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

( function( window, document, settings ) {
	var src, ready, ii, tests;

	// Create a canvas element for testing native browser support of emoji.
	var canvas = document.createElement( 'canvas' );
	var context = canvas.getContext && canvas.getContext( '2d' );

	/**
	 * Checks if two sets of Emoji characters render the same visually.
	 *
	 * @since 4.9.0
	 *
	 * @private
	 *
	 * @param {number[]} set1 Set of Emoji character codes.
	 * @param {number[]} set2 Set of Emoji character codes.
	 *
	 * @return {boolean} True if the two sets render the same.
	 */
	function emojiSetsRenderIdentically( set1, set2 ) {
		var stringFromCharCode = String.fromCharCode;

		// Cleanup from previous test.
		context.clearRect( 0, 0, canvas.width, canvas.height );
		context.fillText( stringFromCharCode.apply( this, set1 ), 0, 0 );
		var rendered1 = canvas.toDataURL();

		// Cleanup from previous test.
		context.clearRect( 0, 0, canvas.width, canvas.height );
		context.fillText( stringFromCharCode.apply( this, set2 ), 0, 0 );
		var rendered2 = canvas.toDataURL();

		return rendered1 === rendered2;
	}

	/**
	 * Detects if the browser supports rendering emoji or flag emoji.
	 *
	 * Flag emoji are a single glyph made of two characters, so some browsers
	 * (notably, Firefox OS X) don't support them.
	 *
	 * @since 4.2.0
	 *
	 * @private
	 *
	 * @param {string} type Whether to test for support of "flag" or "emoji".
	 *
	 * @return {boolean} True if the browser can render emoji, false if it cannot.
	 */
	function browserSupportsEmoji( type ) {
		var isIdentical;

		if ( ! context || ! context.fillText ) {
			return false;
		}

		/*
		 * 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';

		switch ( type ) {
			case 'flag':
				/*
				 * Test for Transgender flag compatibility. This flag is shortlisted for the Emoji 13 spec,
				 * but has landed in Twemoji early, so we can add support for it, too.
				 *
				 * 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(
					[ 0x1F3F3, 0xFE0F, 0x200D, 0x26A7, 0xFE0F ],
					[ 0x1F3F3, 0xFE0F, 0x200B, 0x26A7, 0xFE0F ]
				);

				if ( isIdentical ) {
					return false;
				}

				/*
				 * Test for UN 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 ([U] + [N]).
				 */
				isIdentical = emojiSetsRenderIdentically(
					[ 0xD83C, 0xDDFA, 0xD83C, 0xDDF3 ],
					[ 0xD83C, 0xDDFA, 0x200B, 0xD83C, 0xDDF3 ]
				);

				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 an 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(
					[ 0xD83C, 0xDFF4, 0xDB40, 0xDC67, 0xDB40, 0xDC62, 0xDB40, 0xDC65, 0xDB40, 0xDC6E, 0xDB40, 0xDC67, 0xDB40, 0xDC7F ],
					[ 0xD83C, 0xDFF4, 0x200B, 0xDB40, 0xDC67, 0x200B, 0xDB40, 0xDC62, 0x200B, 0xDB40, 0xDC65, 0x200B, 0xDB40, 0xDC6E, 0x200B, 0xDB40, 0xDC67, 0x200B, 0xDB40, 0xDC7F ]
				);

				return ! isIdentical;
			case 'emoji':
				/*
				 * Burning Love: Just a hunk, a hunk of burnin' love.
				 *
				 *  To test for Emoji 13.1 support, try to render a new emoji: Heart on Fire!
				 *
				 * The Heart on Fire emoji is a ZWJ sequence combining ❤️ Red Heart, a Zero Width Joiner and 🔥 Fire.
				 *
				 * 0x2764, 0xfe0f == Red Heart emoji.
				 * 0x200D == Zero-Width Joiner (ZWJ) that links the two code points for the new emoji or
				 * 0x200B == Zero-Width Space (ZWS) that is rendered for clients not supporting the new emoji.
				 * 0xD83D, 0xDD25 == Fire.
				 *
				 * When updating this test for future Emoji releases, ensure that individual emoji that make up the
				 * sequence come from older emoji standards.
				 */
				isIdentical = emojiSetsRenderIdentically(
					[0x2764, 0xfe0f, 0x200D, 0xD83D, 0xDD25],
					[0x2764, 0xfe0f, 0x200B, 0xD83D, 0xDD25]
				);

				return ! isIdentical;
		}

		return false;
	}

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

		script.src = src;
		script.defer = script.type = 'text/javascript';
		document.getElementsByTagName( 'head' )[0].appendChild( script );
	}

	tests = Array( 'flag', 'emoji' );

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

	/*
	 * Tests the browser support for flag emojis and other emojis, and adjusts the
	 * support settings accordingly.
	 */
	for( ii = 0; ii < tests.length; ii++ ) {
		settings.supports[ tests[ ii ] ] = browserSupportsEmoji( tests[ ii ] );

		settings.supports.everything = settings.supports.everything && settings.supports[ tests[ ii ] ];

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

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

	// Sets DOMReady to false and assigns a ready function to settings.
	settings.DOMReady = false;
	settings.readyCallback = function() {
		settings.DOMReady = true;
	};

	// When the browser can not render everything we need to load a polyfill.
	if ( ! settings.supports.everything ) {
		ready = function() {
			settings.readyCallback();
		};

		/*
		 * Cross-browser version of adding a dom ready event.
		 */
		if ( document.addEventListener ) {
			document.addEventListener( 'DOMContentLoaded', ready, false );
			window.addEventListener( 'load', ready, false );
		} else {
			window.attachEvent( 'onload', ready );
			document.attachEvent( 'onreadystatechange', function() {
				if ( 'complete' === document.readyState ) {
					settings.readyCallback();
				}
			} );
		}

		src = settings.source || {};

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

} )( window, document, window._wpemojiSettings );
