refactor: SidebarNav uses usePathname and Link instead of IntersectionObserver

src/widgets/Navigation/ui/SidebarNav.test.tsx

@@ -2,21 +2,23 @@ import { render, screen } from '@testing-library/react';
 import type { NavItem } from '../model/types';
 import { SidebarNav } from './SidebarNav';
 
+vi.mock('next/navigation', () => ({
+  usePathname: vi.fn(),
+}));
+
+import { usePathname } from 'next/navigation';
+
 const ITEMS: NavItem[] = [
   { id: 'bio', label: 'Bio', number: '01' },
   { id: 'work', label: 'Work', number: '02' },
 ];
 
-beforeEach(() => {
-  global.IntersectionObserver = class {
-    observe = vi.fn();
-    disconnect = vi.fn();
-    unobserve = vi.fn();
-  } as unknown as typeof IntersectionObserver;
-});
-
 describe('SidebarNav', () => {
   describe('rendering', () => {
+    beforeEach(() => {
+      vi.mocked(usePathname).mockReturnValue('/bio');
+    });
+
     it('renders a nav element', () => {
       render(<SidebarNav items={ITEMS} />);
       expect(screen.getByRole('navigation')).toBeInTheDocument();
@@ -50,10 +52,33 @@ describe('SidebarNav', () => {
       expect(screen.getByRole('link', { name: 'Email' })).toBeInTheDocument();
     });
 
-    it('renders a button for each item', () => {
+    it('renders a link for each nav item', () => {
       render(<SidebarNav items={ITEMS} />);
-      const buttons = screen.getAllByRole('button');
-      expect(buttons.length).toBeGreaterThanOrEqual(ITEMS.length);
+      expect(screen.getByRole('link', { name: /Bio/i })).toBeInTheDocument();
+      expect(screen.getByRole('link', { name: /Work/i })).toBeInTheDocument();
+    });
+  });
+
+  describe('active state', () => {
+    it('marks matching pathname item as active (no opacity-40)', () => {
+      vi.mocked(usePathname).mockReturnValue('/bio');
+      render(<SidebarNav items={ITEMS} />);
+      const activeLink = screen.getByRole('link', { name: /Bio/i });
+      expect(activeLink).not.toHaveClass('opacity-40');
+    });
+
+    it('marks non-matching item as inactive (opacity-40)', () => {
+      vi.mocked(usePathname).mockReturnValue('/bio');
+      render(<SidebarNav items={ITEMS} />);
+      const inactiveLink = screen.getByRole('link', { name: /Work/i });
+      expect(inactiveLink).toHaveClass('opacity-40');
+    });
+
+    it('marks first item active at root path', () => {
+      vi.mocked(usePathname).mockReturnValue('/');
+      render(<SidebarNav items={ITEMS} />);
+      const firstLink = screen.getByRole('link', { name: /Bio/i });
+      expect(firstLink).not.toHaveClass('opacity-40');
     });
   });
 });

src/widgets/Navigation/ui/SidebarNav.tsx

@@ -1,6 +1,7 @@
 'use client';
 
-import { useEffect, useState } from 'react';
+import Link from 'next/link';
+import { usePathname } from 'next/navigation';
 import { CONTACT_LINKS, cn } from '$shared/lib';
 import type { NavItem } from '../model/types';
 
@@ -13,41 +14,23 @@ interface Props {
 
 /**
  * Fixed sidebar navigation, visible on lg+ screens.
+ * Active section determined by current URL pathname.
  */
 export function SidebarNav({ items }: Props) {
-  const [activeSection, setActiveSection] = useState('bio');
-
-  useEffect(() => {
-    const observer = new IntersectionObserver(
-      (entries) => {
-        entries.forEach((entry) => {
-          if (entry.isIntersecting) {
-            setActiveSection(entry.target.id);
-          }
-        });
-      },
-      { rootMargin: '-20% 0px -70% 0px', threshold: 0 },
-    );
-
-    items.forEach((item) => {
-      const el = document.getElementById(item.id);
-      if (el) {
-        observer.observe(el);
-      }
-    });
-
-    return () => observer.disconnect();
-  }, [items]);
+  const pathname = usePathname();
 
   /**
-   * Scrolls to the section by id with a 40px offset.
+   * An item is active when its slug matches the current pathname,
+   * or when the pathname is root and it is the first item.
    */
-  function scrollToSection(id: string) {
-    const el = document.getElementById(id);
-    if (el) {
-      const top = el.getBoundingClientRect().top + window.scrollY - 40;
-      window.scrollTo({ top, behavior: 'smooth' });
+  function isActive(item: NavItem): boolean {
+    if (pathname === `/${item.id}`) {
+      return true;
     }
+    if (pathname === '/' && items[0]?.id === item.id) {
+      return true;
+    }
+    return false;
   }
 
   return (
@@ -60,27 +43,23 @@ export function SidebarNav({ items }: Props) {
           </div>
         </div>
 
-        {items.map((item) => {
-          const isActive = activeSection === item.id;
-          return (
-            <button
-              type="button"
-              key={item.id}
-              onClick={() => scrollToSection(item.id)}
-              className={cn(
-                'w-full text-left brutal-border bg-ochre-clay px-6 py-4 transition-all duration-300',
-                isActive
-                  ? 'shadow-[12px_12px_0_var(--carbon-black)] opacity-100 translate-x-0'
-                  : 'opacity-40 shadow-none hover:opacity-60',
-              )}
-            >
-              <div className="flex items-baseline gap-4">
-                <span className="text-sm opacity-60">{item.number}</span>
-                <span className="font-heading text-xl font-black">{item.label}</span>
-              </div>
-            </button>
-          );
-        })}
+        {items.map((item) => (
+          <Link
+            key={item.id}
+            href={`/${item.id}`}
+            className={cn(
+              'block w-full text-left brutal-border bg-ochre-clay px-6 py-4 transition-all duration-300',
+              isActive(item)
+                ? 'shadow-[12px_12px_0_var(--carbon-black)] opacity-100 translate-x-0'
+                : 'opacity-40 shadow-none hover:opacity-60',
+            )}
+          >
+            <div className="flex items-baseline gap-4">
+              <span className="text-sm opacity-60">{item.number}</span>
+              <span className="font-heading text-xl font-black">{item.label}</span>
+            </div>
+          </Link>
+        ))}
 
         <div className="mt-12 pt-12 brutal-border-top">
           <p className="text-sm uppercase tracking-wider mb-4 opacity-60">Quick Links</p>