From cc18a90a860f8483e8cfb6fb5342c9a27592e4b1 Mon Sep 17 00:00:00 2001
From: Cory LaViska <cory@abeautifulsite.net>
Date: Thu, 12 Oct 2023 12:11:20 -0400
Subject: [PATCH] backport PR 1600

---
 docs/pages/resources/changelog.md             |  1 +
 package.json                                  | 16 ++---------
 src/components/menu-item/menu-item.styles.ts  | 24 ++++++++++++++++
 .../menu-item/submenu-controller.ts           | 28 +++++++++++++++++++
 4 files changed, 56 insertions(+), 13 deletions(-)

diff --git a/docs/pages/resources/changelog.md b/docs/pages/resources/changelog.md
index 0b312467a..2cd3ba672 100644
--- a/docs/pages/resources/changelog.md
+++ b/docs/pages/resources/changelog.md
@@ -16,6 +16,7 @@ New versions of Web Awesome are released as-needed and generally occur when a cr
 
 - Changed the `sl` prefix to `wa` for Web Awesome, including tags, events, etc.
 - Changed `primary` variants to `brand` in all components
+- Improved submenu selection by implementing the [safe triangle](https://www.smashingmagazine.com/2023/08/better-context-menus-safe-triangles/) method [#1550]
 - Removed `default` from `<wa-button>` and made `neutral` the new default
 - Removed the `circle` modifier from `<wa-button>` because button's no longer have a set height
 
diff --git a/package.json b/package.json
index 3c45dd21f..9339be4eb 100644
--- a/package.json
+++ b/package.json
@@ -25,15 +25,8 @@
     "./dist/react/*": "./dist/react/*",
     "./dist/translations/*": "./dist/translations/*"
   },
-  "files": [
-    "dist",
-    "cdn"
-  ],
-  "keywords": [
-    "web components",
-    "custom elements",
-    "components"
-  ],
+  "files": ["dist", "cdn"],
+  "keywords": ["web components", "custom elements", "components"],
   "repository": {
     "type": "git",
     "url": "git+https://github.com/shoelace-style/shoelace.git"
@@ -136,9 +129,6 @@
     "user-agent-data-types": "^0.3.0"
   },
   "lint-staged": {
-    "*.{ts,js}": [
-      "eslint --max-warnings 0 --cache --fix",
-      "prettier --write"
-    ]
+    "*.{ts,js}": ["eslint --max-warnings 0 --cache --fix", "prettier --write"]
   }
 }
diff --git a/src/components/menu-item/menu-item.styles.ts b/src/components/menu-item/menu-item.styles.ts
index 2de777921..18bb7af6c 100644
--- a/src/components/menu-item/menu-item.styles.ts
+++ b/src/components/menu-item/menu-item.styles.ts
@@ -7,6 +7,14 @@ export default css`
   :host {
     --submenu-offset: -2px;
 
+    /* Private */
+    --safe-triangle-cursor-x: 0;
+    --safe-triangle-cursor-y: 0;
+    --safe-triangle-submenu-start-x: 0;
+    --safe-triangle-submenu-start-y: 0;
+    --safe-triangle-submenu-end-x: 0;
+    --safe-triangle-submenu-end-y: 0;
+
     display: block;
   }
 
@@ -60,6 +68,22 @@ export default css`
     margin-inline-start: var(--wa-space-xs);
   }
 
+  /* Safe triangle */
+  .menu-item--submenu-expanded::after {
+    content: '';
+    position: fixed;
+    z-index: calc(var(--wa-z-index-dropdown) - 1);
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    clip-path: polygon(
+      var(--safe-triangle-cursor-x) var(--safe-triangle-cursor-y),
+      var(--safe-triangle-submenu-start-x) var(--safe-triangle-submenu-start-y),
+      var(--safe-triangle-submenu-end-x) var(--safe-triangle-submenu-end-y)
+    );
+  }
+
   :host(:focus-visible) {
     outline: none;
   }
diff --git a/src/components/menu-item/submenu-controller.ts b/src/components/menu-item/submenu-controller.ts
index 535c76459..58ceb74bd 100644
--- a/src/components/menu-item/submenu-controller.ts
+++ b/src/components/menu-item/submenu-controller.ts
@@ -49,6 +49,7 @@ export class SubmenuController implements ReactiveController {
 
   private addListeners() {
     if (!this.isConnected) {
+      this.host.addEventListener('mousemove', this.handleMouseMove);
       this.host.addEventListener('mouseover', this.handleMouseOver);
       this.host.addEventListener('keydown', this.handleKeyDown);
       this.host.addEventListener('click', this.handleClick);
@@ -61,6 +62,7 @@ export class SubmenuController implements ReactiveController {
     if (!this.isPopupConnected) {
       if (this.popupRef.value) {
         this.popupRef.value.addEventListener('mouseover', this.handlePopupMouseover);
+        this.popupRef.value.addEventListener('wa-reposition', this.handlePopupReposition);
         this.isPopupConnected = true;
       }
     }
@@ -68,6 +70,7 @@ export class SubmenuController implements ReactiveController {
 
   private removeListeners() {
     if (this.isConnected) {
+      this.host.removeEventListener('mousemove', this.handleMouseMove);
       this.host.removeEventListener('mouseover', this.handleMouseOver);
       this.host.removeEventListener('keydown', this.handleKeyDown);
       this.host.removeEventListener('click', this.handleClick);
@@ -77,11 +80,18 @@ export class SubmenuController implements ReactiveController {
     if (this.isPopupConnected) {
       if (this.popupRef.value) {
         this.popupRef.value.removeEventListener('mouseover', this.handlePopupMouseover);
+        this.popupRef.value.removeEventListener('wa-reposition', this.handlePopupReposition);
         this.isPopupConnected = false;
       }
     }
   }
 
+  // Set the safe triangle cursor position
+  private handleMouseMove = (event: MouseEvent) => {
+    this.host.style.setProperty('--safe-triangle-cursor-x', `${event.clientX}px`);
+    this.host.style.setProperty('--safe-triangle-cursor-y', `${event.clientY}px`);
+  };
+
   private handleMouseOver = () => {
     if (this.hasSlotController.test('submenu')) {
       this.enableSubmenu();
@@ -188,6 +198,24 @@ export class SubmenuController implements ReactiveController {
     event.stopPropagation();
   };
 
+  // Set the safe triangle values for the submenu when the position changes
+  private handlePopupReposition = () => {
+    const submenuSlot: HTMLSlotElement | null = this.host.renderRoot.querySelector("slot[name='submenu']");
+    const menu = submenuSlot?.assignedElements({ flatten: true }).filter(el => el.localName === 'wa-menu')[0];
+    const isRtl = this.localize.dir() === 'rtl';
+
+    if (!menu) {
+      return;
+    }
+
+    const { left, top, width, height } = menu.getBoundingClientRect();
+
+    this.host.style.setProperty('--safe-triangle-submenu-start-x', `${isRtl ? left + width : left}px`);
+    this.host.style.setProperty('--safe-triangle-submenu-start-y', `${top}px`);
+    this.host.style.setProperty('--safe-triangle-submenu-end-x', `${isRtl ? left + width : left}px`);
+    this.host.style.setProperty('--safe-triangle-submenu-end-y', `${top + height}px`);
+  };
+
   private setSubmenuState(state: boolean) {
     if (this.popupRef.value) {
       if (this.popupRef.value.active !== state) {