From b024fbf1a172d8ebe0c05531f689395f97f3ea7b Mon Sep 17 00:00:00 2001
From: thattonBL <79150422+thattonBL@users.noreply.github.com>
Date: Wed, 23 Oct 2024 14:34:24 +0100
Subject: [PATCH] Restrict tab focus to within modal dialogues when open (fixes
 #1070 and #1072) (#1163)

* Issues #1070 and #1072 Restrict tab focus to within modal dialogue elements when model-dialogue is open

- Add key listener override on Dialogue.ts which is the base class for most Dialogues
- Added code to do the same thing for the React Dowload Dialogue

* Amendments to Issues #1070 and #1072 Restrict tab focus to within modal dialogue elements when model-dialogue is open

- Changed the way in which the DownloadDialogue.tsx establishes the first element to give focus to on load
- Extracted the focusable elements logic to use for the above
- Removed added whitespace from Dialogue.ts

---------

Co-authored-by: thatton <thomasrichardhatton@googlemail.com>
---
 .../DownloadDialogue.tsx                      | 54 +++++++++++++++++--
 .../iiif/modules/uv-shared-module/Dialogue.ts | 33 +++++++++++-
 2 files changed, 82 insertions(+), 5 deletions(-)

diff --git a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/DownloadDialogue.tsx b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/DownloadDialogue.tsx
index db0cdd900..60a443d85 100644
--- a/src/content-handlers/iiif/extensions/uv-openseadragon-extension/DownloadDialogue.tsx
+++ b/src/content-handlers/iiif/extensions/uv-openseadragon-extension/DownloadDialogue.tsx
@@ -78,7 +78,6 @@ const DownloadDialogue = ({
   triggerButton: HTMLElement;
 }) => {
   const ref = useRef<HTMLDivElement>(null);
-
   const [position, setPosition] = useState({ top: "0px", left: "0px" });
   const [arrowPosition, setArrowPosition] = useState("0px 0px");
   const [selectedPage, setSelectedPage] = useState<"left" | "right">("left");
@@ -109,12 +108,59 @@ const DownloadDialogue = ({
 
       setPosition({ top: `${top}px`, left: `${left}px` });
       setArrowPosition(`${arrowLeft}px 0px`);
+
+      // Focus on the first element when opened
+      const focusableElements = getFocusableElements();
+      if (focusableElements && focusableElements.length > 0) {
+        focusableElements[0]?.focus();
+      }
     }
   }, [open]);
 
-  if (!open) {
-    return null;
-  }
+  // Method to get focusable elements inside the component
+  const getFocusableElements = (): NodeListOf<HTMLElement> | null => {
+    return ref.current?.querySelectorAll(
+      'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
+    ) as NodeListOf<HTMLElement>;
+  };
+
+
+  // Focus trapping logic
+  const handleTabKey = (e: KeyboardEvent) => {
+    if (e.key === "Tab") {
+      const focusableElements = getFocusableElements();
+      if (!focusableElements) return;
+
+      const firstFocusableElement = focusableElements[0] as HTMLElement;
+      const lastFocusableElement = focusableElements[focusableElements.length - 1] as HTMLElement;
+
+      if (e.shiftKey) {
+        // If Shift + Tab is pressed and the focus is on the first element, go to the last
+        if (document.activeElement === firstFocusableElement) {
+          e.preventDefault();
+          lastFocusableElement.focus();
+        }
+      } else {
+        // If Tab is pressed and the focus is on the last element, go to the first
+        if (document.activeElement === lastFocusableElement) {
+          e.preventDefault();
+          firstFocusableElement.focus();
+        }
+      }
+    }
+  };
+
+  useEffect(() => {
+    if (open) {
+      document.addEventListener("keydown", handleTabKey);
+    }
+
+    return () => {
+      document.removeEventListener("keydown", handleTabKey);
+    };
+  }, [open]);
+
+  if (!open) return null;
 
   function getCanvasDimensions(canvas: Canvas): Size | null {
     // externalResource may not have loaded yet
diff --git a/src/content-handlers/iiif/modules/uv-shared-module/Dialogue.ts b/src/content-handlers/iiif/modules/uv-shared-module/Dialogue.ts
index cedddb02d..0f067f3d2 100644
--- a/src/content-handlers/iiif/modules/uv-shared-module/Dialogue.ts
+++ b/src/content-handlers/iiif/modules/uv-shared-module/Dialogue.ts
@@ -28,7 +28,6 @@ export class Dialogue<
 
   create(): void {
     this.setConfig("dialogue");
-
     super.create();
 
     // events.
@@ -168,6 +167,9 @@ export class Dialogue<
       }
     }, 1);
 
+    // Add keydown event listener to trap focus within the dialog
+    this.$element.on("keydown", (e: JQuery.Event) => this.handleKeydown(e));
+
     this.extensionHost.publish(IIIFEvents.SHOW_OVERLAY);
 
     if (this.isUnopened) {
@@ -186,6 +188,9 @@ export class Dialogue<
     this.$element.hide();
     this.isActive = false;
 
+    // Remove the keydown event listener
+    this.$element.off("keydown");
+
     this.extensionHost.publish(this.closeCommand);
     this.extensionHost.publish(IIIFEvents.HIDE_OVERLAY);
   }
@@ -198,4 +203,30 @@ export class Dialogue<
       left: Math.floor(this.extension.width() / 2 - this.$element.width() / 2),
     });
   }
+
+  private handleKeydown(event: JQuery.Event): void {
+    if (event.key === "Tab") {
+        const focusableSelectors =
+            'a[href], button, textarea, input[type="text"], input[type="radio"], input[type="checkbox"], select, [tabindex="0"]';
+        const focusableElements = this.$element.find(focusableSelectors).filter(':visible');
+
+        const firstElement = focusableElements.first()[0];
+        const lastElement = focusableElements.last()[0];
+        const activeElement = document.activeElement;
+
+        if (event.shiftKey) {
+            // Shift + Tab (backwards)
+            if (activeElement === firstElement) {
+                event.preventDefault();
+                lastElement.focus();
+            }
+        } else {
+            // Tab (forwards)
+            if (activeElement === lastElement) {
+                event.preventDefault();
+                firstElement.focus();
+            }
+        }
+    }
+  }
 }