( function ( mw, $ ) {

	var isSafari = navigator.userAgent.match( /Safari/ ) !== null,
		SIZES = {
			portraitImage: {
				h: 250, // Exact height
				w: 203 // Max width
			},
			landscapeImage: {
				h: 200, // Max height
				w: 300 // Exact Width
			},
			landscapePopupWidth: 450,
			portraitPopupWidth: 300,
			pokeySize: 8 // Height of the pokey.
		},
		$window = $( window );

	mw.popups.renderer = {};

	/**
	 * Extracted from `mw.popups.createSVGMasks`.
	 */
	function createPokeyMasks() {
		$( '<div>' )
			.attr( 'id', 'mwe-popups-svg' )
			.html(
				'<svg width="0" height="0">' +
					'<defs>' +
						'<clippath id="mwe-popups-mask">' +
							'<polygon points="0 8, 10 8, 18 0, 26 8, 1000 8, 1000 1000, 0 1000"/>' +
						'</clippath>' +
						'<clippath id="mwe-popups-mask-flip">' +
							'<polygon points="0 8, 274 8, 282 0, 290 8, 1000 8, 1000 1000, 0 1000"/>' +
						'</clippath>' +
						'<clippath id="mwe-popups-landscape-mask">' +
							'<polygon points="0 8, 174 8, 182 0, 190 8, 1000 8, 1000 1000, 0 1000"/>' +
						'</clippath>' +
						'<clippath id="mwe-popups-landscape-mask-flip">' +
							'<polygon points="0 0, 1000 0, 1000 243, 190 243, 182 250, 174 243, 0 243"/>' +
						'</clippath>' +
					'</defs>' +
				'</svg>'
			)
			.appendTo( document.body );
	}

	/**
	 * Initializes the renderer.
	 */
	mw.popups.renderer.init = function () {
		createPokeyMasks();
	};

	/**
	 * The model of how a view is rendered, which is constructed from a response
	 * from the gateway.
	 *
	 * TODO: Rename `isTall` to `isPortrait`.
	 *
	 * @typedef {Object} ext.popups.Preview
	 * @property {jQuery} el
	 * @property {Boolean} hasThumbnail
	 * @property {Object} thumbnail
	 * @property {Boolean} isTall Sugar around
	 *  `preview.hasThumbnail && thumbnail.isTall`
	 */

	/**
	 * Renders a preview given data from the {@link gateway ext.popups.Gateway}.
	 * The preview is rendered and added to the DOM but will remain hidden until
	 * the `show` method is called.
	 *
	 * Previews are rendered at:
	 *
	 * # The position of the mouse when the user dwells on the link with their
	 *   mouse.
	 * # The centermost point of the link when the user dwells on the link with
	 *   their keboard or other assistive device.
	 *
	 * Since the content of the preview doesn't change but its position might, we
	 * distinguish between "rendering" - generating HTML from a MediaWiki API
	 * response - and "showing/hiding" - positioning the layout and changing its
	 * orientation, if necessary.
	 *
	 * @param {ext.popups.PreviewModel} model
	 * @return {ext.popups.Preview}
	 */
	mw.popups.renderer.render = function ( model ) {
		var preview = model.extract === undefined ? createEmptyPreview( model ) : createPreview( model );

		return {

			/**
			 * Shows the preview given an event representing the user's interaction
			 * with the active link, e.g. an instance of
			 * [MouseEvent](https://developer.mozilla.org/en/docs/Web/API/MouseEvent).
			 *
			 * See `show` for more detail.
			 *
			 * @param {Event} event
			 * @param {Object} boundActions The
			 *  [bound action creators](http://redux.js.org/docs/api/bindActionCreators.html)
			 *  that were (likely) created in [boot.js](./boot.js).
			 * @return {jQuery.Promise}
			 */
			show: function ( event, boundActions ) {
				return show( preview, event, boundActions );
			},

			/**
			 * Hides the preview.
			 *
			 * See `hide` for more detail.
			 *
			 * @return {jQuery.Promise}
			 */
			hide: function () {
				return hide( preview );
			}
		};
	};

	/**
	 * Creates an instance of the DTO backing a preview.
	 *
	 * @param {ext.popups.PreviewModel} model
	 * @return {ext.popups.Preview}
	 */
	function createPreview( model ) {
		var templateData,
			thumbnail = createThumbnail( model.thumbnail ),
			hasThumbnail = thumbnail !== null,

			// FIXME: This should probably be moved into the gateway as we'll soon be
			// fetching HTML from the API. See
			// https://phabricator.wikimedia.org/T141651 for more detail.
			extract = renderExtract( model.extract, model.title ),

			$el;

		templateData = $.extend( {}, model, {
			lastModifiedMsg: mw.msg( 'popups-last-edited', moment( model.lastModified ).fromNow() ),
			hasThumbnail: hasThumbnail
		} );

		$el = mw.template.get( 'ext.popups', 'preview.mustache' )
			.render( templateData );

		if ( hasThumbnail ) {
			$el.find( '.mwe-popups-discreet' ).append( thumbnail.el );
		}

		if ( extract.length ) {
			$el.find( '.mwe-popups-extract' ).append( extract );
		}

		return {
			el: $el,
			hasThumbnail: hasThumbnail,
			thumbnail: thumbnail,
			isTall: hasThumbnail && thumbnail.isTall
		};
	}

	/**
	 * Creates an instance of the DTO backing a preview. In this case the DTO
	 * represents a generic preview, which covers the following scenarios:
	 *
	 * * The page doesn't exist, i.e. the user hovered over a redlink or a
	 *   redirect to a page that doesn't exist.
	 * * The page doesn't have a viable extract.
	 *
	 * @param {ext.popups.PreviewModel} model
	 * @return {ext.popups.Preview}
	 */
	function createEmptyPreview( model ) {
		var templateData,
			$el;

		templateData = $.extend( {}, model, {
			extractMsg: mw.msg( 'popups-preview-no-preview' ),
			readMsg: mw.msg( 'popups-preview-footer-read' )
		} );

		$el = mw.template.get( 'ext.popups', 'preview-empty.mustache' )
			.render( templateData );

		return {
			el: $el,
			hasThumbnail: false,
			isTall: false
		};
	}

	/**
	 * Converts the extract into a list of elements, which correspond to fragments
	 * of the extract. Fragements that match the title verbatim are wrapped in a
	 * `<b>` element.
	 *
	 * Using the bolded elements of the extract of the page directly is covered by
	 * [T141651](https://phabricator.wikimedia.org/T141651).
	 *
	 * Extracted from `mw.popups.renderer.article.getProcessedElements`.
	 *
	 * @param {String} extract
	 * @param {String} title
	 * @return {Array}
	 */
	function renderExtract( extract, title ) {
		var regExp, escapedTitle,
			elements = [],
			boldIdentifier = '<bi-' + Math.random() + '>',
			snip = '<snip-' + Math.random() + '>';

		title = title.replace( /\s+/g, ' ' ).trim(); // Remove extra white spaces
		escapedTitle = mw.RegExp.escape( title ); // Escape RegExp elements
		regExp = new RegExp( '(^|\\s)(' + escapedTitle + ')(|$)', 'i' );

		// Remove text in parentheses along with the parentheses
		extract = extract.replace( /\s+/, ' ' ); // Remove extra white spaces

		// Make title bold in the extract text
		// As the extract is html escaped there can be no such string in it
		// Also, the title is escaped of RegExp elements thus can't have "*"
		extract = extract.replace( regExp, '$1' + snip + boldIdentifier + '$2' + snip + '$3' );
		extract = extract.split( snip );

		$.each( extract, function ( index, part ) {
			if ( part.indexOf( boldIdentifier ) === 0 ) {
				elements.push( $( '<b>' ).text( part.substring( boldIdentifier.length ) ) );
			} else {
				elements.push( document.createTextNode( part ) );
			}
		} );

		return elements;
	}

	/**
	 * Shows the preview.
	 *
	 * Extracted from `mw.popups.render.openPopup`.
	 *
	 * TODO: From the perspective of the client, there's no need to distinguish
	 * between renderering and showing a preview. Merge #render and Preview#show.
	 *
	 * @param {ext.popups.Preview} preview
	 * @param {Event} event
	 * @param {ext.popups.PreviewBehavior} behavior
	 * @return {jQuery.Promise} A promise that resolves when the promise has faded
	 *  in
	 */
	function show( preview, event, behavior ) {
		var layout = createLayout( preview, event );

		preview.el.appendTo( document.body );

		// Hack to "refresh" the SVG so that it's displayed.
		//
		// Elements get added to the DOM and not to the screen because of different
		// namespaces of HTML and SVG.
		//
		// See http://stackoverflow.com/a/13654655/366138 for more detail.
		//
		// TODO: Find out how early on in the render that this could be done, e.g.
		// createThumbnail?
		preview.el.html( preview.el.html() );

		layoutPreview( preview, layout );

		preview.el.hover( behavior.previewDwell, behavior.previewAbandon );

		preview.el.find( '.mwe-popups-settings-icon' )
			.attr( 'href', behavior.settingsUrl )
			.click( behavior.showSettings );

		preview.el.show();

		return mw.popups.wait( 200 )
			.then( behavior.previewShow );
	}

	/**
	 * Extracted from `mw.popups.render.closePopup`.
	 *
	 * @param {ext.popups.Preview} preview
	 * @return {jQuery.Promise} A promise that resolves when the preview has faded
	 *  out
	 */
	function hide( preview ) {
		var fadeInClass,
			fadeOutClass;

		// FIXME: This method clearly needs access to the layout of the preview.
		fadeInClass = ( preview.el.hasClass( 'mwe-popups-fade-in-up' ) ) ?
			'mwe-popups-fade-in-up' :
			'mwe-popups-fade-in-down';

		fadeOutClass = ( fadeInClass === 'mwe-popups-fade-in-up' ) ?
			'mwe-popups-fade-out-down' :
			'mwe-popups-fade-out-up';

		preview.el
			.removeClass( fadeInClass )
			.addClass( fadeOutClass );

		return mw.popups.wait( 150 ).then( function () {
			preview.el.remove();
		} );
	}

	/**
	 * @typedef {Object} ext.popups.Thumbnail
	 * @property {Element} el
	 * @property {Boolean} isTall Whether or not the thumbnail is portrait
	 */

	/**
	 * Creates a thumbnail from the representation of a thumbnail returned by the
	 * PageImages MediaWiki API query module.
	 *
	 * If there's no thumbnail, the thumbnail is too small, or the thumbnail's URL
	 * contains characters that could be used to perform an
	 * [XSS attack via CSS](https://www.owasp.org/index.php/Testing_for_CSS_Injection_(OTG-CLIENT-005)),
	 * then `null` is returned.
	 *
	 * Extracted from `mw.popups.renderer.article.createThumbnail`.
	 *
	 * @param {Object} rawThumbnail
	 * @return {ext.popups.Thumbnail|null}
	 */
	function createThumbnail( rawThumbnail ) {
		var tall, thumbWidth, thumbHeight,
			x, y, width, height, clipPath,
			devicePixelRatio = $.bracketedDevicePixelRatio();

		if ( !rawThumbnail ) {
			return null;
		}

		tall = rawThumbnail.width < rawThumbnail.height;
		thumbWidth = rawThumbnail.width / devicePixelRatio;
		thumbHeight = rawThumbnail.height / devicePixelRatio;

		if (
			// Image too small for landscape display
			( !tall && thumbWidth < SIZES.landscapeImage.w ) ||
			// Image too small for portrait display
			( tall && thumbHeight < SIZES.portraitImage.h ) ||
			// These characters in URL that could inject CSS and thus JS
			(
				rawThumbnail.source.indexOf( '\\' ) > -1 ||
				rawThumbnail.source.indexOf( '\'' ) > -1 ||
				rawThumbnail.source.indexOf( '\"' ) > -1
			)
		) {
			return null;
		}

		if ( tall ) {
			x = ( thumbWidth > SIZES.portraitImage.w ) ?
				( ( thumbWidth - SIZES.portraitImage.w ) / -2 ) :
				( SIZES.portraitImage.w - thumbWidth );
			y = ( thumbHeight > SIZES.portraitImage.h ) ?
				( ( thumbHeight - SIZES.portraitImage.h ) / -2 ) : 0;
			width = SIZES.portraitImage.w;
			height = SIZES.portraitImage.h;
		} else {
			x = 0;
			y = ( thumbHeight > SIZES.landscapeImage.h ) ?
				( ( thumbHeight - SIZES.landscapeImage.h ) / -2 ) : 0;
			width = SIZES.landscapeImage.w + 3;
			height = ( thumbHeight > SIZES.landscapeImage.h ) ?
				SIZES.landscapeImage.h : thumbHeight;
			clipPath = 'mwe-popups-mask';
		}

		return {
			el: createThumbnailElement(
				tall ? 'mwe-popups-is-tall' : 'mwe-popups-is-not-tall',
				rawThumbnail.source,
				x,
				y,
				thumbWidth,
				thumbHeight,
				width,
				height,
				clipPath
			),
			isTall: tall,
			width: thumbWidth,
			height: thumbHeight
		};
	}

	/**
	 * Creates the SVG image element that represents the thumbnail.
	 *
	 * This function is distinct from `createThumbnail` as it abstracts away some
	 * browser issues that are uncovered when manipulating elements across
	 * namespaces.
	 *
	 * @param {String} className
	 * @param {String} url
	 * @param {Number} x
	 * @param {Number} y
	 * @param {Number} thumbnailWidth
	 * @param {Number} thumbnailHeight
	 * @param {Number} width
	 * @param {Number} height
	 * @param {String} clipPath
	 * @return {jQuery}
	 */
	function createThumbnailElement( className, url, x, y, thumbnailWidth, thumbnailHeight, width, height, clipPath ) {
		var $thumbnailSVGImage, $thumbnail,
			ns = 'http://www.w3.org/2000/svg',

			// Use createElementNS to create the svg:image tag as jQuery uses
			// createElement instead. Some browsers mistakenly map the image tag to
			// img tag.
			svgElement = document.createElementNS( 'http://www.w3.org/2000/svg', 'image' );

		$thumbnailSVGImage = $( svgElement );
		$thumbnailSVGImage
			.addClass( className )
			.attr( {
				x: x,
				y: y,
				width: thumbnailWidth,
				height: thumbnailHeight,
				'clip-path': 'url(#' + clipPath + ')'
			} );

		// Certain browsers, e.g. IE9, will not correctly set attributes from
		// foreign namespaces using Element#setAttribute (see T134979). Apart from
		// Safari, all supported browsers can set them using Element#setAttributeNS
		// (see T134979).
		if ( isSafari ) {
			svgElement.setAttribute( 'xlink:href', url );
		} else {
			svgElement.setAttributeNS( ns, 'xlink:href', url );
		}
		$thumbnail = $( '<svg>' )
			.attr( {
				xmlns: ns,
				width: width,
				height: height
			} )
			.append( $thumbnailSVGImage );

		return $thumbnail;
	}

	/**
	 * Represents the layout of a preview, which consists of a position (`offset`)
	 * and whether or not the preview should be flipped horizontally or
	 * vertically (`flippedX` and `flippedY` respectively).
	 *
	 * @typedef {Object} ext.popups.PreviewLayout
	 * @property {Object} offset
	 * @property {Boolean} flippedX
	 * @property {Boolean} flippedY
	 */

	/**
	 * Extracted from `mw.popups.renderer.article.getOffset`.
	 *
	 * @param {ext.popups.Preview} preview
	 * @param {Object} event
	 * @return {ext.popups.PreviewLayout}
	 */
	function createLayout( preview, event ) {
		var flippedX = false,
			flippedY = false,
			link = $( event.target ),
			offsetTop = ( event.pageY ) ? // If it was a mouse event
				// Position according to mouse
				// Since client rectangles are relative to the viewport,
				// take scroll position into account.
				getClosestYPosition(
					event.pageY - $window.scrollTop(),
					link.get( 0 ).getClientRects(),
					false
				) + $window.scrollTop() + SIZES.pokeySize :
				// Position according to link position or size
				link.offset().top + link.height() + SIZES.pokeySize,
			clientTop = ( event.clientY ) ?
				event.clientY :
				offsetTop,
			offsetLeft = ( event.pageX ) ?
				event.pageX :
				link.offset().left;

		// X Flip
		if ( offsetLeft > ( $window.width() / 2 ) ) {
			offsetLeft += ( !event.pageX ) ? link.width() : 0;
			offsetLeft -= !preview.isTall ?
				SIZES.portraitPopupWidth :
				SIZES.landscapePopupWidth;
			flippedX = true;
		}

		if ( event.pageX ) {
			offsetLeft += ( flippedX ) ? 20 : -20;
		}

		// Y Flip
		if ( clientTop > ( $window.height() / 2 ) ) {
			flippedY = true;

			// Mirror the positioning of the preview when there's no "Y flip": rest
			// the pokey on the edge of the link's bounding rectangle. In this case
			// the edge is the top-most.
			offsetTop = link.offset().top - SIZES.pokeySize;

			// Change the Y position to the top of the link
			if ( event.pageY ) {
				// Since client rectangles are relative to the viewport,
				// take scroll position into account.
				offsetTop = getClosestYPosition(
					event.pageY - $window.scrollTop(),
					link.get( 0 ).getClientRects(),
					true
				) + $window.scrollTop();
			}
		}

		return {
			offset: {
				top: offsetTop,
				left: offsetLeft
			},
			flippedX: flippedX,
			flippedY: flippedY
		};
	}

	/**
	 * Generates a list of declarative CSS classes that represent the layout of
	 * the preview.
	 *
	 * @param {ext.popups.Preview} preview
	 * @param {ext.popups.PreviewLayout} layout
	 * @return {String[]}
	 */
	function getClasses( preview, layout ) {
		var classes = [];

		if ( layout.flippedY ) {
			classes.push( 'mwe-popups-fade-in-down' );
		} else {
			classes.push( 'mwe-popups-fade-in-up' );
		}

		if ( layout.flippedY && layout.flippedX ) {
			classes.push( 'flipped_x_y' );
		}

		if ( layout.flippedY && !layout.flippedX ) {
			classes.push( 'flipped_y' );
		}

		if ( layout.flippedX && !layout.flippedY ) {
			classes.push( 'flipped_x' );
		}

		if ( ( !preview.hasThumbnail || preview.isTall ) && !layout.flippedY ) {
			classes.push( 'mwe-popups-no-image-tri' );
		}

		if ( ( preview.hasThumbnail && !preview.isTall ) && !layout.flippedY ) {
			classes.push( 'mwe-popups-image-tri' );
		}

		if ( preview.isTall ) {
			classes.push( 'mwe-popups-is-tall' );
		} else {
			classes.push( 'mwe-popups-is-not-tall' );
		}

		return classes;
	}

	/**
	 * Lays out the preview given the layout.
	 *
	 * If the preview should be oriented differently, then the pokey is updated,
	 * e.g. if the preview should be flipped vertically, then the pokey is
	 * removed.
	 *
	 * If the thumbnail is landscape and isn't the full height of the thumbnail
	 * container, then pull the extract up to keep whitespace consistent across
	 * previews.
	 *
	 * @param {ext.popups.Preview} preview
	 * @param {ext.popups.PreviewLayout} layout
	 */
	function layoutPreview( preview, layout ) {
		var popup = preview.el,
			isTall = preview.isTall,
			hasThumbnail = preview.hasThumbnail,
			thumbnail = preview.thumbnail,
			flippedY = layout.flippedY,
			flippedX = layout.flippedX,
			offsetTop = layout.offset.top;

		if ( !flippedY && !isTall && hasThumbnail && thumbnail.height < SIZES.landscapeImage.h ) {
			$( '.mwe-popups-extract' ).css(
				'margin-top',
				thumbnail.height - SIZES.pokeySize
			);
		}

		popup.addClass( getClasses( preview, layout ).join( ' ' ) );

		if ( flippedY ) {
			offsetTop -= popup.outerHeight();
		}

		popup.css( {
			top: offsetTop,
			left: layout.offset.left + 'px'
		} );

		if ( flippedY && hasThumbnail ) {
			popup.find( 'image' )[ 0 ]
				.setAttribute( 'clip-path', '' );
		}

		if ( flippedY && flippedX && hasThumbnail && isTall ) {
			popup.find( 'image' )[ 0 ]
				.setAttribute( 'clip-path', 'url(#mwe-popups-landscape-mask-flip)' );
		}

		if ( flippedX && !flippedY && hasThumbnail && !isTall ) {
			popup.find( 'image' )[ 0 ]
				.setAttribute( 'clip-path', 'url(#mwe-popups-mask-flip)' );
		}

		if ( flippedX && !flippedY && hasThumbnail && isTall ) {
			popup.removeClass( 'mwe-popups-no-image-tri' )
				.find( 'image' )[ 0 ]
				.setAttribute( 'clip-path', 'url(#mwe-popups-landscape-mask)' );
		}
	}

	/**
	 * Given the rectangular box(es) find the 'y' boundary of the closest
	 * rectangle to the point 'y'. The point 'y' is the location of the mouse
	 * on the 'y' axis and the rectangular box(es) are the borders of the
	 * element over which the mouse is located. There will be more than one
	 * rectangle in case the element spans multiple lines.
	 *
	 * In the majority of cases the mouse pointer will be inside a rectangle.
	 * However, some browsers (i.e. Chrome) trigger a hover action even when
	 * the mouse pointer is just outside a bounding rectangle. That's why
	 * we need to look at all rectangles and not just the rectangle that
	 * encloses the point.
	 *
	 * @param {Number} y the point for which the closest location is being
	 *  looked for
	 * @param {ClientRectList} rects list of rectangles defined by four edges
	 * @param {Boolean} [isTop] should the resulting rectangle's top 'y'
	 *  boundary be returned. By default the bottom 'y' value is returned.
	 * @return {Number}
	 */
	function getClosestYPosition( y, rects, isTop ) {
		var result,
			deltaY,
			minY = null;

		$.each( rects, function ( i, rect ) {
			deltaY = Math.abs( y - rect.top + y - rect.bottom );

			if ( minY === null || minY > deltaY ) {
				minY = deltaY;
				// Make sure the resulting point is at or outside the rectangle
				// boundaries.
				result = ( isTop ) ? Math.floor( rect.top ) : Math.ceil( rect.bottom );
			}
		} );

		return result;
	}

}( mediaWiki, jQuery ) );