frontend/src/components/TagDetailSidebar.tsx

@@ -76,7 +76,7 @@ export default (({ post }: Props) => {
   return (
       <SidebarComponent>
 	<TagSearch/>
-	<motion.div layout>
+	<motion.div key={post?.id ?? 0} layout>
 	  {CATEGORIES.map ((cat: Category) => cat in tags && (
 	      <motion.div layout className="my-3" key={cat}>
 		<SubsectionTitle>{categoryNames[cat]}</SubsectionTitle>

frontend/src/components/TopNav.tsx

@@ -1,7 +1,7 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
 import { AnimatePresence, motion } from 'framer-motion'
-import { Fragment, useState, useEffect } from 'react'
+import { Fragment, useEffect, useLayoutEffect, useRef, useState } from 'react'
 import { Link, useLocation } from 'react-router-dom'
 
 import Separator from '@/components/MenuSeparator'
@@ -20,9 +20,31 @@ type Props = { user: User | null }
 export default (({ user }: Props) => {
   const location = useLocation ()
 
+  const itemRefs = useRef<(HTMLAnchorElement | null)[]> ([])
+  const navRef = useRef<HTMLDivElement | null> (null)
+
+  const measure = () => {
+    const nav = navRef.current
+    const el = itemRefs.current[activeIdx]
+    if (!(nav) || !(el) || activeIdx < 0)
+      return
+
+    const navRect = nav.getBoundingClientRect ()
+    const elRect = el.getBoundingClientRect ()
+
+    setHl ({ left:    elRect.left - navRect.left,
+	     width:   elRect.width,
+	     visible: true })
+  }
+
+  const [hl, setHl] = useState<{ left: number; width: number; visible: boolean }> ({
+      left:     0,
+      width:    0,
+      visible:  false })
   const [menuOpen, setMenuOpen] = useState (false)
   const [openItemIdx, setOpenItemIdx] = useState (-1)
   const [postCount, setPostCount] = useState<number | null> (null)
+  const [subDir, setSubDir] = useState<(-1) | 1> (1)
   const [wikiId, setWikiId] = useState<number | null> (WikiIdBus.get ())
 
   const wikiPageFlg = Boolean (/^\/wiki\/(?!new|changes)[^\/]+/.test (location.pathname) && wikiId)
@@ -54,11 +76,38 @@ export default (({ user }: Props) => {
 	  { name: 'お前', to: `/users/${ user?.id }`, visible: false },
 	  { name: '設定', to: '/users/settings', visible: Boolean (user) }] }]
 
+  const activeIdx = menu.findIndex (item => location.pathname.startsWith (item.base || item.to))
+
+  const prevActiveIdxRef = useRef<number> (activeIdx)
+
+  useLayoutEffect (() => {
+    if (activeIdx < 0)
+      return
+
+    const raf = requestAnimationFrame (measure)
+    const onResize = () => requestAnimationFrame (measure)
+
+    addEventListener ('resize', onResize)
+    return () => {
+      cancelAnimationFrame (raf)
+      removeEventListener ('resize', onResize)
+    }
+  }, [activeIdx])
+
   useEffect (() => {
     const unsubscribe = WikiIdBus.subscribe (setWikiId)
     return () => unsubscribe ()
   }, [])
 
+  useEffect (() => {
+    const prev = prevActiveIdxRef.current
+    if (prev !== activeIdx)
+      {
+	setSubDir (activeIdx > prev ? 1 : -1)
+	prevActiveIdxRef.current = activeIdx
+      }
+  }, [activeIdx])
+
   useEffect (() => {
     setMenuOpen (false)
     setOpenItemIdx (menu.findIndex (item => (
@@ -99,16 +148,28 @@ export default (({ user }: Props) => {
 	      ぼざクリ タグ広場
 	    </Link>
 
-	    {menu.map ((item, i) => (
+	    <div ref={navRef} className="relative hidden md:flex h-full items-center">
-		<Link key={i}
+	      <div aria-hidden
-		      to={item.to}
+		   className={cn ('absolute top-1/2 -translate-y-1/2 h-full rounded-md',
-		      className={cn ('hidden md:flex h-full items-center',
+				  'bg-yellow-200 dark:bg-red-950',
-				     (location.pathname.startsWith (item.base || item.to)
+				  'transition-[transform,width,opacity] duration-200 ease-out')}
-				      ? 'bg-yellow-200 dark:bg-red-950 px-4 font-bold'
+		   style={{ width:      hl.width,
-				      : 'px-2'))}>
+			    transform:  `translate(${ hl.left }px, -50%)`,
-		  {item.name}
+			    opacity:    hl.visible ? 1 : 0 }}/>
-		</Link>
+
-	    ))}
+	      {menu.map ((item, i) => (
+		  <Link key={i}
+			to={item.to}
+			ref={el => {
+			  itemRefs.current[i] = el
+			}}
+			className={cn ('relative z-10 flex h-full items-center px-5',
+				       ((i === openItemIdx)
+					? 'font-bold'
+					: 'opacity-90 hover:opacity-100'))}>
+		    {item.name}
+		  </Link>))}
+	    </div>
 	  </div>
 
 	  <TopNavUser user={user}/>
@@ -126,15 +187,28 @@ export default (({ user }: Props) => {
 	</nav>
 
 	<div className="hidden md:flex bg-yellow-200 dark:bg-red-950
-			items-center w-full min-h-[40px] px-3">
+			items-center w-full min-h-[40px] px-3 overflow-hidden">
-	  {menu.find (item => location.pathname.startsWith (item.base || item.to))?.subMenu
+	  <AnimatePresence mode="wait" initial={false}>
-	   .filter (item => item.visible ?? true)
+	    <motion.div
-	   .map ((item, i) => 'component' in item ? item.component : (
+		key={activeIdx}
-	      <Link key={i}
+		className="flex items-center"
-		    to={item.to}
+		initial={{ y: subDir * 24, opacity: 0 }}
-		    className="h-full flex items-center px-3">
+		animate={{ y: 0, opacity: 1 }}
-		{item.name}
+		exit={{ y: subDir * 24, opacity: 0 }}
-	      </Link>))}
+		transition={{ duration: .1, ease: 'easeOut' }}>
+	      {(menu[activeIdx]?.subMenu ?? [])
+	       .filter (item => item.visible ?? true)
+	       .map ((item, i) => (
+		  'component' in item
+		  ? <Fragment key={`c-${ i }`}>{item.component}</Fragment>
+		  : (
+		      <Link key={`l-${ i }`}
+			    to={item.to}
+			    className="h-full flex items-center px-3">
+			{item.name}
+		      </Link>)))}
+	    </motion.div>
+	  </AnimatePresence>
 	</div>
 
 	<AnimatePresence initial={false}>
@@ -167,16 +241,38 @@ export default (({ user }: Props) => {
 			    }}>
 			{item.name}
 		      </Link>
-		      {i === openItemIdx && (
+
-			  item.subMenu
+		      <AnimatePresence initial={false}>
-			  .filter (subItem => subItem.visible ?? true)
+			{i === openItemIdx && (
-			  .map ((subItem, j) => 'component' in subItem ? subItem.component : (
+			    <motion.div
-			      <Link key={j}
+				key={`sp-sub-${ i }`}
-				    to={subItem.to}
+				className="w-full bg-yellow-50 dark:bg-red-950"
-				    className="w-full min-h-[36px] flex items-center pl-12
+				variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
-					       bg-yellow-50 dark:bg-red-950">
+						      height:   0,
-				{subItem.name}
+						      opacity:  0 },
-			      </Link>)))}
+					    open:   { clipPath: 'inset(0 0 0% 0)',
+						      height:   'auto',
+						      opacity:  1 } }}
+				initial="closed"
+				animate="open"
+				exit="closed"
+				transition={{ duration: .2, ease: 'easeOut' }}>
+			      {item.subMenu
+			       .filter (subItem => subItem.visible ?? true)
+			       .map ((subItem, j) => (
+				  'component' in subItem
+				  ? (
+				      <Fragment key={`sp-c-${ i }-${ j }`}>
+					{subItem.component}
+				      </Fragment>)
+				  : (
+				      <Link key={`sp-l-${ i }-${ j }`}
+					    to={subItem.to}
+					    className="w-full min-h-[36px] flex items-center pl-12">
+					{subItem.name}
+				      </Link>)))}
+			    </motion.div>)}
+		      </AnimatePresence>
 		    </Fragment>))}
 		<TopNavUser user={user} sp/>
 		<Separator/>