From b53ee54e4f1172a0d13ef0808b7236c176bf8d1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=8B=E3=81=A3=E3=81=93=E3=81=8B=E3=82=8A?=
 <67428053+kakkokari-gtyih@users.noreply.github.com>
Date: Sun, 18 Aug 2024 14:18:46 +0900
Subject: [PATCH] =?UTF-8?q?fix(frontend):=20focustrap=E3=81=8Czindex?=
 =?UTF-8?q?=E3=82=92=E8=80=83=E6=85=AE=E3=81=99=E3=82=8B=E3=82=88=E3=81=86?=
 =?UTF-8?q?=E3=81=AB=20(#14431)?=
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---
 packages/frontend/src/scripts/focus-trap.ts | 64 +++++++++++++++++++--
 1 file changed, 60 insertions(+), 4 deletions(-)

diff --git a/packages/frontend/src/scripts/focus-trap.ts b/packages/frontend/src/scripts/focus-trap.ts
index a5df36f520..fb7caea830 100644
--- a/packages/frontend/src/scripts/focus-trap.ts
+++ b/packages/frontend/src/scripts/focus-trap.ts
@@ -16,21 +16,57 @@ function containsFocusTrappedElements(el: HTMLElement): boolean {
 	});
 }
 
+function getZIndex(el: HTMLElement): number {
+	const zIndex = parseInt(window.getComputedStyle(el).zIndex || '0', 10);
+	if (isNaN(zIndex)) {
+		return 0;
+	}
+	return zIndex;
+}
+
+function getHighestZIndexElement(): { el: HTMLElement; zIndex: number; } | null {
+	let highestZIndexElement: HTMLElement | null = null;
+	let highestZIndex = -Infinity;
+
+	focusTrapElements.forEach((el) => {
+		const zIndex = getZIndex(el);
+		if (zIndex > highestZIndex) {
+			highestZIndex = zIndex;
+			highestZIndexElement = el;
+		}
+	});
+
+	return highestZIndexElement == null ? null : {
+		el: highestZIndexElement,
+		zIndex: highestZIndex,
+	};
+}
+
 function releaseFocusTrap(el: HTMLElement): void {
 	focusTrapElements.delete(el);
 	if (el.inert === true) {
 		el.inert = false;
 	}
+
+	const highestZIndexElement = getHighestZIndexElement();
+
 	if (el.parentElement != null && el !== document.body) {
 		el.parentElement.childNodes.forEach((siblingNode) => {
 			const siblingEl = getHTMLElementOrNull(siblingNode);
 			if (!siblingEl) return;
-			if (siblingEl !== el && (focusTrapElements.has(siblingEl) || containsFocusTrappedElements(siblingEl) || focusTrapElements.size === 0)) {
+			if (
+				siblingEl !== el &&
+				(
+					highestZIndexElement == null ||
+					siblingEl === highestZIndexElement.el ||
+					siblingEl.contains(highestZIndexElement.el)
+				)
+			) {
 				siblingEl.inert = false;
 			} else if (
-				focusTrapElements.size > 0 &&
-				!containsFocusTrappedElements(siblingEl) &&
-				!focusTrapElements.has(siblingEl) &&
+				highestZIndexElement != null &&
+				siblingEl !== highestZIndexElement.el &&
+				!siblingEl.contains(highestZIndexElement.el) &&
 				!ignoreElements.includes(siblingEl.tagName.toLowerCase())
 			) {
 				siblingEl.inert = true;
@@ -45,9 +81,29 @@ function releaseFocusTrap(el: HTMLElement): void {
 export function focusTrap(el: HTMLElement, hasInteractionWithOtherFocusTrappedEls: boolean, parent: true): void;
 export function focusTrap(el: HTMLElement, hasInteractionWithOtherFocusTrappedEls?: boolean, parent?: false): { release: () => void; };
 export function focusTrap(el: HTMLElement, hasInteractionWithOtherFocusTrappedEls = false, parent = false): { release: () => void; } | void {
+	const highestZIndexElement = getHighestZIndexElement();
+
+	const highestZIndex = highestZIndexElement == null ? -Infinity : highestZIndexElement.zIndex;
+	const zIndex = getZIndex(el);
+
+	// If the element has a lower z-index than the highest z-index element, focus trap the highest z-index element instead
+	// Focus trapping for this element will be done in the release function
+	if (!parent && zIndex < highestZIndex) {
+		focusTrapElements.add(el);
+		if (highestZIndexElement) {
+			focusTrap(highestZIndexElement.el, hasInteractionWithOtherFocusTrappedEls);
+		}
+		return {
+			release: () => {
+				releaseFocusTrap(el);
+			},
+		};
+	}
+
 	if (el.inert === true) {
 		el.inert = false;
 	}
+
 	if (el.parentElement != null && el !== document.body) {
 		el.parentElement.childNodes.forEach((siblingNode) => {
 			const siblingEl = getHTMLElementOrNull(siblingNode);