joplin/packages/app-mobile/components/NoteBodyViewer/hooks/useSource.ts

import { useEffect, useState, useMemo, useRef } from 'react';
import shim from '@joplin/lib/shim';
import Setting from '@joplin/lib/models/Setting';
import { themeStyle } from '../../global-style';
import markupLanguageUtils from '@joplin/lib/markupLanguageUtils';
import useEditPopup from './useEditPopup';
import Logger from '@joplin/utils/Logger';
import { assetsToHeaders } from '@joplin/renderer';

const logger = Logger.create('NoteBodyViewer/useSource');

interface UseSourceResult {
	// [html] can be null if the note is still being rendered.
	html: string|null;
	injectedJs: string[];
}

function usePrevious(value: any, initialValue: any = null): any {
	const ref = useRef(initialValue);
	useEffect(() => {
		ref.current = value;
	});
	return ref.current;
}

const onlyCheckboxHasChangedHack = (previousBody: string, newBody: string) => {
	if (previousBody.length !== newBody.length) return false;

	for (let i = 0; i < previousBody.length; i++) {
		const c1 = previousBody.charAt(i);
		const c2 = newBody.charAt(i);

		if (c1 !== c2) {
			if (c1 === ' ' && (c2 === 'x' || c2 === 'X')) continue;
			if (c2 === ' ' && (c1 === 'x' || c1 === 'X')) continue;
			return false;
		}
	}

	return true;
};

export default function useSource(
	noteBody: string,
	noteMarkupLanguage: number,
	themeId: number,
	highlightedKeywords: string[],
	noteResources: any,
	paddingBottom: number,
	noteHash: string,
	initialScroll: number|null,
): UseSourceResult {
	const [html, setHtml] = useState<string>('');
	const [injectedJs, setInjectedJs] = useState<string[]>([]);
	const [resourceLoadedTime, setResourceLoadedTime] = useState(0);
	const [isFirstRender, setIsFirstRender] = useState(true);

	const paddingTop = '.8em';

	const rendererTheme = useMemo(() => {
		return {
			bodyPaddingTop: paddingTop, // Extra top padding on the rendered MD so it doesn't touch the border
			bodyPaddingBottom: paddingBottom, // Extra bottom padding to make it possible to scroll past the action button (so that it doesn't overlap the text)
			...themeStyle(themeId),
		};
	}, [themeId, paddingBottom]);

	const markupToHtml = useMemo(() => {
		return markupLanguageUtils.newMarkupToHtml();
		// eslint-disable-next-line @seiyab/react-hooks/exhaustive-deps -- Old code before rule was applied
	}, [isFirstRender]);

	// To address https://github.com/laurent22/joplin/issues/433
	//
	// If a checkbox in a note is ticked, the body changes, which normally would
	// trigger a re-render of this component, which has the unfortunate side
	// effect of making the view scroll back to the top. This re-rendering
	// however is unnecessary since the component is already visually updated via
	// JS. So here, if the note has not changed, we prevent the component from
	// updating. This fixes the above issue. A drawback of this is if the note
	// is updated via sync, this change will not be displayed immediately.
	//
	// 2022-05-03: However we sometimes need the HTML to be updated, even when
	// only the body has changed - for example when attaching a resource, or
	// when adding text via speech recognition. So the logic has been narrowed
	// down so that updates are skipped only when checkbox has been changed.
	// Checkboxes still work as expected, without making the note scroll, and
	// other text added to the note is displayed correctly.
	//
	// IMPORTANT: KEEP noteBody AS THE FIRST dependency in the array as the
	// below logic rely on this.
	const effectDependencies = [noteBody, resourceLoadedTime, noteMarkupLanguage, themeId, rendererTheme, highlightedKeywords, noteResources, noteHash, isFirstRender, markupToHtml];
	const previousDeps = usePrevious(effectDependencies, []);
	const changedDeps = effectDependencies.reduce((accum: any, dependency: any, index: any) => {
		if (dependency !== previousDeps[index]) {
			return { ...accum, [index]: true };
		}
		return accum;
	}, {});
	const onlyNoteBodyHasChanged = Object.keys(changedDeps).length === 1 && changedDeps[0];
	const onlyCheckboxesHaveChanged = previousDeps[0] && changedDeps[0] && onlyCheckboxHasChangedHack(previousDeps[0], noteBody);

	const { createEditPopupSyntax, destroyEditPopupSyntax, editPopupCss } = useEditPopup(themeId);

	useEffect(() => {
		if (onlyNoteBodyHasChanged && onlyCheckboxesHaveChanged) {
			logger.info('Only a checkbox has changed - not updating HTML');
			return () => {};
		}

		let cancelled = false;

		async function renderNote() {
			const theme = themeStyle(themeId);

			const bodyToRender = noteBody || '';

			const mdOptions = {
				onResourceLoaded: () => {
					setResourceLoadedTime(Date.now());
				},
				highlightedKeywords: highlightedKeywords,
				resources: noteResources,
				codeTheme: theme.codeThemeCss,
				postMessageSyntax: 'window.joplinPostMessage_',
				enableLongPress: true,

				// Show an 'edit' popup over SVG images
				editPopupFiletypes: ['image/svg+xml'],
				createEditPopupSyntax,
				destroyEditPopupSyntax,
			};

			// Whenever a resource state changes, for example when it goes from "not downloaded" to "downloaded", the "noteResources"
			// props changes, thus triggering a render. The **content** of this noteResources array however is not changed because
			// it doesn't contain info about the resource download state. Because of that, if we were to use the markupToHtml() cache
			// it wouldn't re-render at all. We don't need this cache in any way because this hook is only triggered when we know
			// something has changed.
			markupToHtml.clearCache(noteMarkupLanguage);

			const result = await markupToHtml.render(
				noteMarkupLanguage,
				bodyToRender,
				rendererTheme,
				mdOptions,
			);

			if (cancelled) return;

			let html = result.html;

			const resourceDownloadMode = Setting.value('sync.resourceDownloadMode');

			const js = [];
			js.push('try {');
			js.push(shim.injectedJs('webviewLib'));
			// Note that this postMessage function accepts two arguments, for compatibility with the desktop version, but
			// the ReactNativeWebView actually supports only one, so the second arg is ignored (and currently not needed for the mobile app).
			js.push('window.joplinPostMessage_ = (msg, args) => { return window.ReactNativeWebView.postMessage(msg); };');
			js.push('webviewLib.initialize({ postMessage: msg => { return window.ReactNativeWebView.postMessage(msg); } });');
			js.push(`
				const scrollingElement = document.scrollingElement;
				let lastScrollTop;
				const onMainContentScroll = () => {
					const newScrollTop = scrollingElement.scrollTop;
					if (lastScrollTop !== newScrollTop) {
						const eventData = { scrollTop: newScrollTop };
						window.ReactNativeWebView.postMessage('onscroll:' + JSON.stringify(eventData));
					}
				};

				// Listen for events on both scrollingElement and window
				// - On Android, scrollingElement.addEventListener('scroll', callback) doesn't call callback on
				// scroll. However, window.addEventListener('scroll', callback) does.
				// - iOS needs a listener to be added to scrollingElement -- events aren't received when
				//   the listener is added to window with window.addEventListener('scroll', ...).
				scrollingElement.addEventListener('scroll', onMainContentScroll);
				window.addEventListener('scroll', onMainContentScroll);

				const scrollContentToPosition = (position) => {
					scrollingElement.scrollTop = position;
				};
			`);
			js.push(`
				const readyStateCheckInterval = setInterval(function() {
					if (document.readyState === "complete") {
						clearInterval(readyStateCheckInterval);
						if ("${resourceDownloadMode}" === "manual") webviewLib.setupResourceManualDownload();

						const hash = "${noteHash}";
						const initialScroll = ${JSON.stringify(initialScroll)};

						// Don't scroll to a hash if we're given initial scroll (initial scroll
						// overrides scrolling to a hash).
						if ((initialScroll ?? null) !== null) {
							scrollContentToPosition(initialScroll);
					 	} else if (hash) {
							// Gives it a bit of time before scrolling to the anchor
							// so that images are loaded.
							setTimeout(() => { 
								const e = document.getElementById(hash);
								if (!e) {
									console.warn('Cannot find hash', hash);
									return;
								}
								e.scrollIntoView();
							}, 500);
						}
					}
				}, 10);
			`);
			js.push('} catch (e) {');
			js.push('	console.error(e);');
			js.push('	window.ReactNativeWebView.postMessage("error:" + e.message + ": " + JSON.stringify(e))');
			js.push('	true;');
			js.push('}');
			js.push('true;');

			// iOS doesn't automatically adjust the WebView's font size to match users'
			// accessibility settings. To do this, we need to tell it to match the system font.
			// See https://github.com/ionic-team/capacitor/issues/2748#issuecomment-612923135
			const iOSSpecificCss = `
				@media screen {
					:root body {
						font: -apple-system-body;
					}
				}
			`;
			const defaultCss = `
				code {
					white-space: pre-wrap;
					overflow-x: hidden;
				}

				body {
					padding-left: ${Number(theme.marginLeft)}px;
					padding-right: ${Number(theme.marginRight)}px;
				}
			`;

			html =
				`
				<!DOCTYPE html>
				<html>
					<head>
						<meta charset="UTF-8">
						<meta name="viewport" content="width=device-width, initial-scale=1">
						<style>
							${defaultCss}
							${shim.mobilePlatform() === 'ios' ? iOSSpecificCss : ''}
							${editPopupCss}
						</style>
						${assetsToHeaders(result.pluginAssets, { asHtml: true })}
					</head>
					<body>
						${html}
					</body>
				</html>
			`;

			setHtml(html);
			setInjectedJs(js);
		}

		// When mounted, we need to render the webview in two stages;
		// - First without any source, so that all webview props are setup properly
		// - Secondly with the source to actually render the note
		// This is necessary to prevent a race condition that could cause an ERR_ACCESS_DENIED error
		// https://github.com/react-native-webview/react-native-webview/issues/656#issuecomment-551312436

		if (isFirstRender) {
			setIsFirstRender(false);
			setHtml('');
			setInjectedJs([]);
		} else {
			void renderNote();
		}

		return () => {
			cancelled = true;
		};
		// eslint-disable-next-line @seiyab/react-hooks/exhaustive-deps -- Old code before rule was applied
	}, effectDependencies);

	return { html, injectedJs };
}