/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

import {chain, getScrollParent, isIOS, useLayoutEffect} from '@react-aria/utils';

interface PreventScrollOptions {
  /** Whether the scroll lock is disabled. */
  isDisabled?: boolean
}

// @ts-ignore
const visualViewport = typeof document !== 'undefined' && window.visualViewport;

// HTML input types that do not cause the software keyboard to appear.
const nonTextInputTypes = new Set([
  'checkbox',
  'radio',
  'range',
  'color',
  'file',
  'image',
  'button',
  'submit',
  'reset'
]);

// The number of active usePreventScroll calls. Used to determine whether to revert back to the original page style/scroll position
let preventScrollCount = 0;
let restore;

/**
 * Prevents scrolling on the document body on mount, and
 * restores it on unmount. Also ensures that content does not
 * shift due to the scrollbars disappearing.
 */
export function usePreventScroll(options: PreventScrollOptions = {}) {
  let {isDisabled} = options;

  useLayoutEffect(() => {
    if (isDisabled) {
      return;
    }

    preventScrollCount++;
    if (preventScrollCount === 1) {
      if (isIOS()) {
        restore = preventScrollMobileSafari();
      } else {
        restore = preventScrollStandard();
      }
    }

    return () => {
      preventScrollCount--;
      if (preventScrollCount === 0) {
        restore();
      }
    };
  }, [isDisabled]);
}

// For most browsers, all we need to do is set `overflow: hidden` on the root element, and
// add some padding to prevent the page from shifting when the scrollbar is hidden.
function preventScrollStandard() {
  return chain(
    setStyle(document.documentElement, 'paddingRight', `${window.innerWidth - document.documentElement.clientWidth}px`),
    setStyle(document.documentElement, 'overflow', 'hidden')
  );
}

// Mobile Safari is a whole different beast. Even with overflow: hidden,
// it still scrolls the page in many situations:
//
// 1. When the bottom toolbar and address bar are collapsed, page scrolling is always allowed.
// 2. When the keyboard is visible, the viewport does not resize. Instead, the keyboard covers part of
//    it, so it becomes scrollable.
// 3. When tapping on an input, the page always scrolls so that the input is centered in the visual viewport.
//    This may cause even fixed position elements to scroll off the screen.
// 4. When using the next/previous buttons in the keyboard to navigate between inputs, the whole page always
//    scrolls, even if the input is inside a nested scrollable element that could be scrolled instead.
//
// In order to work around these cases, and prevent scrolling without jankiness, we do a few things:
//
// 1. Prevent default on `touchmove` events that are not in a scrollable element. This prevents touch scrolling
//    on the window.
// 2. Set `overscroll-behavior: contain` on nested scrollable regions so they do not scroll the page when at
//    the top or bottom. Work around a bug where this does not work when the element does not actually overflow
//    by preventing default in a `touchmove` event.
// 3. Prevent default on `touchend` events on input elements and handle focusing the element ourselves.
// 4. When focusing an input, apply a transform to trick Safari into thinking the input is at the top
//    of the page, which prevents it from scrolling the page. After the input is focused, scroll the element
//    into view ourselves, without scrolling the whole page.
// 5. Offset the body by the scroll position using a negative margin and scroll to the top. This should appear the
//    same visually, but makes the actual scroll position always zero. This is required to make all of the
//    above work or Safari will still try to scroll the page when focusing an input.
// 6. As a last resort, handle window scroll events, and scroll back to the top. This can happen when attempting
//    to navigate to an input with the next/previous buttons that's outside a modal.
function preventScrollMobileSafari() {
  let scrollable: Element;
  let restoreScrollableStyles;
  let onTouchStart = (e: TouchEvent) => {
    // Store the nearest scrollable parent element from the element that the user touched.
    scrollable = getScrollParent(e.target as Element, true);
    if (scrollable === document.documentElement && scrollable === document.body) {
      return;
    }

    // Prevent scrolling up when at the top and scrolling down when at the bottom
    // of a nested scrollable area, otherwise mobile Safari will start scrolling
    // the window instead.
    if (scrollable instanceof HTMLElement && window.getComputedStyle(scrollable).overscrollBehavior === 'auto') {
      restoreScrollableStyles = setStyle(scrollable, 'overscrollBehavior', 'contain');
    }
  };

  let onTouchMove = (e: TouchEvent) => {
    // Prevent scrolling the window.
    if (!scrollable || scrollable === document.documentElement || scrollable === document.body) {
      e.preventDefault();
      return;
    }

    // overscroll-behavior should prevent scroll chaining, but currently does not
    // if the element doesn't actually overflow. https://bugs.webkit.org/show_bug.cgi?id=243452
    // This checks that both the width and height do not overflow, otherwise we might
    // block horizontal scrolling too. In that case, adding `touch-action: pan-x` to
    // the element will prevent vertical page scrolling. We can't add that automatically
    // because it must be set before the touchstart event.
    if (scrollable.scrollHeight === scrollable.clientHeight && scrollable.scrollWidth === scrollable.clientWidth) {
      e.preventDefault();
    }
  };

  let onTouchEnd = (e: TouchEvent) => {
    let target = e.target as HTMLElement;

    // Apply this change if we're not already focused on the target element
    if (willOpenKeyboard(target) && target !== document.activeElement) {
      e.preventDefault();
      setupStyles();

      // Apply a transform to trick Safari into thinking the input is at the top of the page
      // so it doesn't try to scroll it into view. When tapping on an input, this needs to
      // be done before the "focus" event, so we have to focus the element ourselves.
      target.style.transform = 'translateY(-2000px)';
      target.focus();
      requestAnimationFrame(() => {
        target.style.transform = '';
      });
    }

    if (restoreScrollableStyles) {
      restoreScrollableStyles();
    }
  };

  let onFocus = (e: FocusEvent) => {
    let target = e.target as HTMLElement;
    if (willOpenKeyboard(target)) {
      setupStyles();

      // Transform also needs to be applied in the focus event in cases where focus moves
      // other than tapping on an input directly, e.g. the next/previous buttons in the
      // software keyboard. In these cases, it seems applying the transform in the focus event
      // is good enough, whereas when tapping an input, it must be done before the focus event. 🤷‍♂️
      target.style.transform = 'translateY(-2000px)';
      requestAnimationFrame(() => {
        target.style.transform = '';

        // This will have prevented the browser from scrolling the focused element into view,
        // so we need to do this ourselves in a way that doesn't cause the whole page to scroll.
        if (visualViewport) {
          if (visualViewport.height < window.innerHeight) {
            // If the keyboard is already visible, do this after one additional frame
            // to wait for the transform to be removed.
            requestAnimationFrame(() => {
              scrollIntoView(target);
            });
          } else {
            // Otherwise, wait for the visual viewport to resize before scrolling so we can
            // measure the correct position to scroll to.
            visualViewport.addEventListener('resize', () => scrollIntoView(target), {once: true});
          }
        }
      });
    }
  };

  let restoreStyles = null;
  let setupStyles = () => {
    if (restoreStyles) {
      return;
    }

    let onWindowScroll = () => {
      // Last resort. If the window scrolled, scroll it back to the top.
      // It should always be at the top because the body will have a negative margin (see below).
      window.scrollTo(0, 0);
    };

    // Record the original scroll position so we can restore it.
    // Then apply a negative margin to the body to offset it by the scroll position. This will
    // enable us to scroll the window to the top, which is required for the rest of this to work.
    let scrollX = window.pageXOffset;
    let scrollY = window.pageYOffset;

    restoreStyles = chain(
      addEvent(window, 'scroll', onWindowScroll),
      setStyle(document.documentElement, 'paddingRight', `${window.innerWidth - document.documentElement.clientWidth}px`),
      setStyle(document.documentElement, 'overflow', 'hidden'),
      setStyle(document.body, 'marginTop', `-${scrollY}px`),
      () => {
        window.scrollTo(scrollX, scrollY);
      }
    );

    // Scroll to the top. The negative margin on the body will make this appear the same.
    window.scrollTo(0, 0);
  };

  let removeEvents = chain(
    addEvent(document, 'touchstart', onTouchStart, {passive: false, capture: true}),
    addEvent(document, 'touchmove', onTouchMove, {passive: false, capture: true}),
    addEvent(document, 'touchend', onTouchEnd, {passive: false, capture: true}),
    addEvent(document, 'focus', onFocus, true)
  );

  return () => {
    // Restore styles and scroll the page back to where it was.
    restoreScrollableStyles?.();
    restoreStyles?.();
    removeEvents();
  };
}

// Sets a CSS property on an element, and returns a function to revert it to the previous value.
function setStyle(element: HTMLElement, style: string, value: string) {
  let cur = element.style[style];
  element.style[style] = value;

  return () => {
    element.style[style] = cur;
  };
}

// Adds an event listener to an element, and returns a function to remove it.
function addEvent<K extends keyof GlobalEventHandlersEventMap>(
  target: EventTarget,
  event: K,
  handler: (this: Document, ev: GlobalEventHandlersEventMap[K]) => any,
  options?: boolean | AddEventListenerOptions
) {
  target.addEventListener(event, handler, options);
  return () => {
    target.removeEventListener(event, handler, options);
  };
}

function scrollIntoView(target: Element) {
  let root = document.scrollingElement || document.documentElement;
  while (target && target !== root) {
    // Find the parent scrollable element and adjust the scroll position if the target is not already in view.
    let scrollable = getScrollParent(target);
    if (scrollable !== document.documentElement && scrollable !== document.body && scrollable !== target) {
      let scrollableTop = scrollable.getBoundingClientRect().top;
      let targetTop = target.getBoundingClientRect().top;
      if (targetTop > scrollableTop + target.clientHeight) {
        scrollable.scrollTop += targetTop - scrollableTop;
      }
    }

    target = scrollable.parentElement;
  }
}

function willOpenKeyboard(target: Element) {
  return (
    (target instanceof HTMLInputElement && !nonTextInputTypes.has(target.type)) ||
    target instanceof HTMLTextAreaElement ||
    (target instanceof HTMLElement && target.isContentEditable)
  );
}