ios.transition.ts

import type { Animation } from '../../interface';
import { createAnimation } from '../animation/animation';
import type { TransitionOptions } from '../transition';
import { getIonPageElement } from '../transition';

const DURATION = 540;

// TODO(FW-2832): types

const getClonedElement = <T extends HTMLIonBackButtonElement | HTMLIonTitleElement>(tagName: string) => {
  return document.querySelector<T>(`${tagName}.ion-cloned-element`);
};

export const shadow = <T extends Element>(el: T): ShadowRoot | T => {
  return el.shadowRoot || el;
};

const getLargeTitle = (refEl: any) => {
  const tabs = refEl.tagName === 'ION-TABS' ? refEl : refEl.querySelector('ion-tabs');
  const query = 'ion-content ion-header:not(.header-collapse-condense-inactive) ion-title.title-large';

  if (tabs != null) {
    const activeTab = tabs.querySelector('ion-tab:not(.tab-hidden), .ion-page:not(.ion-page-hidden)');
    return activeTab != null ? activeTab.querySelector(query) : null;
  }

  return refEl.querySelector(query);
};

const getBackButton = (refEl: any, backDirection: boolean) => {
  const tabs = refEl.tagName === 'ION-TABS' ? refEl : refEl.querySelector('ion-tabs');
  let buttonsList = [];

  if (tabs != null) {
    const activeTab = tabs.querySelector('ion-tab:not(.tab-hidden), .ion-page:not(.ion-page-hidden)');
    if (activeTab != null) {
      buttonsList = activeTab.querySelectorAll('ion-buttons');
    }
  } else {
    buttonsList = refEl.querySelectorAll('ion-buttons');
  }

  for (const buttons of buttonsList) {
    const parentHeader = buttons.closest('ion-header');
    const activeHeader = parentHeader && !parentHeader.classList.contains('header-collapse-condense-inactive');
    const backButton = buttons.querySelector('ion-back-button');
    const buttonsCollapse = buttons.classList.contains('buttons-collapse');
    const startSlot = buttons.slot === 'start' || buttons.slot === '';

    if (backButton !== null && startSlot && ((buttonsCollapse && activeHeader && backDirection) || !buttonsCollapse)) {
      return backButton;
    }
  }

  return null;
};

const createLargeTitleTransition = (
  rootAnimation: Animation,
  rtl: boolean,
  backDirection: boolean,
  enteringEl: HTMLElement,
  leavingEl: HTMLElement | undefined
) => {
  const enteringBackButton = getBackButton(enteringEl, backDirection);
  const leavingLargeTitle = getLargeTitle(leavingEl);

  const enteringLargeTitle = getLargeTitle(enteringEl);
  const leavingBackButton = getBackButton(leavingEl, backDirection);

  const shouldAnimationForward = enteringBackButton !== null && leavingLargeTitle !== null && !backDirection;
  const shouldAnimationBackward = enteringLargeTitle !== null && leavingBackButton !== null && backDirection;

  if (shouldAnimationForward) {
    const leavingLargeTitleBox = leavingLargeTitle.getBoundingClientRect();
    const enteringBackButtonBox = enteringBackButton.getBoundingClientRect();

    const enteringBackButtonTextEl = shadow(enteringBackButton).querySelector('.button-text');

    // Text element not rendered if developers pass text="" to the back button
    const enteringBackButtonTextBox = enteringBackButtonTextEl?.getBoundingClientRect();

    const leavingLargeTitleTextEl = shadow(leavingLargeTitle).querySelector('.toolbar-title')!;
    const leavingLargeTitleTextBox = leavingLargeTitleTextEl.getBoundingClientRect();

    animateLargeTitle(
      rootAnimation,
      rtl,
      backDirection,
      leavingLargeTitle,
      leavingLargeTitleBox,
      leavingLargeTitleTextBox,
      enteringBackButtonBox,
      enteringBackButtonTextEl,
      enteringBackButtonTextBox
    );
    animateBackButton(
      rootAnimation,
      rtl,
      backDirection,
      enteringBackButton,
      enteringBackButtonBox,
      enteringBackButtonTextEl,
      enteringBackButtonTextBox,
      leavingLargeTitle,
      leavingLargeTitleTextBox
    );
  } else if (shouldAnimationBackward) {
    const enteringLargeTitleBox = enteringLargeTitle.getBoundingClientRect();
    const leavingBackButtonBox = leavingBackButton.getBoundingClientRect();

    const leavingBackButtonTextEl = shadow(leavingBackButton).querySelector('.button-text');

    // Text element not rendered if developers pass text="" to the back button
    const leavingBackButtonTextBox = leavingBackButtonTextEl?.getBoundingClientRect();

    const enteringLargeTitleTextEl = shadow(enteringLargeTitle).querySelector('.toolbar-title')!;
    const enteringLargeTitleTextBox = enteringLargeTitleTextEl.getBoundingClientRect();

    animateLargeTitle(
      rootAnimation,
      rtl,
      backDirection,
      enteringLargeTitle,
      enteringLargeTitleBox,
      enteringLargeTitleTextBox,
      leavingBackButtonBox,
      leavingBackButtonTextEl,
      leavingBackButtonTextBox
    );
    animateBackButton(
      rootAnimation,
      rtl,
      backDirection,
      leavingBackButton,
      leavingBackButtonBox,
      leavingBackButtonTextEl,
      leavingBackButtonTextBox,
      enteringLargeTitle,
      enteringLargeTitleTextBox
    );
  }

  return {
    forward: shouldAnimationForward,
    backward: shouldAnimationBackward,
  };
};

const animateBackButton = (
  rootAnimation: Animation,
  rtl: boolean,
  backDirection: boolean,
  backButtonEl: HTMLIonBackButtonElement,
  backButtonBox: DOMRect,
  backButtonTextEl: HTMLElement | null,
  backButtonTextBox: DOMRect | undefined,
  largeTitleEl: HTMLIonTitleElement,
  largeTitleTextBox: DOMRect
) => {
  const BACK_BUTTON_START_OFFSET = rtl ? `calc(100% - ${backButtonBox.right + 4}px)` : `${backButtonBox.left - 4}px`;

  const TEXT_ORIGIN_X = rtl ? 'right' : 'left';
  const ICON_ORIGIN_X = rtl ? 'left' : 'right';

  const CONTAINER_ORIGIN_X = rtl ? 'right' : 'left';
  let WIDTH_SCALE = 1;
  let HEIGHT_SCALE = 1;

  let TEXT_START_SCALE = `scale(${HEIGHT_SCALE})`;
  const TEXT_END_SCALE = 'scale(1)';

  if (backButtonTextEl && backButtonTextBox) {
    /**
     * When the title and back button texts match then they should overlap during the
     * page transition. If the texts do not match up then the back button text scale
     * adjusts to not perfectly match the large title text otherwise the proportions
     * will be incorrect. When the texts match we scale both the width and height to
     * account for font weight differences between the title and back button.
     */
    const doTitleAndButtonTextsMatch = backButtonTextEl.textContent?.trim() === largeTitleEl.textContent?.trim();
    WIDTH_SCALE = largeTitleTextBox.width / backButtonTextBox.width;
    /**
     * Subtract an offset to account for slight sizing/padding differences between the
     * title and the back button.
     */
    HEIGHT_SCALE = (largeTitleTextBox.height - LARGE_TITLE_SIZE_OFFSET) / backButtonTextBox.height;

    /**
     * Even though we set TEXT_START_SCALE to HEIGHT_SCALE above, we potentially need
     * to re-compute this here since the HEIGHT_SCALE may have changed.
     */
    TEXT_START_SCALE = doTitleAndButtonTextsMatch ? `scale(${WIDTH_SCALE}, ${HEIGHT_SCALE})` : `scale(${HEIGHT_SCALE})`;
  }

  const backButtonIconEl = shadow(backButtonEl).querySelector('ion-icon')!;
  const backButtonIconBox = backButtonIconEl.getBoundingClientRect();

  /**
   * We need to offset the container by the icon dimensions
   * so that the back button text aligns with the large title
   * text. Otherwise, the back button icon will align with the
   * large title text but the back button text will not.
   */
  const CONTAINER_START_TRANSLATE_X = rtl
    ? `${backButtonIconBox.width / 2 - (backButtonIconBox.right - backButtonBox.right)}px`
    : `${backButtonBox.left - backButtonIconBox.width / 2}px`;
  const CONTAINER_END_TRANSLATE_X = rtl ? `-${window.innerWidth - backButtonBox.right}px` : `${backButtonBox.left}px`;

  /**
   * Back button container should be
   * aligned to the top of the title container
   * so the texts overlap as the back button
   * text begins to fade in.
   */
  const CONTAINER_START_TRANSLATE_Y = `${largeTitleTextBox.top}px`;

  /**
   * The cloned back button should align exactly with the
   * real back button on the entering page otherwise there will
   * be a layout shift.
   */
  const CONTAINER_END_TRANSLATE_Y = `${backButtonBox.top}px`;

  /**
   * In the forward direction, the cloned back button
   * container should translate from over the large title
   * to over the back button. In the backward direction,
   * it should translate from over the back button to over
   * the large title.
   */
  const FORWARD_CONTAINER_KEYFRAMES = [
    { offset: 0, transform: `translate3d(${CONTAINER_START_TRANSLATE_X}, ${CONTAINER_START_TRANSLATE_Y}, 0)` },
    { offset: 1, transform: `translate3d(${CONTAINER_END_TRANSLATE_X}, ${CONTAINER_END_TRANSLATE_Y}, 0)` },
  ];
  const BACKWARD_CONTAINER_KEYFRAMES = [
    { offset: 0, transform: `translate3d(${CONTAINER_END_TRANSLATE_X}, ${CONTAINER_END_TRANSLATE_Y}, 0)` },
    { offset: 1, transform: `translate3d(${CONTAINER_START_TRANSLATE_X}, ${CONTAINER_START_TRANSLATE_Y}, 0)` },
  ];
  const CONTAINER_KEYFRAMES = backDirection ? BACKWARD_CONTAINER_KEYFRAMES : FORWARD_CONTAINER_KEYFRAMES;

  /**
   * In the forward direction, the text in the cloned back button
   * should start to be (roughly) the size of the large title
   * and then scale down to be the size of the actual back button.
   * The text should also translate, but that translate is handled
   * by the container keyframes.
   */
  const FORWARD_TEXT_KEYFRAMES = [
    { offset: 0, opacity: 0, transform: TEXT_START_SCALE },
    { offset: 1, opacity: 1, transform: TEXT_END_SCALE },
  ];
  const BACKWARD_TEXT_KEYFRAMES = [
    { offset: 0, opacity: 1, transform: TEXT_END_SCALE },
    { offset: 1, opacity: 0, transform: TEXT_START_SCALE },
  ];
  const TEXT_KEYFRAMES = backDirection ? BACKWARD_TEXT_KEYFRAMES : FORWARD_TEXT_KEYFRAMES;

  /**
   * The icon should scale in/out in the second
   * half of the animation. The icon should also
   * translate, but that translate is handled by the
   * container keyframes.
   */
  const FORWARD_ICON_KEYFRAMES = [
    { offset: 0, opacity: 0, transform: 'scale(0.6)' },
    { offset: 0.6, opacity: 0, transform: 'scale(0.6)' },
    { offset: 1, opacity: 1, transform: 'scale(1)' },
  ];
  const BACKWARD_ICON_KEYFRAMES = [
    { offset: 0, opacity: 1, transform: 'scale(1)' },
    { offset: 0.2, opacity: 0, transform: 'scale(0.6)' },
    { offset: 1, opacity: 0, transform: 'scale(0.6)' },
  ];
  const ICON_KEYFRAMES = backDirection ? BACKWARD_ICON_KEYFRAMES : FORWARD_ICON_KEYFRAMES;

  const enteringBackButtonTextAnimation = createAnimation();
  const enteringBackButtonIconAnimation = createAnimation();
  const enteringBackButtonAnimation = createAnimation();

  const clonedBackButtonEl = getClonedElement<HTMLIonBackButtonElement>('ion-back-button')!;

  const clonedBackButtonTextEl = shadow(clonedBackButtonEl).querySelector('.button-text')!;
  const clonedBackButtonIconEl = shadow(clonedBackButtonEl).querySelector('ion-icon')!;

  clonedBackButtonEl.text = backButtonEl.text;
  clonedBackButtonEl.mode = backButtonEl.mode;
  clonedBackButtonEl.icon = backButtonEl.icon;
  clonedBackButtonEl.color = backButtonEl.color;
  clonedBackButtonEl.disabled = backButtonEl.disabled;

  clonedBackButtonEl.style.setProperty('display', 'block');
  clonedBackButtonEl.style.setProperty('position', 'fixed');

  enteringBackButtonIconAnimation.addElement(clonedBackButtonIconEl);
  enteringBackButtonTextAnimation.addElement(clonedBackButtonTextEl);
  enteringBackButtonAnimation.addElement(clonedBackButtonEl);

  enteringBackButtonAnimation
    .beforeStyles({
      position: 'absolute',
      top: '0px',
      [CONTAINER_ORIGIN_X]: '0px',
    })
    /**
     * The write hooks must be set on this animation as it is guaranteed to run. Other
     * animations such as the back button text animation will not run if the back button
     * has no visible text.
     */
    .beforeAddWrite(() => {
      backButtonEl.style.setProperty('display', 'none');
      clonedBackButtonEl.style.setProperty(TEXT_ORIGIN_X, BACK_BUTTON_START_OFFSET);
    })
    .afterAddWrite(() => {
      backButtonEl.style.setProperty('display', '');
      clonedBackButtonEl.style.setProperty('display', 'none');
      clonedBackButtonEl.style.removeProperty(TEXT_ORIGIN_X);
    })
    .keyframes(CONTAINER_KEYFRAMES);

  enteringBackButtonTextAnimation
    .beforeStyles({
      'transform-origin': `${TEXT_ORIGIN_X} top`,
    })
    .keyframes(TEXT_KEYFRAMES);

  enteringBackButtonIconAnimation
    .beforeStyles({
      'transform-origin': `${ICON_ORIGIN_X} center`,
    })
    .keyframes(ICON_KEYFRAMES);

  rootAnimation.addAnimation([
    enteringBackButtonTextAnimation,
    enteringBackButtonIconAnimation,
    enteringBackButtonAnimation,
  ]);
};

const animateLargeTitle = (
  rootAnimation: Animation,
  rtl: boolean,
  backDirection: boolean,
  largeTitleEl: HTMLIonTitleElement,
  largeTitleBox: DOMRect,
  largeTitleTextBox: DOMRect,
  backButtonBox: DOMRect,
  backButtonTextEl: HTMLElement | null,
  backButtonTextBox: DOMRect | undefined
) => {
  /**
   * The horizontal transform origin for the large title
   */
  const ORIGIN_X = rtl ? 'right' : 'left';

  const TITLE_START_OFFSET = rtl ? `calc(100% - ${largeTitleBox.right}px)` : `${largeTitleBox.left}px`;

  /**
   * The cloned large should align exactly with the
   * real large title on the leaving page otherwise there will
   * be a layout shift.
   */
  const START_TRANSLATE_X = '0px';
  const START_TRANSLATE_Y = `${largeTitleBox.top}px`;

  /**
   * How much to offset the large title translation by.
   * This accounts for differences in sizing between the large
   * title and the back button due to padding and font weight.
   */
  const LARGE_TITLE_TRANSLATION_OFFSET = 8;
  let END_TRANSLATE_X = rtl
    ? `-${window.innerWidth - backButtonBox.right - LARGE_TITLE_TRANSLATION_OFFSET}px`
    : `${backButtonBox.x + LARGE_TITLE_TRANSLATION_OFFSET}px`;

  /**
   * How much to scale the large title up/down by.
   */
  let HEIGHT_SCALE = 0.5;

  /**
   * The large title always starts full size.
   */
  const START_SCALE = 'scale(1)';

  /**
   * By default, we don't worry about having the large title scaled to perfectly
   * match the back button because we don't know if the back button's text matches
   * the large title's text.
   */
  let END_SCALE = `scale(${HEIGHT_SCALE})`;

  // Text element not rendered if developers pass text="" to the back button
  if (backButtonTextEl && backButtonTextBox) {
    /**
     * The scaled title should (roughly) overlap the back button. This ensures that
     * the back button and title overlap during the animation. Note that since both
     * elements either fade in or fade out over the course of the animation, neither
     * element will be fully visible on top of the other. As a result, the overlap
     * does not need to be perfect, so approximate values are acceptable here.
     */
    END_TRANSLATE_X = rtl
      ? `-${window.innerWidth - backButtonTextBox.right - LARGE_TITLE_TRANSLATION_OFFSET}px`
      : `${backButtonTextBox.x - LARGE_TITLE_TRANSLATION_OFFSET}px`;

    /**
     * In the forward direction, the large title should start at its normal size and
     * then scale down to be (roughly) the size of the back button on the other view.
     * In the backward direction, the large title should start at (roughly) the size
     * of the back button and then scale up to its original size.
     * Note that since both elements either fade in or fade out over the course of the
     * animation, neither element will be fully visible on top of the other. As a result,
     * the overlap  does not need to be perfect, so approximate values are acceptable here.
     */

    /**
     * When the title and back button texts match then they should overlap during the
     * page transition. If the texts do not match up then the large title text scale
     * adjusts to not perfectly match the back button text otherwise the proportions
     * will be incorrect. When the texts match we scale both the width and height to
     * account for font weight differences between the title and back button.
     */
    const doTitleAndButtonTextsMatch = backButtonTextEl.textContent?.trim() === largeTitleEl.textContent?.trim();

    const WIDTH_SCALE = backButtonTextBox.width / largeTitleTextBox.width;
    HEIGHT_SCALE = backButtonTextBox.height / (largeTitleTextBox.height - LARGE_TITLE_SIZE_OFFSET);

    /**
     * Even though we set TEXT_START_SCALE to HEIGHT_SCALE above, we potentially need
     * to re-compute this here since the HEIGHT_SCALE may have changed.
     */
    END_SCALE = doTitleAndButtonTextsMatch ? `scale(${WIDTH_SCALE}, ${HEIGHT_SCALE})` : `scale(${HEIGHT_SCALE})`;
  }

  /**
   * The midpoints of the back button and the title should align such that the back
   * button and title appear to be centered with each other.
   */
  const backButtonMidPoint = backButtonBox.top + backButtonBox.height / 2;
  const titleMidPoint = (largeTitleBox.height * HEIGHT_SCALE) / 2;
  const END_TRANSLATE_Y = `${backButtonMidPoint - titleMidPoint}px`;

  const BACKWARDS_KEYFRAMES = [
    { offset: 0, opacity: 0, transform: `translate3d(${END_TRANSLATE_X}, ${END_TRANSLATE_Y}, 0) ${END_SCALE}` },
    { offset: 0.1, opacity: 0 },
    { offset: 1, opacity: 1, transform: `translate3d(${START_TRANSLATE_X}, ${START_TRANSLATE_Y}, 0) ${START_SCALE}` },
  ];
  const FORWARDS_KEYFRAMES = [
    {
      offset: 0,
      opacity: 0.99,
      transform: `translate3d(${START_TRANSLATE_X}, ${START_TRANSLATE_Y}, 0) ${START_SCALE}`,
    },
    { offset: 0.6, opacity: 0 },
    { offset: 1, opacity: 0, transform: `translate3d(${END_TRANSLATE_X}, ${END_TRANSLATE_Y}, 0) ${END_SCALE}` },
  ];

  const KEYFRAMES = backDirection ? BACKWARDS_KEYFRAMES : FORWARDS_KEYFRAMES;

  const clonedTitleEl = getClonedElement<HTMLIonTitleElement>('ion-title')!;
  const clonedLargeTitleAnimation = createAnimation();

  clonedTitleEl.innerText = largeTitleEl.innerText;
  clonedTitleEl.size = largeTitleEl.size;
  clonedTitleEl.color = largeTitleEl.color;

  clonedLargeTitleAnimation.addElement(clonedTitleEl);

  clonedLargeTitleAnimation
    .beforeStyles({
      'transform-origin': `${ORIGIN_X} top`,

      /**
       * Since font size changes will cause
       * the dimension of the large title to change
       * we need to set the cloned title height
       * equal to that of the original large title height.
       */
      height: `${largeTitleBox.height}px`,
      display: '',
      position: 'relative',
      [ORIGIN_X]: TITLE_START_OFFSET,
    })
    .beforeAddWrite(() => {
      largeTitleEl.style.setProperty('opacity', '0');
    })
    .afterAddWrite(() => {
      largeTitleEl.style.setProperty('opacity', '');
      clonedTitleEl.style.setProperty('display', 'none');
    })
    .keyframes(KEYFRAMES);

  rootAnimation.addAnimation(clonedLargeTitleAnimation);
};

export const iosTransitionAnimation = (navEl: HTMLElement, opts: TransitionOptions): Animation => {
  try {
    const EASING = 'cubic-bezier(0.32,0.72,0,1)';
    const OPACITY = 'opacity';
    const TRANSFORM = 'transform';
    const CENTER = '0%';
    const OFF_OPACITY = 0.8;

    const isRTL = navEl.ownerDocument.dir === 'rtl';
    const OFF_RIGHT = isRTL ? '-99.5%' : '99.5%';
    const OFF_LEFT = isRTL ? '33%' : '-33%';

    const enteringEl = opts.enteringEl;
    const leavingEl = opts.leavingEl;

    const backDirection = opts.direction === 'back';
    const contentEl = enteringEl.querySelector(':scope > ion-content');
    const headerEls = enteringEl.querySelectorAll(':scope > ion-header > *:not(ion-toolbar), :scope > ion-footer > *');
    const enteringToolBarEls = enteringEl.querySelectorAll(':scope > ion-header > ion-toolbar');

    const rootAnimation = createAnimation();
    const enteringContentAnimation = createAnimation();

    rootAnimation
      .addElement(enteringEl)
      .duration((opts.duration ?? 0) || DURATION)
      .easing(opts.easing || EASING)
      .fill('both')
      .beforeRemoveClass('ion-page-invisible');

    // eslint-disable-next-line @typescript-eslint/prefer-optional-chain
    if (leavingEl && navEl !== null && navEl !== undefined) {
      const navDecorAnimation = createAnimation();
      navDecorAnimation.addElement(navEl);
      rootAnimation.addAnimation(navDecorAnimation);
    }

    if (!contentEl && enteringToolBarEls.length === 0 && headerEls.length === 0) {
      enteringContentAnimation.addElement(
        enteringEl.querySelector(':scope > .ion-page, :scope > ion-nav, :scope > ion-tabs')!
      ); // REVIEW
    } else {
      enteringContentAnimation.addElement(contentEl!); // REVIEW
      enteringContentAnimation.addElement(headerEls);
    }

    rootAnimation.addAnimation(enteringContentAnimation);

    if (backDirection) {
      enteringContentAnimation
        .beforeClearStyles([OPACITY])
        .fromTo('transform', `translateX(${OFF_LEFT})`, `translateX(${CENTER})`)
        .fromTo(OPACITY, OFF_OPACITY, 1);
    } else {
      // entering content, forward direction
      enteringContentAnimation
        .beforeClearStyles([OPACITY])
        .fromTo('transform', `translateX(${OFF_RIGHT})`, `translateX(${CENTER})`);
    }

    if (contentEl) {
      const enteringTransitionEffectEl = shadow(contentEl).querySelector('.transition-effect');
      if (enteringTransitionEffectEl) {
        const enteringTransitionCoverEl = enteringTransitionEffectEl.querySelector('.transition-cover');
        const enteringTransitionShadowEl = enteringTransitionEffectEl.querySelector('.transition-shadow');

        const enteringTransitionEffect = createAnimation();
        const enteringTransitionCover = createAnimation();
        const enteringTransitionShadow = createAnimation();

        enteringTransitionEffect
          .addElement(enteringTransitionEffectEl)
          .beforeStyles({ opacity: '1', display: 'block' })
          .afterStyles({ opacity: '', display: '' });

        enteringTransitionCover
          .addElement(enteringTransitionCoverEl!) // REVIEW
          .beforeClearStyles([OPACITY])
          .fromTo(OPACITY, 0, 0.1);

        enteringTransitionShadow
          .addElement(enteringTransitionShadowEl!) // REVIEW
          .beforeClearStyles([OPACITY])
          .fromTo(OPACITY, 0.03, 0.7);

        enteringTransitionEffect.addAnimation([enteringTransitionCover, enteringTransitionShadow]);
        enteringContentAnimation.addAnimation([enteringTransitionEffect]);
      }
    }

    const enteringContentHasLargeTitle = enteringEl.querySelector('ion-header.header-collapse-condense');

    const { forward, backward } = createLargeTitleTransition(
      rootAnimation,
      isRTL,
      backDirection,
      enteringEl,
      leavingEl
    );
    enteringToolBarEls.forEach((enteringToolBarEl) => {
      const enteringToolBar = createAnimation();
      enteringToolBar.addElement(enteringToolBarEl);
      rootAnimation.addAnimation(enteringToolBar);

      const enteringTitle = createAnimation();
      enteringTitle.addElement(enteringToolBarEl.querySelector('ion-title')!); // REVIEW

      const enteringToolBarButtons = createAnimation();
      const buttons = Array.from(enteringToolBarEl.querySelectorAll('ion-buttons,[menuToggle]'));

      const parentHeader = enteringToolBarEl.closest('ion-header');
      const inactiveHeader = parentHeader?.classList.contains('header-collapse-condense-inactive');

      let buttonsToAnimate;
      if (backDirection) {
        buttonsToAnimate = buttons.filter((button) => {
          const isCollapseButton = button.classList.contains('buttons-collapse');
          return (isCollapseButton && !inactiveHeader) || !isCollapseButton;
        });
      } else {
        buttonsToAnimate = buttons.filter((button) => !button.classList.contains('buttons-collapse'));
      }

      enteringToolBarButtons.addElement(buttonsToAnimate);

      const enteringToolBarItems = createAnimation();
      enteringToolBarItems.addElement(
        enteringToolBarEl.querySelectorAll(':scope > *:not(ion-title):not(ion-buttons):not([menuToggle])')
      );

      const enteringToolBarBg = createAnimation();
      enteringToolBarBg.addElement(shadow(enteringToolBarEl).querySelector('.toolbar-background')!); // REVIEW

      const enteringBackButton = createAnimation();
      const backButtonEl = enteringToolBarEl.querySelector('ion-back-button');

      if (backButtonEl) {
        enteringBackButton.addElement(backButtonEl);
      }

      enteringToolBar.addAnimation([
        enteringTitle,
        enteringToolBarButtons,
        enteringToolBarItems,
        enteringToolBarBg,
        enteringBackButton,
      ]);
      enteringToolBarButtons.fromTo(OPACITY, 0.01, 1);
      enteringToolBarItems.fromTo(OPACITY, 0.01, 1);

      if (backDirection) {
        if (!inactiveHeader) {
          enteringTitle
            .fromTo('transform', `translateX(${OFF_LEFT})`, `translateX(${CENTER})`)
            .fromTo(OPACITY, 0.01, 1);
        }

        enteringToolBarItems.fromTo('transform', `translateX(${OFF_LEFT})`, `translateX(${CENTER})`);

        // back direction, entering page has a back button
        enteringBackButton.fromTo(OPACITY, 0.01, 1);
      } else {
        // entering toolbar, forward direction
        if (!enteringContentHasLargeTitle) {
          enteringTitle
            .fromTo('transform', `translateX(${OFF_RIGHT})`, `translateX(${CENTER})`)
            .fromTo(OPACITY, 0.01, 1);
        }

        enteringToolBarItems.fromTo('transform', `translateX(${OFF_RIGHT})`, `translateX(${CENTER})`);
        enteringToolBarBg.beforeClearStyles([OPACITY, 'transform']);

        const translucentHeader = parentHeader?.translucent;
        if (!translucentHeader) {
          enteringToolBarBg.fromTo(OPACITY, 0.01, 'var(--opacity)');
        } else {
          enteringToolBarBg.fromTo('transform', isRTL ? 'translateX(-100%)' : 'translateX(100%)', 'translateX(0px)');
        }

        // forward direction, entering page has a back button
        if (!forward) {
          enteringBackButton.fromTo(OPACITY, 0.01, 1);
        }

        if (backButtonEl && !forward) {
          const enteringBackBtnText = createAnimation();
          enteringBackBtnText
            .addElement(shadow(backButtonEl).querySelector('.button-text')!) // REVIEW
            .fromTo(`transform`, isRTL ? 'translateX(-100px)' : 'translateX(100px)', 'translateX(0px)');

          enteringToolBar.addAnimation(enteringBackBtnText);
        }
      }
    });

    // setup leaving view
    if (leavingEl) {
      const leavingContent = createAnimation();
      const leavingContentEl = leavingEl.querySelector(':scope > ion-content');
      const leavingToolBarEls = leavingEl.querySelectorAll(':scope > ion-header > ion-toolbar');
      const leavingHeaderEls = leavingEl.querySelectorAll(
        ':scope > ion-header > *:not(ion-toolbar), :scope > ion-footer > *'
      );

      if (!leavingContentEl && leavingToolBarEls.length === 0 && leavingHeaderEls.length === 0) {
        leavingContent.addElement(leavingEl.querySelector(':scope > .ion-page, :scope > ion-nav, :scope > ion-tabs')!); // REVIEW
      } else {
        leavingContent.addElement(leavingContentEl!); // REVIEW
        leavingContent.addElement(leavingHeaderEls);
      }

      rootAnimation.addAnimation(leavingContent);

      if (backDirection) {
        // leaving content, back direction
        leavingContent
          .beforeClearStyles([OPACITY])
          .fromTo('transform', `translateX(${CENTER})`, isRTL ? 'translateX(-100%)' : 'translateX(100%)');

        const leavingPage = getIonPageElement(leavingEl) as HTMLElement;
        rootAnimation.afterAddWrite(() => {
          if (rootAnimation.getDirection() === 'normal') {
            leavingPage.style.setProperty('display', 'none');
          }
        });
      } else {
        // leaving content, forward direction
        leavingContent
          .fromTo('transform', `translateX(${CENTER})`, `translateX(${OFF_LEFT})`)
          .fromTo(OPACITY, 1, OFF_OPACITY);
      }

      if (leavingContentEl) {
        const leavingTransitionEffectEl = shadow(leavingContentEl).querySelector('.transition-effect');

        if (leavingTransitionEffectEl) {
          const leavingTransitionCoverEl = leavingTransitionEffectEl.querySelector('.transition-cover');
          const leavingTransitionShadowEl = leavingTransitionEffectEl.querySelector('.transition-shadow');

          const leavingTransitionEffect = createAnimation();
          const leavingTransitionCover = createAnimation();
          const leavingTransitionShadow = createAnimation();

          leavingTransitionEffect
            .addElement(leavingTransitionEffectEl)
            .beforeStyles({ opacity: '1', display: 'block' })
            .afterStyles({ opacity: '', display: '' });

          leavingTransitionCover
            .addElement(leavingTransitionCoverEl!) // REVIEW
            .beforeClearStyles([OPACITY])
            .fromTo(OPACITY, 0.1, 0);

          leavingTransitionShadow
            .addElement(leavingTransitionShadowEl!) // REVIEW
            .beforeClearStyles([OPACITY])
            .fromTo(OPACITY, 0.7, 0.03);

          leavingTransitionEffect.addAnimation([leavingTransitionCover, leavingTransitionShadow]);
          leavingContent.addAnimation([leavingTransitionEffect]);
        }
      }

      leavingToolBarEls.forEach((leavingToolBarEl) => {
        const leavingToolBar = createAnimation();
        leavingToolBar.addElement(leavingToolBarEl);

        const leavingTitle = createAnimation();
        leavingTitle.addElement(leavingToolBarEl.querySelector('ion-title')!); // REVIEW

        const leavingToolBarButtons = createAnimation();
        const buttons = leavingToolBarEl.querySelectorAll('ion-buttons,[menuToggle]');

        const parentHeader = leavingToolBarEl.closest('ion-header');
        const inactiveHeader = parentHeader?.classList.contains('header-collapse-condense-inactive');

        const buttonsToAnimate = Array.from(buttons).filter((button) => {
          const isCollapseButton = button.classList.contains('buttons-collapse');
          return (isCollapseButton && !inactiveHeader) || !isCollapseButton;
        });

        leavingToolBarButtons.addElement(buttonsToAnimate);

        const leavingToolBarItems = createAnimation();
        const leavingToolBarItemEls = leavingToolBarEl.querySelectorAll(
          ':scope > *:not(ion-title):not(ion-buttons):not([menuToggle])'
        );
        if (leavingToolBarItemEls.length > 0) {
          leavingToolBarItems.addElement(leavingToolBarItemEls);
        }

        const leavingToolBarBg = createAnimation();
        leavingToolBarBg.addElement(shadow(leavingToolBarEl).querySelector('.toolbar-background')!); // REVIEW

        const leavingBackButton = createAnimation();
        const backButtonEl = leavingToolBarEl.querySelector('ion-back-button');
        if (backButtonEl) {
          leavingBackButton.addElement(backButtonEl);
        }

        leavingToolBar.addAnimation([
          leavingTitle,
          leavingToolBarButtons,
          leavingToolBarItems,
          leavingBackButton,
          leavingToolBarBg,
        ]);
        rootAnimation.addAnimation(leavingToolBar);

        // fade out leaving toolbar items
        leavingBackButton.fromTo(OPACITY, 0.99, 0);

        leavingToolBarButtons.fromTo(OPACITY, 0.99, 0);
        leavingToolBarItems.fromTo(OPACITY, 0.99, 0);

        if (backDirection) {
          if (!inactiveHeader) {
            // leaving toolbar, back direction
            leavingTitle
              .fromTo('transform', `translateX(${CENTER})`, isRTL ? 'translateX(-100%)' : 'translateX(100%)')
              .fromTo(OPACITY, 0.99, 0);
          }

          leavingToolBarItems.fromTo(
            'transform',
            `translateX(${CENTER})`,
            isRTL ? 'translateX(-100%)' : 'translateX(100%)'
          );
          leavingToolBarBg.beforeClearStyles([OPACITY, 'transform']);
          // leaving toolbar, back direction, and there's no entering toolbar
          // should just slide out, no fading out
          const translucentHeader = parentHeader?.translucent;
          if (!translucentHeader) {
            leavingToolBarBg.fromTo(OPACITY, 'var(--opacity)', 0);
          } else {
            leavingToolBarBg.fromTo('transform', 'translateX(0px)', isRTL ? 'translateX(-100%)' : 'translateX(100%)');
          }

          if (backButtonEl && !backward) {
            const leavingBackBtnText = createAnimation();
            leavingBackBtnText
              .addElement(shadow(backButtonEl).querySelector('.button-text')!) // REVIEW
              .fromTo('transform', `translateX(${CENTER})`, `translateX(${(isRTL ? -124 : 124) + 'px'})`);
            leavingToolBar.addAnimation(leavingBackBtnText);
          }
        } else {
          // leaving toolbar, forward direction
          if (!inactiveHeader) {
            leavingTitle
              .fromTo('transform', `translateX(${CENTER})`, `translateX(${OFF_LEFT})`)
              .fromTo(OPACITY, 0.99, 0)
              .afterClearStyles([TRANSFORM, OPACITY]);
          }

          leavingToolBarItems
            .fromTo('transform', `translateX(${CENTER})`, `translateX(${OFF_LEFT})`)
            .afterClearStyles([TRANSFORM, OPACITY]);

          leavingBackButton.afterClearStyles([OPACITY]);
          leavingTitle.afterClearStyles([OPACITY]);
          leavingToolBarButtons.afterClearStyles([OPACITY]);
        }
      });
    }

    return rootAnimation;
  } catch (err) {
    throw err;
  }
};

/**
 * The scale of the back button during the animation
 * is computed based on the scale of the large title
 * and vice versa. However, we need to account for slight
 * variations in the size of the large title due to
 * padding and font weight. This value should be used to subtract
 * a small amount from the large title height when computing scales
 * to get more accurate scale results.
 */
const LARGE_TITLE_SIZE_OFFSET = 10;