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Filename : wp-emoji-loader.js
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/**
 * @output wp-includes/js/wp-emoji-loader.js
 */

/* eslint-env es6 */

// Note: This is loaded as a script module, so there is no need for an IIFE to prevent pollution of the global scope.

/**
 * Emoji Settings as exported in PHP via _print_emoji_detection_script().
 * @typedef WPEmojiSettings
 * @type {object}
 * @property {?object} source
 * @property {?string} source.concatemoji
 * @property {?string} source.twemoji
 * @property {?string} source.wpemoji
 */

const settings = /** @type {WPEmojiSettings} */ (
	JSON.parse( document.getElementById( 'wp-emoji-settings' ).textContent )
);

// For compatibility with other scripts that read from this global, in particular wp-includes/js/wp-emoji.js (source file: js/_enqueues/wp/emoji.js).
window._wpemojiSettings = settings;

/**
 * Support tests.
 * @typedef SupportTests
 * @type {object}
 * @property {?boolean} flag
 * @property {?boolean} emoji
 */

const sessionStorageKey = 'wpEmojiSettingsSupports';
const tests = [ 'flag', 'emoji' ];

/**
 * Checks whether the browser supports offloading to a Worker.
 *
 * @since 6.3.0
 *
 * @private
 *
 * @returns {boolean}
 */
function supportsWorkerOffloading() {
	return (
		typeof Worker !== 'undefined' &&
		typeof OffscreenCanvas !== 'undefined' &&
		typeof URL !== 'undefined' &&
		URL.createObjectURL &&
		typeof Blob !== 'undefined'
	);
}

/**
 * @typedef SessionSupportTests
 * @type {object}
 * @property {number} timestamp
 * @property {SupportTests} supportTests
 */

/**
 * Get support tests from session.
 *
 * @since 6.3.0
 *
 * @private
 *
 * @returns {?SupportTests} Support tests, or null if not set or older than 1 week.
 */
function getSessionSupportTests() {
	try {
		/** @type {SessionSupportTests} */
		const item = JSON.parse(
			sessionStorage.getItem( sessionStorageKey )
		);
		if (
			typeof item === 'object' &&
			typeof item.timestamp === 'number' &&
			new Date().valueOf() < item.timestamp + 604800 && // Note: Number is a week in seconds.
			typeof item.supportTests === 'object'
		) {
			return item.supportTests;
		}
	} catch ( e ) {}
	return null;
}

/**
 * Persist the supports in session storage.
 *
 * @since 6.3.0
 *
 * @private
 *
 * @param {SupportTests} supportTests Support tests.
 */
function setSessionSupportTests( supportTests ) {
	try {
		/** @type {SessionSupportTests} */
		const item = {
			supportTests: supportTests,
			timestamp: new Date().valueOf()
		};

		sessionStorage.setItem(
			sessionStorageKey,
			JSON.stringify( item )
		);
	} catch ( e ) {}
}

/**
 * Checks if two sets of Emoji characters render the same visually.
 *
 * This is used to determine if the browser is rendering an emoji with multiple data points
 * correctly. set1 is the emoji in the correct form, using a zero-width joiner. set2 is the emoji
 * in the incorrect form, using a zero-width space. If the two sets render the same, then the browser
 * does not support the emoji correctly.
 *
 * This function may be serialized to run in a Worker. Therefore, it cannot refer to variables from the containing
 * scope. Everything must be passed by parameters.
 *
 * @since 4.9.0
 *
 * @private
 *
 * @param {CanvasRenderingContext2D} context 2D Context.
 * @param {string} set1 Set of Emoji to test.
 * @param {string} set2 Set of Emoji to test.
 *
 * @return {boolean} True if the two sets render the same.
 */
function emojiSetsRenderIdentically( context, set1, set2 ) {
	// Cleanup from previous test.
	context.clearRect( 0, 0, context.canvas.width, context.canvas.height );
	context.fillText( set1, 0, 0 );
	const rendered1 = new Uint32Array(
		context.getImageData(
			0,
			0,
			context.canvas.width,
			context.canvas.height
		).data
	);

	// Cleanup from previous test.
	context.clearRect( 0, 0, context.canvas.width, context.canvas.height );
	context.fillText( set2, 0, 0 );
	const rendered2 = new Uint32Array(
		context.getImageData(
			0,
			0,
			context.canvas.width,
			context.canvas.height
		).data
	);

	return rendered1.every( ( rendered2Data, index ) => {
		return rendered2Data === rendered2[ index ];
	} );
}

/**
 * Checks if the center point of a single emoji is empty.
 *
 * This is used to determine if the browser is rendering an emoji with a single data point
 * correctly. The center point of an incorrectly rendered emoji will be empty. A correctly
 * rendered emoji will have a non-zero value at the center point.
 *
 * This function may be serialized to run in a Worker. Therefore, it cannot refer to variables from the containing
 * scope. Everything must be passed by parameters.
 *
 * @since 6.8.2
 *
 * @private
 *
 * @param {CanvasRenderingContext2D} context 2D Context.
 * @param {string} emoji Emoji to test.
 *
 * @return {boolean} True if the center point is empty.
 */
function emojiRendersEmptyCenterPoint( context, emoji ) {
	// Cleanup from previous test.
	context.clearRect( 0, 0, context.canvas.width, context.canvas.height );
	context.fillText( emoji, 0, 0 );

	// Test if the center point (16, 16) is empty (0,0,0,0).
	const centerPoint = context.getImageData(16, 16, 1, 1);
	for ( let i = 0; i < centerPoint.data.length; i++ ) {
		if ( centerPoint.data[ i ] !== 0 ) {
			// Stop checking the moment it's known not to be empty.
			return false;
		}
	}

	return true;
}

/**
 * Determines if the browser properly renders Emoji that Twemoji can supplement.
 *
 * This function may be serialized to run in a Worker. Therefore, it cannot refer to variables from the containing
 * scope. Everything must be passed by parameters.
 *
 * @since 4.2.0
 *
 * @private
 *
 * @param {CanvasRenderingContext2D} context 2D Context.
 * @param {string} type Whether to test for support of "flag" or "emoji".
 * @param {Function} emojiSetsRenderIdentically Reference to emojiSetsRenderIdentically function, needed due to minification.
 * @param {Function} emojiRendersEmptyCenterPoint Reference to emojiRendersEmptyCenterPoint function, needed due to minification.
 *
 * @return {boolean} True if the browser can render emoji, false if it cannot.
 */
function browserSupportsEmoji( context, type, emojiSetsRenderIdentically, emojiRendersEmptyCenterPoint ) {
	let isIdentical;

	switch ( type ) {
		case 'flag':
			/*
			 * Test for Transgender flag compatibility. Added in Unicode 13.
			 *
			 * To test for support, we try to render it, and compare the rendering to how it would look if
			 * the browser doesn't render it correctly (white flag emoji + transgender symbol).
			 */
			isIdentical = emojiSetsRenderIdentically(
				context,
				'\uD83C\uDFF3\uFE0F\u200D\u26A7\uFE0F', // as a zero-width joiner sequence
				'\uD83C\uDFF3\uFE0F\u200B\u26A7\uFE0F' // separated by a zero-width space
			);

			if ( isIdentical ) {
				return false;
			}

			/*
			 * Test for Sark flag compatibility. This is the least supported of the letter locale flags,
			 * so gives us an easy test for full support.
			 *
			 * To test for support, we try to render it, and compare the rendering to how it would look if
			 * the browser doesn't render it correctly ([C] + [Q]).
			 */
			isIdentical = emojiSetsRenderIdentically(
				context,
				'\uD83C\uDDE8\uD83C\uDDF6', // as the sequence of two code points
				'\uD83C\uDDE8\u200B\uD83C\uDDF6' // as the two code points separated by a zero-width space
			);

			if ( isIdentical ) {
				return false;
			}

			/*
			 * Test for English flag compatibility. England is a country in the United Kingdom, it
			 * does not have a two letter locale code but rather a five letter sub-division code.
			 *
			 * To test for support, we try to render it, and compare the rendering to how it would look if
			 * the browser doesn't render it correctly (black flag emoji + [G] + [B] + [E] + [N] + [G]).
			 */
			isIdentical = emojiSetsRenderIdentically(
				context,
				// as the flag sequence
				'\uD83C\uDFF4\uDB40\uDC67\uDB40\uDC62\uDB40\uDC65\uDB40\uDC6E\uDB40\uDC67\uDB40\uDC7F',
				// with each code point separated by a zero-width space
				'\uD83C\uDFF4\u200B\uDB40\uDC67\u200B\uDB40\uDC62\u200B\uDB40\uDC65\u200B\uDB40\uDC6E\u200B\uDB40\uDC67\u200B\uDB40\uDC7F'
			);

			return ! isIdentical;
		case 'emoji':
			/*
			 * Is there a large, hairy, humanoid mythical creature living in the browser?
			 *
			 * To test for Emoji 17.0 support, try to render a new emoji: Hairy Creature.
			 *
			 * The hairy creature emoji is a single code point emoji. Testing for browser
			 * support required testing the center point of the emoji to see if it is empty.
			 *
			 * 0xD83E 0x1FAC8 (\uD83E\u1FAC8) == 🫈 Hairy creature.
			 *
			 * When updating this test, please ensure that the emoji is either a single code point
			 * or switch to using the emojiSetsRenderIdentically function and testing with a zero-width
			 * joiner vs a zero-width space.
			 */
			const notSupported = emojiRendersEmptyCenterPoint( context, '\uD83E\u1FAC8' );
			return ! notSupported;
	}

	return false;
}

/**
 * Checks emoji support tests.
 *
 * This function may be serialized to run in a Worker. Therefore, it cannot refer to variables from the containing
 * scope. Everything must be passed by parameters.
 *
 * @since 6.3.0
 *
 * @private
 *
 * @param {string[]} tests Tests.
 * @param {Function} browserSupportsEmoji Reference to browserSupportsEmoji function, needed due to minification.
 * @param {Function} emojiSetsRenderIdentically Reference to emojiSetsRenderIdentically function, needed due to minification.
 * @param {Function} emojiRendersEmptyCenterPoint Reference to emojiRendersEmptyCenterPoint function, needed due to minification.
 *
 * @return {SupportTests} Support tests.
 */
function testEmojiSupports( tests, browserSupportsEmoji, emojiSetsRenderIdentically, emojiRendersEmptyCenterPoint ) {
	let canvas;
	if (
		typeof WorkerGlobalScope !== 'undefined' &&
		self instanceof WorkerGlobalScope
	) {
		canvas = new OffscreenCanvas( 300, 150 ); // Dimensions are default for HTMLCanvasElement.
	} else {
		canvas = document.createElement( 'canvas' );
	}

	const context = canvas.getContext( '2d', { willReadFrequently: true } );

	/*
	 * Chrome on OS X added native emoji rendering in M41. Unfortunately,
	 * it doesn't work when the font is bolder than 500 weight. So, we
	 * check for bold rendering support to avoid invisible emoji in Chrome.
	 */
	context.textBaseline = 'top';
	context.font = '600 32px Arial';

	const supports = {};
	tests.forEach( ( test ) => {
		supports[ test ] = browserSupportsEmoji( context, test, emojiSetsRenderIdentically, emojiRendersEmptyCenterPoint );
	} );
	return supports;
}

/**
 * Adds a script to the head of the document.
 *
 * @ignore
 *
 * @since 4.2.0
 *
 * @param {string} src The url where the script is located.
 *
 * @return {void}
 */
function addScript( src ) {
	const script = document.createElement( 'script' );
	script.src = src;
	script.defer = true;
	document.head.appendChild( script );
}

settings.supports = {
	everything: true,
	everythingExceptFlag: true
};

// Obtain the emoji support from the browser, asynchronously when possible.
new Promise( ( resolve ) => {
	let supportTests = getSessionSupportTests();
	if ( supportTests ) {
		resolve( supportTests );
		return;
	}

	if ( supportsWorkerOffloading() ) {
		try {
			// Note that the functions are being passed as arguments due to minification.
			const workerScript =
				'postMessage(' +
				testEmojiSupports.toString() +
				'(' +
				[
					JSON.stringify( tests ),
					browserSupportsEmoji.toString(),
					emojiSetsRenderIdentically.toString(),
					emojiRendersEmptyCenterPoint.toString()
				].join( ',' ) +
				'));';
			const blob = new Blob( [ workerScript ], {
				type: 'text/javascript'
			} );
			const worker = new Worker( URL.createObjectURL( blob ), { name: 'wpTestEmojiSupports' } );
			worker.onmessage = ( event ) => {
				supportTests = event.data;
				setSessionSupportTests( supportTests );
				worker.terminate();
				resolve( supportTests );
			};
			return;
		} catch ( e ) {}
	}

	supportTests = testEmojiSupports( tests, browserSupportsEmoji, emojiSetsRenderIdentically, emojiRendersEmptyCenterPoint );
	setSessionSupportTests( supportTests );
	resolve( supportTests );
} )
	// Once the browser emoji support has been obtained from the session, finalize the settings.
	.then( ( supportTests ) => {
		/*
		 * Tests the browser support for flag emojis and other emojis, and adjusts the
		 * support settings accordingly.
		 */
		for ( const test in supportTests ) {
			settings.supports[ test ] = supportTests[ test ];

			settings.supports.everything =
				settings.supports.everything && settings.supports[ test ];

			if ( 'flag' !== test ) {
				settings.supports.everythingExceptFlag =
					settings.supports.everythingExceptFlag &&
					settings.supports[ test ];
			}
		}

		settings.supports.everythingExceptFlag =
			settings.supports.everythingExceptFlag &&
			! settings.supports.flag;

		// When the browser can not render everything we need to load a polyfill.
		if ( ! settings.supports.everything ) {
			const src = settings.source || {};

			if ( src.concatemoji ) {
				addScript( src.concatemoji );
			} else if ( src.wpemoji && src.twemoji ) {
				addScript( src.twemoji );
				addScript( src.wpemoji );
			}
		}
	} );