From 10445396dd50eb21e93625eaccd1658b2e2b186e Mon Sep 17 00:00:00 2001
From: Benny Powers <web@bennypowers.com>
Date: Mon, 31 Mar 2025 17:22:10 +0300
Subject: [PATCH 1/3] fix(core): activate scroll spy link on connect

---
 .../controllers/scroll-spy-controller.ts      | 23 ++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/core/pfe-core/controllers/scroll-spy-controller.ts b/core/pfe-core/controllers/scroll-spy-controller.ts
index 89af9d2481..efd0ad4356 100644
--- a/core/pfe-core/controllers/scroll-spy-controller.ts
+++ b/core/pfe-core/controllers/scroll-spy-controller.ts
@@ -43,6 +43,7 @@ export class ScrollSpyController implements ReactiveController {
   #root: ScrollSpyControllerOptions['root'];
   #rootMargin?: string;
   #threshold: number | number[];
+  #intersectingElements: Element[] = [];
 
   #getRootNode: () => Node;
   #getHash: (el: Element) => string | null;
@@ -100,7 +101,9 @@ export class ScrollSpyController implements ReactiveController {
     this.#initIo();
   }
 
-  #initIo() {
+  #initializing = true;
+
+  async #initIo() {
     const rootNode = this.#getRootNode();
     if (rootNode instanceof Document || rootNode instanceof ShadowRoot) {
       const { rootMargin, threshold, root } = this;
@@ -151,6 +154,24 @@ export class ScrollSpyController implements ReactiveController {
       this.#setActive(last ?? this.#linkChildren.at(0));
     }
     this.#intersected = true;
+    this.#intersectingElements =
+      entries
+          .filter(x => x.isIntersecting)
+          .map(x => x.target);
+    if (this.#initializing) {
+      const ints = entries?.filter(x => x.isIntersecting) ?? [];
+      if (this.#intersectingElements) {
+        const [{ target = null } = {}] = ints;
+        const { id } = target ?? {};
+        if (id) {
+          const link = this.#linkChildren.find(link => this.#getHash(link) === `#${id}`);
+          if (link) {
+            this.#setActive(link);
+          }
+        }
+      }
+      this.#initializing = false;
+    }
   }
 
   /**

From 3f64067ebf8edb8a9110819d4f471bdbe6bfb5df Mon Sep 17 00:00:00 2001
From: Benny Powers <web@bennypowers.com>
Date: Mon, 31 Mar 2025 17:50:24 +0300
Subject: [PATCH 2/3] feat(core): scroll-spy-controller onIntersection

---
 core/pfe-core/controllers/scroll-spy-controller.ts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/core/pfe-core/controllers/scroll-spy-controller.ts b/core/pfe-core/controllers/scroll-spy-controller.ts
index efd0ad4356..a5473ae24b 100644
--- a/core/pfe-core/controllers/scroll-spy-controller.ts
+++ b/core/pfe-core/controllers/scroll-spy-controller.ts
@@ -23,6 +23,10 @@ export interface ScrollSpyControllerOptions extends IntersectionObserverInit {
    * @default el => el.getAttribute('href');
    */
   getHash?: (el: Element) => string | null;
+  /**
+   * Optional callback for when an intersection occurs
+   */
+  onIntersection?(): void;
 }
 
 export class ScrollSpyController implements ReactiveController {
@@ -47,6 +51,7 @@ export class ScrollSpyController implements ReactiveController {
 
   #getRootNode: () => Node;
   #getHash: (el: Element) => string | null;
+  #onIntersection?: () => void;
 
   get #linkChildren(): Element[] {
     return Array.from(this.host.querySelectorAll(this.#tagNames.join(',')))
@@ -95,6 +100,7 @@ export class ScrollSpyController implements ReactiveController {
     this.#threshold = options.threshold ?? 0.85;
     this.#getRootNode = () => options.rootNode ?? host.getRootNode();
     this.#getHash = options?.getHash ?? ((el: Element) => el.getAttribute('href'));
+    this.#onIntersection = options?.onIntersection;
   }
 
   hostConnected(): void {
@@ -172,6 +178,7 @@ export class ScrollSpyController implements ReactiveController {
       }
       this.#initializing = false;
     }
+    this.#onIntersection?.();
   }
 
   /**

From bc2d5e9a3e17d5ec611d62cf87736f3ff73d0930 Mon Sep 17 00:00:00 2001
From: Benny Powers <web@bennypowers.com>
Date: Thu, 3 Apr 2025 16:02:42 +0300
Subject: [PATCH 3/3] fix(core): scroll-spy select last element on end scroll

---
 .../controllers/scroll-spy-controller.ts       | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/core/pfe-core/controllers/scroll-spy-controller.ts b/core/pfe-core/controllers/scroll-spy-controller.ts
index a5473ae24b..24dd1e60cb 100644
--- a/core/pfe-core/controllers/scroll-spy-controller.ts
+++ b/core/pfe-core/controllers/scroll-spy-controller.ts
@@ -30,6 +30,18 @@ export interface ScrollSpyControllerOptions extends IntersectionObserverInit {
 }
 
 export class ScrollSpyController implements ReactiveController {
+  static #instances = new Set<ScrollSpyController>;
+
+  static {
+    addEventListener('scroll', () => {
+      if (Math.round(window.innerHeight + window.scrollY) >= document.body.scrollHeight) {
+        this.#instances.forEach(ssc => {
+          ssc.#setActive(ssc.#linkChildren.at(-1));
+        });
+      }
+    }, { passive: true });
+  }
+
   #tagNames: string[];
   #activeAttribute: string;
 
@@ -104,9 +116,15 @@ export class ScrollSpyController implements ReactiveController {
   }
 
   hostConnected(): void {
+    ScrollSpyController.#instances.add(this);
     this.#initIo();
   }
 
+  hostDisconnected(): void {
+    ScrollSpyController.#instances.delete(this);
+    this.#io?.disconnect();
+  }
+
   #initializing = true;
 
   async #initIo() {