From cd98d6637f4740f9384a3642ab7d32700ddb4394 Mon Sep 17 00:00:00 2001
From: Adrian Bonpin <adrianbonpin@gmail.com>
Date: Fri, 1 May 2026 09:34:04 +0800
Subject: [PATCH] feat: add ChapterNav component with mobile support

---
 components/updates/chapter-nav.tsx | 95 ++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 components/updates/chapter-nav.tsx

diff --git a/components/updates/chapter-nav.tsx b/components/updates/chapter-nav.tsx
new file mode 100644
index 0000000..74cecc9
--- /dev/null
+++ b/components/updates/chapter-nav.tsx
@@ -0,0 +1,95 @@
+"use client"
+
+import { useEffect, useState } from "react"
+import { ListIcon } from "lucide-react"
+import type { UpdateHeading } from "@/lib/updates"
+
+export function ChapterNav({
+  headings,
+}: {
+  headings: UpdateHeading[]
+}) {
+  const [activeId, setActiveId] = useState<string>(headings[0]?.id ?? "")
+  const [mobileOpen, setMobileOpen] = useState(false)
+
+  useEffect(() => {
+    const observers: IntersectionObserver[] = []
+
+    headings.forEach((heading) => {
+      const element = document.getElementById(heading.id)
+      if (!element) return
+
+      const observer = new IntersectionObserver(
+        (entries) => {
+          entries.forEach((entry) => {
+            if (entry.isIntersecting) {
+              setActiveId(heading.id)
+            }
+          })
+        },
+        {
+          rootMargin: "-20% 0px -70% 0px",
+        },
+      )
+      observer.observe(element)
+      observers.push(observer)
+    })
+
+    return () => {
+      observers.forEach((observer) => observer.disconnect())
+    }
+  }, [headings])
+
+  if (headings.length === 0) return null
+
+  return (
+    <>
+      {/* Mobile toggle button */}
+      <button
+        onClick={() => setMobileOpen(!mobileOpen)}
+        className="fixed bottom-4 right-4 z-50 md:hidden flex items-center justify-center w-10 h-10 rounded-full bg-background border border-border shadow-lg hover:border-border-active transition-colors cursor-pointer"
+        aria-label="Toggle chapter navigation"
+      >
+        <ListIcon className="w-5 h-5" />
+      </button>
+
+      {/* Mobile dropdown */}
+      {mobileOpen && (
+        <div
+          className="fixed inset-0 z-45 md:hidden"
+          onClick={() => setMobileOpen(false)}
+        />
+      )}
+      <nav
+        className={`fixed bottom-16 right-4 z-50 md:z-auto md:static md:block max-h-[50vh] md:max-h-none overflow-y-auto bg-background border border-border rounded-lg p-3 shadow-lg md:shadow-none md:rounded-none md:border-0 md:p-0 md:bg-transparent transition-all md:transition-none ${
+          mobileOpen
+            ? "block opacity-100"
+            : "hidden md:block opacity-0 md:opacity-100"
+        }`}
+      >
+        <h4 className="text-xs uppercase text-text/40 font-semibold mb-2 hidden md:block">
+          Chapters
+        </h4>
+        <ul className="flex flex-col gap-1">
+          {headings.map((heading) => (
+            <li key={heading.id}>
+              <a
+                href={`#${heading.id}`}
+                onClick={() => setMobileOpen(false)}
+                className={`block text-sm py-1 transition-colors ${
+                  heading.level === 3 ? "pl-3" : ""
+                } ${
+                  activeId === heading.id
+                    ? "text-primary font-medium"
+                    : "text-text/60 hover:text-text"
+                }`}
+              >
+                {heading.text}
+              </a>
+            </li>
+          ))}
+        </ul>
+      </nav>
+    </>
+  )
+}