image-focus.js

/* Image-focus.js */
/* Written by Obormot, 15 February 2019 */
/* License: GPL (derivative work of https://www.pmwiki.org/wiki/Cookbook/ImgFocus ) */
/* Lightweight dependency-free JavaScript library for "click to focus/zoom" images in HTML web pages. Originally coded for Obormot.net / GreaterWrong.com. */

ImageFocus = {
	/****************/
	/* Configuration.
	 ****************/

	contentImagesSelector: [
		".markdownBody figure img"
	].join(", "),

	excludedContainerElementsSelector: [
		"a",
		"button",
		"figure.image-focus-not"
	].join(", "),

	imageGalleryInclusionTest: (image) => {
		return (   image.closest("#markdownBody") != null
				&& image.closest(".footnotes") == null
				&& image.classList.contains("page-thumbnail") == false);
	},

	shrinkRatio: 0.975,

	hideUITimerDuration: (GW.isMobile() ? 5000 : 3000),

	dropShadowFilterForImages: "drop-shadow(10px 10px 10px #000) drop-shadow(0 0 10px #444)",

	hoverCaptionWidth: 175,
	hoverCaptionHeight: 75,

	fullSizeImageLoadHoverDelay: 25,

	/*****************/
	/* Infrastructure.
	 *****************/

	imageFocusUIElementsSelector: [
		".slideshow-button",
		".help-overlay",
		".image-number",
		".caption"
	].join(", "),

	focusableImagesSelector: null,
	focusedImageSelector: null,
	galleryImagesSelector: null,

	hideUITimer: null,

	overlay: null,

	mouseLastMovedAt: 0,

	currentlyFocusedImage: null,
	
	imageInFocus: null,

	/************/
	/* Functions.
	 ************/

	setup: () => {
		GWLog("ImageFocus.setup", "image-focus.js", 1);

		//  Create the image focus overlay.
		ImageFocus.overlay = addUIElement(`<div id="image-focus-overlay">
			<div class="help-overlay">
				<p class="slideshow-help-text"><strong>Arrow keys:</strong> Next/previous image</p>
				<p><strong>Escape</strong> or <strong>click</strong>: Hide zoomed image</p>
				<p><strong>Space bar:</strong> Reset image size & position</p>
				<p><strong>Scroll</strong> to zoom in/out</p>
				<p>(When zoomed in, <strong>drag</strong> to pan;<br /><strong>double-click</strong> to reset size & position)</p>
			</div>
			<div class="image-number"></div>
			<div class="slideshow-buttons">
				<button type="button" class="slideshow-button previous" tabindex="-1" title="Previous image">
					${(GW.svg("chevron-left-solid"))}
				</button>
				<button type="button" class="slideshow-button next" tabindex="-1" title="Next image">
					${(GW.svg("chevron-right-solid"))}
				</button>
			</div>
			<div class="caption"></div>
			<div class="loading-spinner">
				${(GW.svg("circle-notch-light"))}
			</div>
		</div>`);

		//  On orientation change, reset the size & position.
		doWhenMatchMedia(GW.mediaQueries.portraitOrientation, "ImageFocus.resetFocusedImagePositionWhenOrientationChanges", (mediaQuery) => {
			requestAnimationFrame(ImageFocus.resetFocusedImagePosition);
		});

		//  Add click listeners to the buttons.
		ImageFocus.overlay.querySelectorAll(".slideshow-button").forEach(button => {
			button.addActivateEvent(ImageFocus.slideshowButtonClicked = (event) => {
				GWLog("ImageFocus.slideshowButtonClicked", "image-focus.js", 2);

				ImageFocus.focusNextImage(event.target.classList.contains("next"));
				ImageFocus.cancelImageFocusHideUITimer();
				event.target.blur();
			});
		});

		//	Add listeners to help overlay.
		let helpOverlay = ImageFocus.overlay.querySelector(".help-overlay");
		if (GW.isMobile()) {
			helpOverlay.addEventListener("click", (event) => {
				helpOverlay.classList.toggle("open");
			});
		} else {
			helpOverlay.addEventListener("mouseenter", (event) => {
				helpOverlay.classList.add("open");
			});
			helpOverlay.addEventListener("mouseleave", (event) => {
				helpOverlay.classList.remove("open");
			});
		}

		//  UI starts out hidden.
		ImageFocus.hideImageFocusUI();

		//	Selector-suffixing function.
		function suffixedSelector(selector, suffix) {
			return selector.split(", ").map(part => part + suffix).join(", ");
		}

		/*	Create auxiliary selectors by suffixing provided content images
			selector with appropriate classes.
		 */
		ImageFocus.focusableImagesSelector = suffixedSelector(ImageFocus.contentImagesSelector, ".focusable");
		ImageFocus.focusedImageSelector = suffixedSelector(ImageFocus.contentImagesSelector, ".focused");
		ImageFocus.galleryImagesSelector = suffixedSelector(ImageFocus.contentImagesSelector, ".gallery-image");

        //  Add handler to set up events for images in injected content.
        addContentInjectHandler(ImageFocus.processImagesOnContentInject = (eventInfo) => {
            GWLog("ImageFocus.processImagesOnContentInject", "image-focus.js", 2);

            ImageFocus.processImagesWithin(eventInfo.container);

			//	If this content is (or is being loaded into) the main page...
			if (eventInfo.document == document) {
				//  Count how many images there are in the page, and set the “… of X” label to that.
				ImageFocus.overlay.querySelector(".image-number").dataset.numberOfImages = document.querySelectorAll(ImageFocus.galleryImagesSelector).length;

				//  Accesskey-L starts the slideshow.
				(document.querySelector(ImageFocus.galleryImagesSelector)||{}).accessKey = "l";
			}

			//	Fire targets-processed event.
			GW.notificationCenter.fireEvent("ImageFocus.imagesDidProcessOnContentInject", {
				source: "ImageFocus.processImagesOnContentInject",
				container: eventInfo.container,
				document: eventInfo.document
			});
        }, "eventListeners");

		//	Add handler to focus image on hashchange event.
		GW.notificationCenter.addHandlerForEvent("GW.hashDidChange", (info) => {
			ImageFocus.focusImageSpecifiedByURL();
		});

        //  Fire setup-complete event.
		GW.notificationCenter.fireEvent("ImageFocus.setupDidComplete");
	},

	designateSmallImageIfNeeded: (image) => {
		let width = image.getAttribute("width");
		let height = image.getAttribute("height");
		if (   (   width  !== null
				&& height !== null)
			&& (   width  < ImageFocus.hoverCaptionWidth
				|| height < ImageFocus.hoverCaptionHeight))
			image.classList.add("small-image");
	},

	processImagesWithin: (container) => {
		GWLog("ImageFocus.processImagesWithin", "image-focus.js", 1);

		/*	Add ‘focusable’ class to all focusable images; add ‘gallery-image’
			class to all focusable images that are to be included in the main
			image gallery; add ‘small-image’ class to all images that are too
			small to show the usual “Click to enlarge” overlay.
		 */
		container.querySelectorAll(ImageFocus.contentImagesSelector).forEach(image => {
			if (image.closest(ImageFocus.excludedContainerElementsSelector))
				return;

			image.classList.add("focusable");

			if (ImageFocus.imageGalleryInclusionTest(image))
				image.classList.add("gallery-image");

			ImageFocus.designateSmallImageIfNeeded(image);
		});

		//  Add the listener to all focusable images.
		container.querySelectorAll(ImageFocus.focusableImagesSelector).forEach(image => {
			image.addEventListener("click", ImageFocus.imageClickedToFocus);
		});

		//	Add listeners to preload full-sized images.
		container.querySelectorAll(ImageFocus.focusableImagesSelector).forEach(image => {
			image.removeAnnotationLoadEvents = onEventAfterDelayDo(image, "mouseenter", ImageFocus.fullSizeImageLoadHoverDelay, (event) => {
				ImageFocus.preloadImage(image);
				image.removeAnnotationLoadEvents();
			}, {
				cancelOnEvents: [ "mouseleave" ]
			});
		});

		//  Wrap all focusable images in a span.
		container.querySelectorAll(ImageFocus.focusableImagesSelector).forEach(image => {
			wrapElement(image, "span.image-wrapper.focusable", { moveClasses: [ "small-image" ] });
		});
	},

	focusedImgSrcForImage: (image) => {
		let imageSrcURL = URLFromString(image.src);
		if (   imageSrcURL.hostname == "upload.wikimedia.org"
			&& imageSrcURL.pathname.includes("/thumb/")) {
			let parts = /(.+)thumb\/(.+)\/[^\/]+$/.exec(imageSrcURL.pathname);
			imageSrcURL.pathname = parts[1] + parts[2];
			return imageSrcURL.href;
		} else if (image.srcset > "") {
			return Array.from(image.srcset.matchAll(/(\S+?)\s+(\S+?)(,|$)/g)).sort((a, b) => {
				if (parseFloat(a[2]) < parseFloat(b[2]))
					return -1;
				if (parseFloat(a[2]) > parseFloat(b[2]))
					return 1;
				return 0;
			}).last[1];
		} else if (image.dataset.srcSizeFull > "") {
			return image.dataset.srcSizeFull;
		} else {
			return image.src;
		}
	},

	expectedDimensionsForImage: (image) => {
		let width = parseInt(image.getAttribute("data-image-width") ?? image.getAttribute("data-file-width") ?? image.getAttribute("width"));
		let height = parseInt(image.getAttribute("data-image-height") ?? image.getAttribute("data-file-height") ?? image.getAttribute("height"));
		return (width && height
				? { width: width, height: height }
				: null);
	},

	preloadImage: (image) => {
		doAjax({ location: ImageFocus.focusedImgSrcForImage(image) });
	},

	focusImage: (imageToFocus, scrollToImage = true) => {
		GWLog("ImageFocus.focusImage", "image-focus.js", 1);

		//	Show overlay.
		ImageFocus.enterImageFocus();

		//	Show UI.
		ImageFocus.unhideImageFocusUI();

		//	Unfocus currently focused image, if any.
		ImageFocus.unfocusImage();

		//	Focus new image.
		imageToFocus.classList.toggle("focused", true);

		/*	If the new image is part of the main image gallery (i.e., if we are
			in gallery mode, rather than single-image mode)...
		 */
		if (imageToFocus.classList.contains("gallery-image")) {
			//	Update slideshow state.
			let lastFocusedImage = document.querySelector("img.last-focused");
			if (lastFocusedImage) {
				lastFocusedImage.classList.remove("last-focused");
				lastFocusedImage.removeAttribute("accesskey");
			}

			//  Set state of next/previous buttons.
			let images = document.querySelectorAll(ImageFocus.galleryImagesSelector);
			let indexOfFocusedImage = ImageFocus.getIndexOfFocusedImage();
			ImageFocus.overlay.querySelector(".slideshow-button.previous").disabled = (indexOfFocusedImage == 0);
			ImageFocus.overlay.querySelector(".slideshow-button.next").disabled = (indexOfFocusedImage == images.length - 1);

			//  Set the image number.
			ImageFocus.overlay.querySelector(".image-number").textContent = (indexOfFocusedImage + 1);

			//  Replace the hash.
			if (!location.hash.startsWith("#if_slide_"))
				ImageFocus.savedHash = location.hash;
			relocate("#if_slide_" + (indexOfFocusedImage + 1));

			//	Also preload the next and previous images.
			if (indexOfFocusedImage > 0)
				ImageFocus.preloadImage(images[indexOfFocusedImage - 1]);
			if (indexOfFocusedImage < images.length - 1)
				ImageFocus.preloadImage(images[indexOfFocusedImage + 1]);
		}

		//	Save reference to newly focused image.
		ImageFocus.currentlyFocusedImage = imageToFocus;

		//	Scroll to focused image, if need be.
		if (scrollToImage)
			revealElement(ImageFocus.currentlyFocusedImage);

		//  Create the focused version of the image.
		ImageFocus.imageInFocus = newElement("IMG", {
			src: ImageFocus.focusedImgSrcForImage(imageToFocus),
			loading: "eager",
			decoding: "sync",
			style: ("filter: " + imageToFocus.style.filter + " " + ImageFocus.dropShadowFilterForImages)
		});

		//  Add the image to the overlay.
		ImageFocus.overlay.insertBefore(ImageFocus.imageInFocus, ImageFocus.overlay.querySelector(".loading-spinner"));

		//  Set image to default size and position.
		ImageFocus.resetFocusedImagePosition(true);

		//  If image is bigger than viewport, it’s draggable.
		ImageFocus.imageInFocus.addEventListener("mousedown", ImageFocus.imageMouseDown);

		//  If image is bigger than viewport, double-click resets size/position.
		ImageFocus.imageInFocus.addEventListener("dblclick", ImageFocus.doubleClick);

		/*  If this image is part of the main gallery, then mark the overlay as 
			being in slide show mode (to show buttons/count). Otherwise, the
			overlay should be in single-image mode.
		 */
		ImageFocus.overlay.classList.toggle("slideshow", imageToFocus.classList.contains("gallery-image"));

		//  Set the caption.
		ImageFocus.setImageFocusCaption();

		//	Fire event.
		GW.notificationCenter.fireEvent("ImageFocus.imageDidFocus", { image: imageToFocus });
	},

	resetFocusedImagePosition: (updateOnLoad = false) => {
		GWLog("ImageFocus.resetFocusedImagePosition", "image-focus.js", 2);

		if (ImageFocus.imageInFocus == null)
			return;

		//  Make sure that initially, the image fits into the viewport.
		let imageWidth, imageHeight;
		if ((URLFromString(ImageFocus.imageInFocus.src)).pathname.endsWith(".svg")) {
			//	Special handling for SVGs, which have no intrinsic size.
			if (ImageFocus.imageInFocus.dataset.aspectRatio > "") {
				ImageFocus.imageInFocus.style.aspectRatio = ImageFocus.imageInFocus.dataset.aspectRatio;

				let parts = ImageFocus.imageInFocus.dataset.aspectRatio.match(/([0-9]+) \/ ([0-9]+)/);
				let aspectRatio = parseInt(parts[1]) / parseInt(parts[2]);
				imageWidth = window.innerHeight * aspectRatio;
				imageHeight = window.innerHeight;
			} else {
				imageWidth = imageHeight = Math.min(window.innerWidth, window.innerHeight);
			}
		} else {
			//	Non-SVGs have intrinsic size.
			if (updateOnLoad) {
				//	Reset on load.
				ImageFocus.imageInFocus.classList.add("loading");
				ImageFocus.imageInFocus.addEventListener("load", (event) => {
					ImageFocus.imageInFocus.classList.remove("loading");
					ImageFocus.resetFocusedImagePosition();
				}, { once: true });
			}

			//	If the image hasn’t loaded yet, these will both be 0.
			imageWidth = ImageFocus.imageInFocus.naturalWidth;
			imageHeight = ImageFocus.imageInFocus.naturalHeight;

			/*	If we don’t have the image’s actual dimensions yet (because we
				are still waiting for it to load), we nevertheless try to size
				the image element according to what information we have about
				how big the image will be when it loads.
			 */
			if (imageWidth * imageHeight == 0) {
				let expectedDimensions = ImageFocus.expectedDimensionsForImage(ImageFocus.currentlyFocusedImage);
				if (expectedDimensions) {
					imageWidth = expectedDimensions.width;
					imageHeight = expectedDimensions.height;
				}
			}
		}

		//	If we have no size info at all (yet), we do nothing.
		if (imageWidth * imageHeight == 0)
			return;

		//	Constrain dimensions proportionally.
		let constrainedWidth = Math.min(imageWidth, window.innerWidth * ImageFocus.shrinkRatio);
		let widthShrinkRatio = constrainedWidth / imageWidth;
		let constrainedHeight = Math.min(imageHeight, window.innerHeight * ImageFocus.shrinkRatio);
		let heightShrinkRatio = constrainedHeight / imageHeight;
		let shrinkRatio = Math.min(widthShrinkRatio, heightShrinkRatio);

		//	Set dimensions via CSS.
		ImageFocus.imageInFocus.style.width = Math.round(imageWidth * shrinkRatio) + "px";
		ImageFocus.imageInFocus.style.height = Math.round(imageHeight * shrinkRatio) + "px";

		//  Remove modifications to position.
		ImageFocus.imageInFocus.style.left = "";
		ImageFocus.imageInFocus.style.top = "";

		//  Set the cursor appropriately.
		ImageFocus.setFocusedImageCursor();
	},

	setFocusedImageCursor: () => {
		GWLog("ImageFocus.setFocusedImageCursor", "image-focus.js", 2);

		if (ImageFocus.imageInFocus == null)
			return;

		ImageFocus.imageInFocus.style.cursor = (   ImageFocus.imageInFocus.height >= window.innerHeight
												|| ImageFocus.imageInFocus.width >= window.innerWidth)
											   ? "move"
											   : "";
	},

	unfocusImage: () => {
		GWLog("ImageFocus.unfocusImage", "image-focus.js", 1);

		//  Remove image from overlay.
		if (ImageFocus.imageInFocus) {
			ImageFocus.imageInFocus.remove();
			ImageFocus.imageInFocus = null;
		}

		//	Update currently focused image in page.
		if (ImageFocus.currentlyFocusedImage) {
			//	Save reference to image-to-be-unfocused.
			let unfocusedImage = ImageFocus.currentlyFocusedImage;

			ImageFocus.currentlyFocusedImage.classList.remove("focused");
			ImageFocus.currentlyFocusedImage = null;

			//	Fire event.
			GW.notificationCenter.fireEvent("ImageFocus.imageDidUnfocus", { image: unfocusedImage });
		}
	},

	enterImageFocus: () => {
		GWLog("ImageFocus.enterImageFocus", "image-focus.js", 1);

		if (ImageFocus.overlay.classList.contains("engaged"))
			return;

		//	Show overlay.
		ImageFocus.overlay.classList.add("engaged");

		//  Add listener to zoom image with scroll wheel.
		window.addEventListener("wheel", ImageFocus.scrollEvent, { passive: false });

		//  Escape key unfocuses, spacebar resets.
		document.addEventListener("keyup", ImageFocus.keyUp);

		//  Prevent spacebar or arrow keys from scrolling page when image focused.
		requestAnimationFrame(() => {
			togglePageScrolling(false);
		});

		//  Moving mouse unhides image focus UI.
		if (GW.isMobile() == false)
			window.addEventListener("mousemove", ImageFocus.mouseMoved);

		//	Drag-end event; also, click to unfocus.
		window.addEventListener("mouseup", ImageFocus.mouseUp);

		//	Fire event.
		GW.notificationCenter.fireEvent("ImageFocus.imageOverlayDidAppear");
	},

	exitImageFocus: () => {
		GWLog("ImageFocus.exitImageFocus", "image-focus.js", 1);

		/*	If currently focused image is part of the main image gallery, 
			preserve state.
		 */
		if (   ImageFocus.currentlyFocusedImage
			&& ImageFocus.currentlyFocusedImage.classList.contains("gallery-image")) {
			//	Update classes.
			ImageFocus.currentlyFocusedImage.classList.remove("focused");

			if (ImageFocus.currentlyFocusedImage.classList.contains("gallery-image")) {
				ImageFocus.currentlyFocusedImage.classList.add("last-focused");

				//  Set accesskey of currently focused image, to re-focus it.
				ImageFocus.currentlyFocusedImage.accessKey = "l";
			}

			//  Reset the hash, if needed.
			if (location.hash.startsWith("#if_slide_")) {
				let previousURL = URLFromString(location.href);
				previousURL.hash = ImageFocus.savedHash ?? "";
				relocate(previousURL.href);

				ImageFocus.savedHash = null;
			}
		}

		//	Unfocus currently focused image.
		ImageFocus.unfocusImage();

		//  Remove event listeners.
		document.removeEventListener("keyup", ImageFocus.keyUp);
		window.removeEventListener("wheel", ImageFocus.scrollEvent);
		window.removeEventListener("mouseup", ImageFocus.mouseUp);
		if (GW.isMobile() == false)
			window.removeEventListener("mousemove", ImageFocus.mouseMoved);

		//  Hide overlay.
		ImageFocus.overlay.classList.remove("engaged");

		requestAnimationFrame(() => {
			//  Re-enable page scrolling.
			togglePageScrolling(true);
		});

		//	Fire event.
		GW.notificationCenter.fireEvent("ImageFocus.imageOverlayDidDisappear");
	},

	getIndexOfFocusedImage: () => {
		let images = document.querySelectorAll(ImageFocus.galleryImagesSelector);
		let indexOfFocusedImage = -1;
		for (i = 0; i < images.length; i++) {
			if (images[i].classList.contains("focused")) {
				indexOfFocusedImage = i;
				break;
			}
		}
		return indexOfFocusedImage;
	},

	focusNextImage: (next = true) => {
		GWLog("ImageFocus.focusNextImage", "image-focus.js", 1);

		//	Find next image to focus.
		let images = document.querySelectorAll(ImageFocus.galleryImagesSelector);
		let indexOfFocusedImage = ImageFocus.getIndexOfFocusedImage();

		//	This shouldn’t happen, but...
		if (next ? (++indexOfFocusedImage == images.length) : (--indexOfFocusedImage == -1))
			return;

		//	Focus new image.
		ImageFocus.focusImage(images[indexOfFocusedImage]);
	},

	setImageFocusCaption: () => {
		GWLog("ImageFocus.setImageFocusCaption", "image-focus.js", 2);

		//	Used in comparison below.
		function textContentOf(node) {
			return node.textContent.trim().replace(/\s+/g, " ");
		}

		//	For truncating very long URLs.
		function truncatedURLString(urlString) {
			let maxLength = 160;
			return urlString.length > maxLength
				   ? urlString.slice(0, maxLength) + "…"
				   : urlString;
		}

		/*	Get the figure caption, the ‘title’ attribute of the image, and the 
			‘alt’ attribute of the image. Clean each of typographic invisibles
			and educate quotes. Discard duplicate strings. Wrap all remaining 
			(unique) strings in <p> tags, and inject into caption container.
		 */
		let figcaption = ImageFocus.currentlyFocusedImage.closest("figure").querySelector("figcaption");
		ImageFocus.overlay.querySelector(".caption").replaceChildren(newDocument(`<div class="caption-text-wrapper">` 
		  + [ ...[
				(figcaption ? figcaption.cloneNode(true) : null),
				newElement("SPAN", null, { "innerHTML": ImageFocus.currentlyFocusedImage.getAttribute("title") }),
				newElement("SPAN", null, { "innerHTML": ImageFocus.currentlyFocusedImage.getAttribute("alt") }),
			].map(element => {
				if (element)
					Typography.processElement(element, Typography.replacementTypes.CLEAN|Typography.replacementTypes.QUOTES);

				if (element?.tagName == "FIGCAPTION")
					element.innerHTML = Array.from(element.children).map(p => p.innerHTML).join("<br>\n<br>\n");

				return element;
			}).filter((element, index, array) => (
					element != null
				 && isNodeEmpty_metadataAware(element) == false
				 && textContentOf(element) != GW.defaultImageAuxText
				 && array.findIndex(otherElement => (
				 		otherElement != null
					 && textContentOf(otherElement) == textContentOf(element))
					) == index)
			).map(element => 
				`<p>${(element.innerHTML.trim())}</p>`
			)].join("") 
		  + `</div>`
		  + `<p class="image-url" title="Click to copy image URL to clipboard">`
		  	  + (ImageFocus.imageInFocus.src.startsWith("data:")
		  	     ? ``
		  	     : (  `<code class="url">`
					+ truncatedURLString(ImageFocus.imageInFocus.src)
					+ `</code>`))
			  + `<span class="icon-container">`
				  + `<span class="icon normal">`
					  + GW.svg("copy-regular")
				  + `</span>`
				  + `<span class="icon copied">`
					  + GW.svg("circle-check-solid")
				  + `</span>`
			  + `</span>`
		  + `</p>`));

		//	Activate click-to-copy on image URL.
		let imageURLContainer = ImageFocus.overlay.querySelector(".caption .image-url");
		imageURLContainer.addActivateEvent((event) => {
			copyTextToClipboard(ImageFocus.currentlyFocusedImage.src);

			//	Update icon.
			imageURLContainer.classList.add("copied");

            //  Flash URL, for visual feedback of copy operation.
            imageURLContainer.classList.add("flash");
            setTimeout(() => { imageURLContainer.classList.remove("flash"); }, 150);
		});
		imageURLContainer.addEventListener("mouseleave", (event) => {
			//	Reset icon.
			imageURLContainer.classList.remove("copied");
		});
	},

	focusImageSpecifiedByURL: () => {
		GWLog("ImageFocus.focusImageSpecifiedByURL", "image-focus.js", 1);

		if (location.hash.startsWith("#if_slide_")) {
			doWhenPageLoaded(() => {
				let images = document.querySelectorAll(ImageFocus.galleryImagesSelector);
				let imageToFocus = (/#if_slide_([0-9]+)/.exec(location.hash)||{})[1];
				if (   imageToFocus > 0
					&& imageToFocus <= images.length) {
					ImageFocus.focusImage(images[imageToFocus - 1]);
				}
			});
		}
	},

	/************************************/
	/* Image gallery UI showing / hiding.
	 ************************************/

	hideImageFocusUI: () => {
		GWLog("ImageFocus.hideImageFocusUI", "image-focus.js", 3);

		ImageFocus.overlay.querySelectorAll(ImageFocus.imageFocusUIElementsSelector).forEach(element => {
			element.classList.toggle("hidden", true);
		});
	},

	hideUITimerExpired: () => {
		GWLog("ImageFocus.hideUITimerExpired", "image-focus.js", 3);

		let timeSinceLastMouseMove = (new Date()) - ImageFocus.mouseLastMovedAt;
		if (timeSinceLastMouseMove < ImageFocus.hideUITimerDuration) {
			ImageFocus.hideUITimer = setTimeout(ImageFocus.hideUITimerExpired, (ImageFocus.hideUITimerDuration - timeSinceLastMouseMove));
		} else {
			ImageFocus.hideImageFocusUI();
			ImageFocus.cancelImageFocusHideUITimer();
		}
	},

	unhideImageFocusUI: () => {
		GWLog("ImageFocus.unhideImageFocusUI", "image-focus.js", 3);

		ImageFocus.overlay.querySelectorAll(ImageFocus.imageFocusUIElementsSelector).forEach(element => {
			element.classList.toggle("hidden", false);
		});

		ImageFocus.hideUITimer = setTimeout(ImageFocus.hideUITimerExpired, ImageFocus.hideUITimerDuration);
	},

	cancelImageFocusHideUITimer: () => {
		GWLog("ImageFocus.cancelImageFocusHideUITimer", "image-focus.js", 3);

		clearTimeout(ImageFocus.hideUITimer);
		ImageFocus.hideUITimer = null;
	},

	/*********/
	/* Events.
	 *********/

	//  Event listener for clicking on images to focus them.
	imageClickedToFocus: (event) => {
		GWLog("ImageFocus.imageClickedToFocus", "image-focus.js", 2);

		//	Focus the clicked image, but don’t scroll to it.
		ImageFocus.focusImage(event.target, false);
	},

	scrollEvent: (event) => {
		GWLog("ImageFocus.scrollEvent", "image-focus.js", 3);

		event.preventDefault();

		let image = ImageFocus.imageInFocus;

		//  Remove the filter.
		image.savedFilter = image.style.filter;
		image.style.filter = "none";

		//  Get bounding box of the image within the viewport.
		let imageBoundingBox = image.getBoundingClientRect();

		//  Calculate resize factor.
		let factor = ((image.height > 10 && image.width > 10) || event.deltaY < 0)
					 ? 1 + Math.sqrt(Math.abs(event.deltaY))/100.0
					 : 1;

		//  Resize.
		image.style.width = (event.deltaY < 0 ?
							(image.clientWidth * factor) :
							(image.clientWidth / factor))
							+ "px";
		image.style.height = "auto";

		//  Designate zoom origin.
		let zoomOrigin;

		//  Zoom from cursor if we’re zoomed in to where image exceeds screen, AND
		//  the cursor is over the image.
		let imageSizeExceedsWindowBounds = (   image.getBoundingClientRect().width > window.innerWidth
											|| image.getBoundingClientRect().height > window.innerHeight);
		let zoomingFromCursor =    imageSizeExceedsWindowBounds
								&& (   imageBoundingBox.left <= event.clientX
									&& event.clientX <= imageBoundingBox.right
									&& imageBoundingBox.top <= event.clientY
									&& event.clientY <= imageBoundingBox.bottom);

		//  Otherwise, if we’re zooming OUT, zoom from window center; if we’re
		//  zooming IN, zoom from image center.
		let zoomingFromWindowCenter = event.deltaY > 0;
		if (zoomingFromCursor)
			zoomOrigin = { x: event.clientX,
						   y: event.clientY };
		else if (zoomingFromWindowCenter)
			zoomOrigin = { x: window.innerWidth / 2,
						   y: window.innerHeight / 2 };
		else
			zoomOrigin = { x: imageBoundingBox.x + imageBoundingBox.width / 2,
						   y: imageBoundingBox.y + imageBoundingBox.height / 2 };

		//  Calculate offset from zoom origin.
		let offsetOfImageFromZoomOrigin = {
			x: imageBoundingBox.x - zoomOrigin.x,
			y: imageBoundingBox.y - zoomOrigin.y
		}

		//  Calculate delta from centered zoom.
		let deltaFromCenteredZoom = {
			x: image.getBoundingClientRect().x - (zoomOrigin.x + (event.deltaY < 0 ? offsetOfImageFromZoomOrigin.x * factor : offsetOfImageFromZoomOrigin.x / factor)),
			y: image.getBoundingClientRect().y - (zoomOrigin.y + (event.deltaY < 0 ? offsetOfImageFromZoomOrigin.y * factor : offsetOfImageFromZoomOrigin.y / factor))
		}

		//  Adjust image position appropriately.
		image.style.left = parseInt(getComputedStyle(image).left) - deltaFromCenteredZoom.x + "px";
		image.style.top = parseInt(getComputedStyle(image).top) - deltaFromCenteredZoom.y + "px";

		//  Gradually re-center image, if it’s smaller than the window.
		if (!imageSizeExceedsWindowBounds) {
			let imageCenter = { x: image.getBoundingClientRect().x + image.getBoundingClientRect().width / 2,
								y: image.getBoundingClientRect().y + image.getBoundingClientRect().height / 2 }
			let windowCenter = { x: window.innerWidth / 2,
								 y: window.innerHeight / 2 }
			let imageOffsetFromCenter = { x: windowCenter.x - imageCenter.x,
										  y: windowCenter.y - imageCenter.y }

			//  Divide the offset by 10 because we’re nudging the image toward center,
			//  not jumping it there.
			image.style.left = parseInt(getComputedStyle(image).left) + imageOffsetFromCenter.x / 10 + "px";
			image.style.top = parseInt(getComputedStyle(image).top) + imageOffsetFromCenter.y / 10 + "px";
		}

		//  Put the filter back.
		image.style.filter = image.savedFilter;

		//  Set the cursor appropriately.
		ImageFocus.setFocusedImageCursor();
	},

	mouseUp: (event) => {
		GWLog("ImageFocus.mouseUp", "image-focus.js", 2);

		//	Different handling for drag-end events than clicks.
		let imageWasBeingDragged = (window.onmousemove != null);

		//	Do this regardless of where the mouse-up is.
		if (   imageWasBeingDragged
			&& (   ImageFocus.imageInFocus.height >= window.innerHeight
				|| ImageFocus.imageInFocus.width >= window.innerWidth)) {
			window.onmousemove = "";

			//  Put the filter back.
			ImageFocus.imageInFocus.style.filter = ImageFocus.imageInFocus.savedFilter;
		}

		//	On mobile, tap when UI is hidden unhides UI.
		if (   GW.isMobile() 
			&& imageWasBeingDragged == false) {
			if (ImageFocus.hideUITimer == null) {
				//	If the UI was hidden, tap unhides it.
				ImageFocus.unhideImageFocusUI();

				/*	If caption is locked-unhidden, unlock it now (so that it 
					will be hidden along with the rest of the UI once the 
					timer expires).
				 */
				ImageFocus.overlay.querySelector(".caption").classList.remove("locked");

				//	A tap in this case does nothing else.
				return;
			} else if (event.target.closest(".caption") != null) {
				//	Lock-unhide caption, if tap is on it.
				ImageFocus.overlay.querySelector(".caption").classList.add("locked");
			}
		}

		//	Do nothing more if click is on a UI element.
		if (event.target.closest(ImageFocus.imageFocusUIElementsSelector))
			return;

		//  We only want to do anything on left-clicks.
		if (event.button != 0)
			return;

		//	Exit image focus, if image is not zoomed in.
		if (   (   ImageFocus.imageInFocus.height < window.innerHeight
				&& ImageFocus.imageInFocus.width < window.innerWidth)
			|| (   imageWasBeingDragged == false
				&& event.target != ImageFocus.imageInFocus))
			ImageFocus.exitImageFocus();
	},

	imageMouseDown: (event) => {
		GWLog("ImageFocus.imageMouseDown", "image-focus.js", 2);

		//  We only want to do anything on left-clicks.
		if (event.button != 0)
			return;

		//	Prevent browser/system drag-and-drop initiate.
		event.preventDefault();

		if (   ImageFocus.imageInFocus.height >= window.innerHeight
			|| ImageFocus.imageInFocus.width >= window.innerWidth) {
			let mouseCoordX = event.clientX;
			let mouseCoordY = event.clientY;

			let imageCoordX = parseInt(getComputedStyle(ImageFocus.imageInFocus).left);
			let imageCoordY = parseInt(getComputedStyle(ImageFocus.imageInFocus).top);

			//  Save the filter.
			ImageFocus.imageInFocus.savedFilter = ImageFocus.imageInFocus.style.filter;

			window.onmousemove = (event) => {
				//  Remove the filter.
				ImageFocus.imageInFocus.style.filter = "none";
				ImageFocus.imageInFocus.style.left = imageCoordX + event.clientX - mouseCoordX + "px";
				ImageFocus.imageInFocus.style.top = imageCoordY + event.clientY - mouseCoordY + "px";
			};
			return false;
		}
	},

	doubleClick: (event) => {
		GWLog("ImageFocus.doubleClick", "image-focus.js", 2);

		if (   ImageFocus.imageInFocus.height >= window.innerHeight
			|| ImageFocus.imageInFocus.width >= window.innerWidth)
			ImageFocus.resetFocusedImagePosition();
	},

	keyUp: (event) => {
		GWLog("ImageFocus.keyUp", "image-focus.js", 3);

		let allowedKeys = [ " ", "Spacebar", "Escape", "Esc", "ArrowUp", "ArrowDown", "ArrowLeft", "ArrowRight", "Up", "Down", "Left", "Right" ];
		if (   !allowedKeys.includes(event.key)
			|| getComputedStyle(ImageFocus.overlay).display == "none")
			return;

		event.preventDefault();

		switch (event.key) {
		case "Escape":
		case "Esc":
			ImageFocus.exitImageFocus();
			break;
		case " ":
		case "Spacebar":
			ImageFocus.resetFocusedImagePosition();
			break;
		case "ArrowDown":
		case "Down":
		case "ArrowRight":
		case "Right":
			if (   ImageFocus.currentlyFocusedImage
				&& ImageFocus.currentlyFocusedImage.classList.contains("gallery-image"))
				ImageFocus.focusNextImage(true);
			break;
		case "ArrowUp":
		case "Up":
		case "ArrowLeft":
		case "Left":
			if (   ImageFocus.currentlyFocusedImage
				&& ImageFocus.currentlyFocusedImage.classList.contains("gallery-image"))
				ImageFocus.focusNextImage(false);
			break;
		}
	},

	mouseMoved: (event) => {
		GWLog("ImageFocus.mouseMoved", "image-focus.js", 3);

		let currentDateTime = new Date();

		if ([ ImageFocus.imageInFocus, 
			  ImageFocus.overlay, 
			  document.documentElement 
			 ].includes(event.target)) {
			if (ImageFocus.hideUITimer == null)
				ImageFocus.unhideImageFocusUI();

			ImageFocus.mouseLastMovedAt = currentDateTime;
		} else {
			ImageFocus.cancelImageFocusHideUITimer();
		}
	}
};

GW.notificationCenter.fireEvent("ImageFocus.didLoad");

ImageFocus.setup();

//	If the URL specifies an image, focus it after the page has loaded.
ImageFocus.focusImageSpecifiedByURL();