NUM_TICKS = ticks.length;

    writeTask(() => ticks.forEach((el) => el.style.setProperty('animation', 'none')));

    this.scrollListenerCallback = () => {
      // If pointer is not on screen or refresher is not active, ignore scroll
      if (!this.pointerDown && this.state === RefresherState.Inactive) {
        return;
      }

      readTask(() => {
        // PTR should only be active when overflow scrolling at the top
        const scrollTop = this.scrollEl!.scrollTop;
        const refresherHeight = this.el.clientHeight;

        if (scrollTop > 0) {
          /**
           * If refresher is refreshing and user tries to scroll
           * progressively fade refresher out/in
           */
          if (this.state === RefresherState.Refreshing) {
            const ratio = clamp(0, scrollTop / (refresherHeight * 0.5), 1);
            writeTask(() => setSpinnerOpacity(refreshingSpinner, 1 - ratio));
            return;
          }

          return;
        }

        if (this.pointerDown) {
          if (!this.didStart) {
            this.didStart = true;
            this.ionStart.emit();
            this.ionPullStart.emit();
          }

          // emit "pulling" on every move
          if (this.pointerDown) {
            this.ionPull.emit();
          }
        }

        /**
         * We want to delay the start of this gesture by ~30px
         * when initially pulling down so the refresher does not
         * overlap with the content. But when letting go of the
         * gesture before the refresher completes, we want the
         * refresher tick marks to quickly fade out.
         */
        const offset = this.didStart ? 30 : 0;
        const pullAmount = (this.progress = clamp(0, (Math.abs(scrollTop) - offset) / MAX_PULL, 1));
        const shouldShowRefreshingSpinner = this.state === RefresherState.Refreshing || pullAmount === 1;

        if (shouldShowRefreshingSpinner) {
          if (this.pointerDown) {
            handleScrollWhileRefreshing(refreshingSpinner, this.lastVelocityY);
          }

          if (!this.didRefresh) {
            this.beginRefresh();
            this.didRefresh = true;
            hapticImpact({ style: ImpactStyle.Light });

            /**
             * Clear focus from any active element to prevent scroll jumps
             * when the refresh completes
             */
            const activeElement = document.activeElement as HTMLElement;
            if (activeElement?.blur !== undefined) {
              activeElement.blur();
            }

            /**
             * Translate the content element otherwise when pointer is removed
             * from screen the scroll content will bounce back over the refresher
             */
            if (!this.pointerDown) {
              translateElement(this.elementToTransform, `${refresherHeight}px`);
            }
          }
        } else {
          this.state = RefresherState.Pulling;
          handleScrollWhilePulling(ticks, NUM_TICKS, pullAmount);
        }
      });
    };

    this.scrollEl!.addEventListener('scroll', this.scrollListenerCallback);

    this.gesture = (await import('../../utils/gesture')).createGesture({
      el: this.scrollEl!,
      gestureName: 'refresher',
      gesturePriority: 31,
      direction: 'y',
      threshold: 5,
      onStart: () => {
        this.pointerDown = true;

        if (!this.didRefresh) {
          translateElement(this.elementToTransform, '0px');
        }

        /**
         * If the content had `display: none` when
         * the refresher was initialized, its clientHeight
         * will be 0. When the gesture starts, the content
         * will be visible, so try to get the correct
         * client height again. This is most common when
         * using the refresher in an ion-menu.
         */
        if (MAX_PULL === 0) {
          MAX_PULL = this.scrollEl!.clientHeight * 0.16;
        }
      },
      onMove: (ev) => {
        this.lastVelocityY = ev.velocityY;
      },
      onEnd: () => {
        const hadStarted = this.didStart;
        this.pointerDown = false;
        this.didStart = false;

        if (this.needsCompletion) {
          this.resetNativeRefresher(this.elementToTransform, RefresherState.Completing);
          this.needsCompletion = false;
        } else if (this.didRefresh) {
          readTask(() => translateElement(this.elementToTransform, `${this.el.clientHeight}px`));
        } else if (hadStarted) {
          /**
           * User started pulling but released before reaching the refresh threshold.
           * Emit ionPullEnd to complete the event pair.
           */
          this.ionPullEnd.emit({ reason: 'cancel' });
        }
      },
    });

    this.disabledChanged();
  }

  private async setupMDNativeRefresher(
    contentEl: HTMLElement,
    pullingSpinner: HTMLIonSpinnerElement,
    refreshingSpinner: HTMLIonSpinnerElement
  ) {
    const circle = getElementRoot(pullingSpinner).querySelector('circle');
    const pullingRefresherIcon = this.el.querySelector('ion-refresher-content .refresher-pulling-icon') as HTMLElement;
    const refreshingCircle = getElementRoot(refreshingSpinner).querySelector('circle');

    if (circle !== null && refreshingCircle !== null) {
      writeTask(() => {
        circle.style.setProperty('animation', 'none');

        // This lines up the animation on the refreshing spinner with the pulling spinner
        refreshingSpinner.style.setProperty('animation-delay', '-655ms');
        refreshingCircle.style.setProperty('animation-delay', '-655ms');
      });
    }

    this.gesture = (await import('../../utils/gesture')).createGesture({
      el: this.scrollEl!,
      gestureName: 'refresher',
      gesturePriority: 31,
      direction: 'y',
      threshold: 5,
      canStart: () =>
        this.state !== RefresherState.Refreshing &&
        this.state !== RefresherState.Completing &&
        this.scrollEl!.scrollTop === 0,
      onStart: (ev: GestureDetail) => {
        this.progress = 0;

        ev.data = { animation: undefined, didStart: false, cancelled: false };
      },
      onMove: (ev: GestureDetail) => {
        if ((ev.velocityY < 0 && this.progress === 0 && !ev.data.didStart) || ev.data.cancelled) {
          ev.data.cancelled = true;
          return;
        }

        if (!ev.data.didStart) {
          ev.data.didStart = true;

          this.state = RefresherState.Pulling;

          // When ion-refresher is being used with a custom scroll target, the overflow styles need to be applied directly instead of via a css variable
          const { scrollEl } = this;
          const overflowProperty = scrollEl!.matches(ION_CONTENT_CLASS_SELECTOR) ? 'overflow' : '--overflow';
          writeTask(() => scrollEl!.style.setProperty(overflowProperty, 'hidden'));

          const animationType = getRefresherAnimationType(contentEl);
          const animation = createPullingAnimation(animationType, pullingRefresherIcon, this.el);
          ev.data.animation = animation;
          animation.progressStart(false, 0);
          this.ionStart.emit();
          this.ionPullStart.emit();
          this.animations.push(animation);

          return;
        }

        // Since we are using an easing curve, slow the gesture tracking down a bit
        this.progress = clamp(0, (ev.deltaY / 180) * 0.5, 1);
        ev.data.animation.progressStep(this.progress);
        this.ionPull.emit();
      },
      onEnd: (ev: GestureDetail) => {
        if (!ev.data.didStart) {
          return;
        }

        this.gesture!.enable(false);

        const { scrollEl } = this;
        const overflowProperty = scrollEl!.matches(ION_CONTENT_CLASS_SELECTOR) ? 'overflow' : '--overflow';
        writeTask(() => scrollEl!.style.removeProperty(overflowProperty));

        if (this.progress <= 0.4) {
          ev.data.animation.progressEnd(0, this.progress, 500).onFinish(() => {
            this.animations.forEach((ani) => ani.destroy());
            this.animations = [];
            this.gesture!.enable(true);
            this.state = RefresherState.Inactive;
            this.ionPullEnd.emit({ reason: 'cancel' });
          });
          return;
        }

        const progress = getTimeGivenProgression([0, 0], [0, 0], [1, 1], [1, 1], this.progress)[0];
        const snapBackAnimation = createSnapBackAnimation(pullingRefresherIcon);
        this.animations.push(snapBackAnimation);
        writeTask(async () => {
          pullingRefresherIcon.style.setProperty('--ion-pulling-refresher-translate', `${progress * 100}px`);
          ev.data.animation.progressEnd();
          await snapBackAnimation.play();
          this.beginRefresh();
          ev.data.animation.destroy();
          this.gesture!.enable(true);
        });
      },
    });

    this.disabledChanged();
  }

  private async setupNativeRefresher(contentEl: HTMLElement | null) {
    if (this.scrollListenerCallback || !contentEl || this.nativeRefresher || !this.scrollEl) {
      return;
    }

    /**
     * If using non-native refresher before make sure
     * we clean up any old CSS. This can happen when
     * a user manually calls the refresh method in a
     * component create callback before the native
     * refresher is setup.
     */
    this.setCss(0, '', false, '');

    this.nativeRefresher = true;

    const pullingSpinner = this.el.querySelector(
      'ion-refresher-content .refresher-pulling ion-spinner'
    ) as HTMLIonSpinnerElement;
    const refreshingSpinner = this.el.querySelector(
      'ion-refresher-content .refresher-refreshing ion-spinner'
    ) as HTMLIonSpinnerElement;

    if (getIonMode(this) === 'ios') {
      this.setupiOSNativeRefresher(pullingSpinner, refreshingSpinner);
    } else {
      this.setupMDNativeRefresher(contentEl, pullingSpinner, refreshingSpinner);
    }
  }

  componentDidUpdate() {
    this.checkNativeRefresher();
  }

  async connectedCallback() {
    if (this.el.getAttribute('slot') !== 'fixed') {
      printIonError('[ion-refresher] - Make sure you use: <ion-refresher slot="fixed">');
      return;
    }
    const contentEl = this.el.closest(ION_CONTENT_ELEMENT_SELECTOR);
    if (!contentEl) {
      printIonContentErrorMsg(this.el);
      return;
    }
    /**
     * Waits for the content to be ready before querying the scroll
     * or the background content element.
     */
    componentOnReady(contentEl, async () => {
      const customScrollTarget = contentEl.querySelector(ION_CONTENT_CLASS_SELECTOR);
      /**
       * Query the custom scroll target (if available), first. In refresher implementations,
       * the ion-refresher element will always be a direct child of ion-content (slot="fixed"). By
       * querying the custom scroll target first and falling back to the ion-content element,
       * the correct scroll element will be returned by the implementation.
       */
      this.scrollEl = await getScrollElement(customScrollTarget ?? contentEl);
      /**
       * Query the background content element from the host ion-content element directly.
       */
      this.backgroundContentEl = await contentEl.getBackgroundElement();
      /**
       * Check if the content element is fullscreen to apply the correct styles
       * when the refresher is refreshing. Otherwise, the refresher will be
       * hidden because it is positioned behind the background content element.
       */
      this.contentFullscreen = contentEl.fullscreen;

      if (await shouldUseNativeRefresher(this.el, getIonMode(this))) {
        this.setupNativeRefresher(contentEl);
      } else {
        this.gesture = (await import('../../utils/gesture')).createGesture({
          el: contentEl,
          gestureName: 'refresher',
          gesturePriority: 31,
          direction: 'y',
          threshold: 20,
          passive: false,
          canStart: () => this.canStart(),
          onStart: () => this.onStart(),
          onMove: (ev) => this.onMove(ev),
          onEnd: () => this.onEnd(),
        });

        this.disabledChanged();
      }
    });
  }

  disconnectedCallback() {
    this.destroyNativeRefresher();
    this.scrollEl = undefined;
    if (this.gesture) {
      this.gesture.destroy();
      this.gesture = undefined;
    }
  }

  /**
   * Call `complete()` when your async operation has completed.
   * For example, the `refreshing` state is while the app is performing
   * an asynchronous operation, such as receiving more data from an
   * AJAX request. Once the data has been received, you then call this
   * method to signify that the refreshing has completed and to close
   * the refresher. This method also changes the refresher's state from
   * `refreshing` to `completing`.
   */
  @Method()
  async complete() {
    if (this.nativeRefresher) {
      this.needsCompletion = true;

      // Do not reset scroll el until user removes pointer from screen
      if (!this.pointerDown) {
        raf(() => raf(() => this.resetNativeRefresher(this.elementToTransform, RefresherState.Completing)));
      }
    } else {
      this.close(RefresherState.Completing, '120ms');
    }
  }

  /**
   * Changes the refresher's state from `refreshing` to `cancelling`.
   */
  @Method()
  async cancel() {
    if (this.nativeRefresher) {
      // Do not reset scroll el until user removes pointer from screen
      if (!this.pointerDown) {
        raf(() => raf(() => this.resetNativeRefresher(this.elementToTransform, RefresherState.Cancelling)));
      }
    } else {
      this.close(RefresherState.Cancelling, '');
    }
  }

  /**
   * A number representing how far down the user has pulled.
   * The number `0` represents the user hasn't pulled down at all. The
   * number `1`, and anything greater than `1`, represents that the user
   * has pulled far enough down that when they let go then the refresh will
   * happen. If they let go and the number is less than `1`, then the
   * refresh will not happen, and the content will return to it's original
   * position.
   */
  @Method()
  getProgress() {
    return Promise.resolve(this.progress);
  }

  private canStart(): boolean {
    if (!this.scrollEl) {
      return false;
    }
    if (this.state !== RefresherState.Inactive) {
      return false;
    }
    // if the scrollTop is greater than zero then it's
    // not possible to pull the content down yet
    if (this.scrollEl.scrollTop > 0) {
      return false;
    }
    return true;
  }

  private onStart() {
    this.progress = 0;
    this.state = RefresherState.Inactive;
    this.memoizeOverflowStyle();

    /**
     * If the content is fullscreen, then we need to
     * set the offset-top style on the background content
     * element to ensure that the refresher is shown.
     */
    if (this.contentFullscreen && this.backgroundContentEl) {
      this.backgroundContentEl.style.setProperty('--offset-top', '0px');
    }
  }

  private onMove(detail: GestureDetail) {
    if (!this.scrollEl) {
      return;
    }
    // this method can get called like a bazillion times per second,
    // so it's built to be as efficient as possible, and does its
    // best to do any DOM read/writes only when absolutely necessary
    // if multi-touch then get out immediately
    const ev = detail.event as TouchEvent;
    if (ev.touches !== undefined && ev.touches.length > 1) {
      return;
    }

    // do nothing if it's actively refreshing
    // or it's in the way of closing
    // or this was never a startY
    if ((this.state & RefresherState._BUSY_) !== 0) {
      return;
    }

    const pullFactor = Number.isNaN(this.pullFactor) || this.pullFactor < 0 ? 1 : this.pullFactor;
    const deltaY = detail.deltaY * pullFactor;
    // don't bother if they're scrolling up
    // and have not already started dragging
    if (deltaY <= 0) {
      // the current Y is higher than the starting Y
      // so they scrolled up enough to be ignored
      this.progress = 0;
      this.state = RefresherState.Inactive;

      if (this.appliedStyles) {
        // reset the styles only if they were applied
        this.setCss(0, '', false, '');
        return;
      }

      return;
    }

    if (this.state === RefresherState.Inactive) {
      // this refresh is not already actively pulling down
      // get the content's scrollTop
      const scrollHostScrollTop = this.scrollEl.scrollTop;

      // if the scrollTop is greater than zero then it's
      // not possible to pull the content down yet
      if (scrollHostScrollTop > 0) {
        this.progress = 0;
        return;
      }

      // content scrolled all the way to the top, and dragging down
      this.state = RefresherState.Pulling;
    }

    // prevent native scroll events
    if (ev.cancelable) {
      ev.preventDefault();
    }

    // the refresher is actively pulling at this point
    // move the scroll element within the content element
    this.setCss(deltaY, '0ms', true, '');

    if (deltaY === 0) {
      // don't continue if there's no delta yet
      this.progress = 0;
      return;
    }

    const pullMin = this.pullMin;
    // set pull progress
    this.progress = deltaY / pullMin;

    // emit "start" if it hasn't started yet
    if (!this.didStart) {
      this.didStart = true;
      this.ionStart.emit();
      this.ionPullStart.emit();
    }

    // emit "pulling" on every move
    this.ionPull.emit();

    // do nothing if the delta is less than the pull threshold
    if (deltaY < pullMin) {
      // ensure it stays in the pulling state, cuz its not ready yet
      this.state = RefresherState.Pulling;
      return;
    }

    if (deltaY > this.pullMax) {
      // they pulled farther than the max, so kick off the refresh
      this.beginRefresh();
      return;
    }

    // pulled farther than the pull min!!
    // it is now in the `ready` state!!
    // if they let go then it'll refresh, kerpow!!
    this.state = RefresherState.Ready;

    return;
  }

  private onEnd() {
    // only run in a zone when absolutely necessary
    if (this.state === RefresherState.Ready) {
      // they pulled down far enough, so it's ready to refresh
      this.beginRefresh();
    } else if (this.state === RefresherState.Pulling) {
      // they were pulling down, but didn't pull down far enough
      // set the content back to it's original location
      // and close the refresher
      // set that the refresh is actively cancelling
      this.cancel();
    } else if (this.state === RefresherState.Inactive) {
      /**
       * The pull to refresh gesture was aborted
       * so we should immediately restore any overflow styles
       * that have been modified. Do not call this.cancel
       * because the styles will only be reset after a timeout.
       * If the gesture is aborted then scrolling should be
       * available right away.
       */
      this.restoreOverflowStyle();

      /**
       * If ionPullStart was emitted, we need to emit ionPullEnd
       * even though the gesture was aborted before reaching the
       * pulling threshold.
       */
      if (this.didStart) {
        this.didStart = false;
        this.ionPullEnd.emit({ reason: 'cancel' });
      }
    }
  }

  private beginRefresh() {
    // assumes we're already back in a zone
    // they pulled down far enough, so it's ready to refresh
    this.state = RefresherState.Refreshing;

    // place the content in a hangout position while it thinks
    this.setCss(this.pullMin, this.snapbackDuration, true, '');

    /**
     * Clear focus from any active element to prevent the browser
     * from restoring focus and causing scroll jumps after refresh.
     * This ensures the view stays at the top after refresh completes.
     */
    const activeElement = document.activeElement as HTMLElement;
    if (activeElement?.blur !== undefined) {
      activeElement.blur();
    }

    // emit "refresh" because it was pulled down far enough
    // and they let go to begin refreshing
    this.ionRefresh.emit({
      complete: this.complete.bind(this),
    });
  }

  private close(state: RefresherState, delay: string) {
    // create fallback timer incase something goes wrong with transitionEnd event
    setTimeout(() => {
      this.state = RefresherState.Inactive;
      this.progress = 0;
      this.didStart = false;

      /**
       * Reset any overflow styles so the
       * user can scroll again.
       */
      this.setCss(0, '0ms', false, '', true);

      /**
       * Reset the offset-top style on the background content
       * when the refresher is no longer refreshing and the
       * content is fullscreen.
       *
       * This ensures that the behavior of background content
       * does not change when refreshing is complete.
       */
      if (this.contentFullscreen && this.backgroundContentEl) {
        this.backgroundContentEl?.style.removeProperty('--offset-top');
      }

      this.ionPullEnd.emit({
        reason: state === RefresherState.Completing ? 'complete' : 'cancel',
      });
    }, 600);

    // reset the styles on the scroll element
    // set that the refresh is actively cancelling/completing
    this.state = state;
    this.setCss(0, this.closeDuration, true, delay);
  }

  private setCss(
    y: number,
    duration: string,
    overflowVisible: boolean,
    delay: string,
    shouldRestoreOverflowStyle = false
  ) {
    if (this.nativeRefresher) {
      return;
    }

    this.appliedStyles = y > 0;
    writeTask(() => {
      if (this.scrollEl && this.backgroundContentEl) {
        const scrollStyle = this.scrollEl.style;
        const backgroundStyle = this.backgroundContentEl.style;
        scrollStyle.transform = backgroundStyle.transform = y > 0 ? `translateY(${y}px) translateZ(0px)` : '';
        scrollStyle.transitionDuration = backgroundStyle.transitionDuration = duration;
        scrollStyle.transitionDelay = backgroundStyle.transitionDelay = delay;
        scrollStyle.overflow = overflowVisible ? 'hidden' : '';
      }

      /**
       * Reset the overflow styles only once
       * the pull to refresh effect has been closed.
       * This ensures that the gesture is done
       * and the refresh operation has either
       * been aborted or has completed.
       */
      if (shouldRestoreOverflowStyle) {
        this.restoreOverflowStyle();
      }
    });
  }

  private memoizeOverflowStyle() {
    if (this.scrollEl) {
      const { overflow, overflowX, overflowY } = this.scrollEl.style;
      this.overflowStyles = {
        overflow: overflow ?? '',
        overflowX: overflowX ?? '',
        overflowY: overflowY ?? '',
      };
    }
  }

  private restoreOverflowStyle() {
    if (this.overflowStyles !== undefined && this.scrollEl !== undefined) {
      const { overflow, overflowX, overflowY } = this.overflowStyles;
      this.scrollEl.style.overflow = overflow;
      this.scrollEl.style.overflowX = overflowX;
      this.scrollEl.style.overflowY = overflowY;

      this.overflowStyles = undefined;
    }
  }

  render() {
    const theme = getIonTheme(this);
    return (
      <Host
        slot="fixed"
        class={{
          [theme]: true,

          // Used internally for styling
          [`refresher-${theme}`]: true,
          'refresher-native': this.nativeRefresher,
          'refresher-active': this.state !== RefresherState.Inactive,
          'refresher-pulling': this.state === RefresherState.Pulling,
          'refresher-ready': this.state === RefresherState.Ready,
          'refresher-refreshing': this.state === RefresherState.Refreshing,
          'refresher-cancelling': this.state === RefresherState.Cancelling,
          'refresher-completing': this.state === RefresherState.Completing,
        }}
      ></Host>
    );
  }
}

const enum RefresherState {
  Inactive = 1 << 0,
  Pulling = 1 << 1,
  Ready = 1 << 2,
  Refreshing = 1 << 3,
  Cancelling = 1 << 4,
  Completing = 1 << 5,

  _BUSY_ = Refreshing | Cancelling | Completing,
}