selectionobserver.ts

/**
 * @license Copyright (c) 2003-2024, CKSource Holding sp. z o.o. All rights reserved.
 * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
 */

/**
 * @module engine/view/observer/selectionobserver
 */

/* global setInterval, clearInterval */

import Observer from './observer.js';
import MutationObserver from './mutationobserver.js';
import { env } from '@ckeditor/ckeditor5-utils';
import { debounce, type DebouncedFunc } from 'lodash-es';

import type View from '../view.js';
import type DocumentSelection from '../documentselection.js';
import type DomConverter from '../domconverter.js';
import type Selection from '../selection.js';
import FocusObserver from './focusobserver.js';

type DomSelection = globalThis.Selection;

/**
 * Selection observer class observes selection changes in the document. If a selection changes on the document this
 * observer checks if the DOM selection is different from the {@link module:engine/view/document~Document#selection view selection}.
 * The selection observer fires {@link module:engine/view/document~Document#event:selectionChange} event only if
 * a selection change was the only change in the document and the DOM selection is different from the view selection.
 *
 * This observer also manages the {@link module:engine/view/document~Document#isSelecting} property of the view document.
 *
 * Note that this observer is attached by the {@link module:engine/view/view~View} and is available by default.
 */
export default class SelectionObserver extends Observer {
	/**
	 * Instance of the mutation observer. Selection observer calls
	 * {@link module:engine/view/observer/mutationobserver~MutationObserver#flush} to ensure that the mutations will be handled
	 * before the {@link module:engine/view/document~Document#event:selectionChange} event is fired.
	 */
	public readonly mutationObserver: MutationObserver;

	/**
	 * Instance of the focus observer. Focus observer calls
	 * {@link module:engine/view/observer/focusobserver~FocusObserver#flush} to mark the latest focus change as complete.
	 */
	public readonly focusObserver: FocusObserver;

	/**
	 * Reference to the view {@link module:engine/view/documentselection~DocumentSelection} object used to compare
	 * new selection with it.
	 */
	public readonly selection: DocumentSelection;

	/**
	 * Reference to the {@link module:engine/view/view~View#domConverter}.
	 */
	public readonly domConverter: DomConverter;

	/**
	 * A set of documents which have added `selectionchange` listener to avoid adding a listener twice to the same
	 * document.
	 */
	private readonly _documents: WeakSet<Document>;

	/**
	 * Fires debounced event `selectionChangeDone`. It uses `lodash#debounce` method to delay function call.
	 */
	private readonly _fireSelectionChangeDoneDebounced: DebouncedFunc<( data: ViewDocumentSelectionEventData ) => void>;

	/**
	 * When called, starts clearing the {@link #_loopbackCounter} counter in time intervals. When the number of selection
	 * changes exceeds a certain limit within the interval of time, the observer will not fire `selectionChange` but warn about
	 * possible infinite selection loop.
	 */
	private readonly _clearInfiniteLoopInterval: ReturnType<typeof setInterval>;

	/**
	 * Unlocks the `isSelecting` state of the view document in case the selection observer did not record this fact
	 * correctly (for whatever reason). It is a safeguard (paranoid check), that returns document to the normal state
	 * after a certain period of time (debounced, postponed by each selectionchange event).
	 */
	private readonly _documentIsSelectingInactivityTimeoutDebounced: DebouncedFunc<() => void>;

	/**
	 * Private property to check if the code does not enter infinite loop.
	 */
	private _loopbackCounter: number;

	constructor( view: View ) {
		super( view );

		this.mutationObserver = view.getObserver( MutationObserver );
		this.focusObserver = view.getObserver( FocusObserver );
		this.selection = this.document.selection;
		this.domConverter = view.domConverter;

		this._documents = new WeakSet();

		this._fireSelectionChangeDoneDebounced = debounce( data => {
			this.document.fire<ViewDocumentSelectionChangeDoneEvent>( 'selectionChangeDone', data );
		}, 200 );

		this._clearInfiniteLoopInterval = setInterval( () => this._clearInfiniteLoop(), 1000 );

		this._documentIsSelectingInactivityTimeoutDebounced = debounce( () => ( this.document.isSelecting = false ), 5000 );

		this._loopbackCounter = 0;
	}

	/**
	 * @inheritDoc
	 */
	public override observe( domElement: HTMLElement ): void {
		const domDocument = domElement.ownerDocument;

		const startDocumentIsSelecting = () => {
			this.document.isSelecting = true;

			// Let's activate the safety timeout each time the document enters the "is selecting" state.
			this._documentIsSelectingInactivityTimeoutDebounced();
		};

		const endDocumentIsSelecting = () => {
			if ( !this.document.isSelecting ) {
				return;
			}

			// Make sure that model selection is up-to-date at the end of selecting process.
			// Sometimes `selectionchange` events could arrive after the `mouseup` event and that selection could be already outdated.
			this._handleSelectionChange( null, domDocument );

			this.document.isSelecting = false;

			// The safety timeout can be canceled when the document leaves the "is selecting" state.
			this._documentIsSelectingInactivityTimeoutDebounced.cancel();
		};

		// The document has the "is selecting" state while the user keeps making (extending) the selection
		// (e.g. by holding the mouse button and moving the cursor). The state resets when they either released
		// the mouse button or interrupted the process by pressing or releasing any key.
		this.listenTo( domElement, 'selectstart', startDocumentIsSelecting, { priority: 'highest' } );

		this.listenTo( domElement, 'keydown', endDocumentIsSelecting, { priority: 'highest', useCapture: true } );
		this.listenTo( domElement, 'keyup', endDocumentIsSelecting, { priority: 'highest', useCapture: true } );

		// Add document-wide listeners only once. This method could be called for multiple editing roots.
		if ( this._documents.has( domDocument ) ) {
			return;
		}

		// This listener is using capture mode to make sure that selection is upcasted before any other
		// handler would like to check it and update (for example table multi cell selection).
		this.listenTo( domDocument, 'mouseup', endDocumentIsSelecting, { priority: 'highest', useCapture: true } );

		this.listenTo( domDocument, 'selectionchange', ( evt, domEvent ) => {
			// @if CK_DEBUG_TYPING // if ( ( window as any ).logCKETyping ) {
			// @if CK_DEBUG_TYPING // 	const domSelection = domDocument.defaultView!.getSelection();
			// @if CK_DEBUG_TYPING // 	console.group( '%c[SelectionObserver]%c selectionchange', 'color:green', ''
			// @if CK_DEBUG_TYPING // 	);
			// @if CK_DEBUG_TYPING // 	console.info( '%c[SelectionObserver]%c DOM Selection:', 'font-weight:bold;color:green', '',
			// @if CK_DEBUG_TYPING // 		{ node: domSelection!.anchorNode, offset: domSelection!.anchorOffset },
			// @if CK_DEBUG_TYPING // 		{ node: domSelection!.focusNode, offset: domSelection!.focusOffset }
			// @if CK_DEBUG_TYPING // 	);
			// @if CK_DEBUG_TYPING // }

			// The Renderer is disabled while composing on non-android browsers, so we can't update the view selection
			// because the DOM and view tree drifted apart. Position mapping could fail because of it.
			if ( this.document.isComposing && !env.isAndroid ) {
				// @if CK_DEBUG_TYPING // if ( ( window as any ).logCKETyping ) {
				// @if CK_DEBUG_TYPING // 	console.info( '%c[SelectionObserver]%c Selection change ignored (isComposing)',
				// @if CK_DEBUG_TYPING // 		'font-weight:bold;color:green', ''
				// @if CK_DEBUG_TYPING // 	);
				// @if CK_DEBUG_TYPING // 	console.groupEnd();
				// @if CK_DEBUG_TYPING // }

				return;
			}

			this._handleSelectionChange( domEvent, domDocument );

			// @if CK_DEBUG_TYPING // if ( ( window as any ).logCKETyping ) {
			// @if CK_DEBUG_TYPING // 	console.groupEnd();
			// @if CK_DEBUG_TYPING // }

			// Defer the safety timeout when the selection changes (e.g. the user keeps extending the selection
			// using their mouse).
			this._documentIsSelectingInactivityTimeoutDebounced();
		} );

		this._documents.add( domDocument );
	}

	/**
	 * @inheritDoc
	 */
	public override stopObserving( domElement: HTMLElement ): void {
		this.stopListening( domElement );
	}

	/**
	 * @inheritDoc
	 */
	public override destroy(): void {
		super.destroy();

		clearInterval( this._clearInfiniteLoopInterval );
		this._fireSelectionChangeDoneDebounced.cancel();
		this._documentIsSelectingInactivityTimeoutDebounced.cancel();
	}

	/* istanbul ignore next -- @preserve */
	private _reportInfiniteLoop() {
	// @if CK_DEBUG //		throw new Error(
	// @if CK_DEBUG //			'Selection change observer detected an infinite rendering loop.\n\n' +
	// @if CK_DEBUG //	 		'⚠️⚠️ Report this error on https://github.com/ckeditor/ckeditor5/issues/11658.'
	// @if CK_DEBUG //		);
	}

	/**
	 * Selection change listener. {@link module:engine/view/observer/mutationobserver~MutationObserver#flush Flush} mutations, check if
	 * a selection changes and fires {@link module:engine/view/document~Document#event:selectionChange} event on every change
	 * and {@link module:engine/view/document~Document#event:selectionChangeDone} when a selection stop changing.
	 *
	 * @param domEvent DOM event.
	 * @param domDocument DOM document.
	 */
	private _handleSelectionChange( domEvent: unknown, domDocument: Document ) {
		if ( !this.isEnabled ) {
			return;
		}

		const domSelection = domDocument.defaultView!.getSelection()!;

		if ( this.checkShouldIgnoreEventFromTarget( domSelection.anchorNode! ) ) {
			return;
		}

		// Ensure the mutation event will be before selection event on all browsers.
		this.mutationObserver.flush();

		const newViewSelection = this.domConverter.domSelectionToView( domSelection );

		// Do not convert selection change if the new view selection has no ranges in it.
		//
		// It means that the DOM selection is in some way incorrect. Ranges that were in the DOM selection could not be
		// converted to the view. This happens when the DOM selection was moved outside of the editable element.
		if ( newViewSelection.rangeCount == 0 ) {
			this.view.hasDomSelection = false;

			return;
		}

		this.view.hasDomSelection = true;

		// Mark the latest focus change as complete (we got new selection after the focus so the selection is in the focused element).
		this.focusObserver.flush();

		if ( this.selection.isEqual( newViewSelection ) && this.domConverter.isDomSelectionCorrect( domSelection ) ) {
			return;
		}

		// Ensure we are not in the infinite loop (#400).
		// This counter is reset each second. 60 selection changes in 1 second is enough high number
		// to be very difficult (impossible) to achieve using just keyboard keys (during normal editor use).
		if ( ++this._loopbackCounter > 60 ) {
			// Selection change observer detected an infinite rendering loop.
			// Most probably you try to put the selection in the position which is not allowed
			// by the browser and browser fixes it automatically what causes `selectionchange` event on
			// which a loopback through a model tries to re-render the wrong selection and again.
			this._reportInfiniteLoop();

			return;
		}

		if ( this.selection.isSimilar( newViewSelection ) ) {
			// If selection was equal and we are at this point of algorithm, it means that it was incorrect.
			// Just re-render it, no need to fire any events, etc.
			this.view.forceRender();
		} else {
			const data: ViewDocumentSelectionEventData = {
				oldSelection: this.selection,
				newSelection: newViewSelection,
				domSelection
			};

			// @if CK_DEBUG_TYPING // if ( ( window as any ).logCKETyping ) {
			// @if CK_DEBUG_TYPING // 	console.info( '%c[SelectionObserver]%c Fire selection change:',
			// @if CK_DEBUG_TYPING // 		'font-weight:bold;color:green', '',
			// @if CK_DEBUG_TYPING // 		newViewSelection.getFirstRange()
			// @if CK_DEBUG_TYPING // 	);
			// @if CK_DEBUG_TYPING // }

			// Prepare data for new selection and fire appropriate events.
			this.document.fire<ViewDocumentSelectionChangeEvent>( 'selectionChange', data );

			// Call `#_fireSelectionChangeDoneDebounced` every time when `selectionChange` event is fired.
			// This function is debounced what means that `selectionChangeDone` event will be fired only when
			// defined int the function time will elapse since the last time the function was called.
			// So `selectionChangeDone` will be fired when selection will stop changing.
			this._fireSelectionChangeDoneDebounced( data );
		}
	}

	/**
	 * Clears `SelectionObserver` internal properties connected with preventing infinite loop.
	 */
	private _clearInfiniteLoop(): void {
		this._loopbackCounter = 0;
	}
}

/**
 * The value of {@link ~ViewDocumentSelectionChangeEvent} and {@link ~ViewDocumentSelectionChangeDoneEvent} events.
 */
export type ViewDocumentSelectionEventData = {

	/**
	 * Old View selection which is {@link module:engine/view/document~Document#selection}.
	 */
	oldSelection: DocumentSelection;

	/**
	 * New View selection which is converted DOM selection.
	 */
	newSelection: Selection;

	/**
	 * Native DOM selection.
	 */
	domSelection: DomSelection | null;
};

/**
 * Fired when a selection has changed. This event is fired only when the selection change was the only change that happened
 * in the document, and the old selection is different then the new selection.
 *
 * Introduced by {@link module:engine/view/observer/selectionobserver~SelectionObserver}.
 *
 * Note that because {@link module:engine/view/observer/selectionobserver~SelectionObserver} is attached by the
 * {@link module:engine/view/view~View} this event is available by default.
 *
 * @see module:engine/view/observer/selectionobserver~SelectionObserver
 * @eventName module:engine/view/document~Document#selectionChange
 */
export type ViewDocumentSelectionChangeEvent = {
	name: 'selectionChange';
	args: [ ViewDocumentSelectionEventData ];
};

/**
 * Fired when selection stops changing.
 *
 * Introduced by {@link module:engine/view/observer/selectionobserver~SelectionObserver}.
 *
 * Note that because {@link module:engine/view/observer/selectionobserver~SelectionObserver} is attached by the
 * {@link module:engine/view/view~View} this event is available by default.
 *
 * @see module:engine/view/observer/selectionobserver~SelectionObserver
 * @eventName module:engine/view/document~Document#selectionChangeDone
 */
export type ViewDocumentSelectionChangeDoneEvent = {
	name: 'selectionChangeDone';
	args: [ ViewDocumentSelectionEventData ];
};