feat: implement Topic Feed UI/UX enhancement

src/app/topics/[slug]/page.tsx

@@ -0,0 +1,27 @@
+import type { Metadata } from 'next';
+import TopicFeed from '@/components/social/TopicFeed';
+
+interface TopicPageProps {
+  params: Promise<{ slug: string }>;
+}
+
+export async function generateMetadata({ params }: TopicPageProps): Promise<Metadata> {
+  const { slug } = await params;
+  const name = slug.replace(/-/g, ' ');
+  return {
+    title: `#${name} · TeachLink`,
+    description: `Explore posts and discussions about ${name} on TeachLink.`,
+  };
+}
+
+export default async function TopicPage({ params }: TopicPageProps) {
+  const { slug } = await params;
+
+  return (
+    <main className="min-h-screen bg-gray-50 dark:bg-gray-950">
+      <div className="max-w-2xl mx-auto px-4 py-8">
+        <TopicFeed slug={slug} />
+      </div>
+    </main>
+  );
+}

src/components/social/TopicFeed.tsx

@@ -0,0 +1,216 @@
+'use client';
+
+import { useEffect, useRef } from 'react';
+import Image from 'next/image';
+import { UserCircle, Heart, MessageCircle, TrendingUp, Clock, ArrowUp } from 'lucide-react';
+import { useTopicFeed, type SortOption } from '@/hooks/useTopicFeed';
+import { getRelativeTime, formatFollowerCount } from '@/utils/socialUtils';
+
+// ─── Skeleton ─────────────────────────────────────────────────────────────────
+
+function PostSkeleton() {
+  return (
+    <div className="p-4 animate-pulse" aria-hidden="true">
+      <div className="flex gap-3">
+        <div className="w-9 h-9 rounded-full bg-gray-200 dark:bg-gray-700 shrink-0" />
+        <div className="flex-1 space-y-2">
+          <div className="h-4 bg-gray-200 dark:bg-gray-700 rounded w-1/4" />
+          <div className="h-5 bg-gray-200 dark:bg-gray-700 rounded w-3/4" />
+          <div className="h-3 bg-gray-200 dark:bg-gray-700 rounded w-full" />
+          <div className="h-3 bg-gray-200 dark:bg-gray-700 rounded w-2/3" />
+        </div>
+      </div>
+    </div>
+  );
+}
+
+// ─── Sort controls ─────────────────────────────────────────────────────────────
+
+const SORT_OPTIONS: { value: SortOption; label: string; icon: React.ReactNode }[] = [
+  { value: 'latest', label: 'Latest', icon: <Clock className="w-3.5 h-3.5" /> },
+  { value: 'popular', label: 'Popular', icon: <TrendingUp className="w-3.5 h-3.5" /> },
+  { value: 'oldest', label: 'Oldest', icon: <ArrowUp className="w-3.5 h-3.5" /> },
+];
+
+interface SortBarProps {
+  current: SortOption;
+  onChange: (s: SortOption) => void;
+}
+
+function SortBar({ current, onChange }: SortBarProps) {
+  return (
+    <div className="flex gap-1 p-1 bg-gray-100 dark:bg-gray-800 rounded-lg" role="group" aria-label="Sort posts">
+      {SORT_OPTIONS.map(({ value, label, icon }) => (
+        <button
+          key={value}
+          onClick={() => onChange(value)}
+          aria-pressed={current === value}
+          className={`flex items-center gap-1.5 px-3 py-1.5 rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-blue-500 ${
+            current === value
+              ? 'bg-white dark:bg-gray-700 text-gray-900 dark:text-white shadow-sm'
+              : 'text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-200'
+          }`}
+        >
+          {icon}
+          {label}
+        </button>
+      ))}
+    </div>
+  );
+}
+
+// ─── TopicFeed ─────────────────────────────────────────────────────────────────
+
+interface TopicFeedProps {
+  slug: string;
+}
+
+export default function TopicFeed({ slug }: TopicFeedProps) {
+  const { topic, posts, loading, loadingMore, hasMore, sort, setSort, loadMore, error } =
+    useTopicFeed(slug);
+  const sentinelRef = useRef<HTMLDivElement>(null);
+
+  // Infinite scroll via IntersectionObserver
+  useEffect(() => {
+    const el = sentinelRef.current;
+    if (!el) return;
+    const observer = new IntersectionObserver(
+      ([entry]) => {
+        if (entry.isIntersecting) loadMore();
+      },
+      { threshold: 0.1 },
+    );
+    observer.observe(el);
+    return () => observer.disconnect();
+  }, [loadMore]);
+
+  return (
+    <div className="space-y-4">
+      {/* Topic header */}
+      <div className="bg-white dark:bg-gray-900 rounded-xl border border-gray-200 dark:border-gray-700 p-5">
+        {loading && !topic ? (
+          <div className="animate-pulse space-y-2">
+            <div className="h-6 bg-gray-200 dark:bg-gray-700 rounded w-1/3" />
+            <div className="h-4 bg-gray-200 dark:bg-gray-700 rounded w-2/3" />
+          </div>
+        ) : topic ? (
+          <>
+            <h1 className="text-xl font-bold text-gray-900 dark:text-white">#{topic.name}</h1>
+            {topic.description && (
+              <p className="mt-1 text-sm text-gray-600 dark:text-gray-400">{topic.description}</p>
+            )}
+            <div className="mt-3 flex gap-4 text-sm text-gray-500 dark:text-gray-400">
+              <span>
+                <strong className="text-gray-900 dark:text-white">
+                  {formatFollowerCount(topic.postCount)}
+                </strong>{' '}
+                posts
+              </span>
+              <span>
+                <strong className="text-gray-900 dark:text-white">
+                  {formatFollowerCount(topic.followerCount)}
+                </strong>{' '}
+                followers
+              </span>
+            </div>
+          </>
+        ) : null}
+      </div>
+
+      {/* Sort bar */}
+      <div className="flex items-center justify-between">
+        <SortBar current={sort} onChange={setSort} />
+      </div>
+
+      {/* Posts list */}
+      <div className="bg-white dark:bg-gray-900 rounded-xl border border-gray-200 dark:border-gray-700 divide-y divide-gray-100 dark:divide-gray-800">
+        {/* Initial loading skeletons */}
+        {loading &&
+          posts.length === 0 &&
+          Array.from({ length: 5 }).map((_, i) => <PostSkeleton key={i} />)}
+
+        {/* Error state */}
+        {error && !loading && (
+          <div className="p-8 text-center" role="alert">
+            <p className="text-sm text-red-600 dark:text-red-400">{error}</p>
+          </div>
+        )}
+
+        {/* Empty state */}
+        {!loading && !error && posts.length === 0 && (
+          <div className="p-10 text-center">
+            <p className="text-sm text-gray-500 dark:text-gray-400">
+              No posts in this topic yet. Be the first to share!
+            </p>
+          </div>
+        )}
+
+        {/* Post items */}
+        {posts.map((post) => (
+          <article key={post.id} className="p-4 hover:bg-gray-50 dark:hover:bg-gray-800/50 transition-colors">
+            <div className="flex gap-3">
+              {post.authorAvatar ? (
+                <Image
+                  src={post.authorAvatar}
+                  alt={post.authorName}
+                  width={36}
+                  height={36}
+                  className="w-9 h-9 rounded-full object-cover shrink-0"
+                />
+              ) : (
+                <UserCircle className="w-9 h-9 text-gray-400 shrink-0" aria-hidden="true" />
+              )}
+
+              <div className="flex-1 min-w-0">
+                <div className="flex items-center gap-2 text-sm">
+                  <span className="font-medium text-gray-900 dark:text-white">
+                    {post.authorName}
+                  </span>
+                  <span className="text-gray-400 dark:text-gray-500">·</span>
+                  <time
+                    dateTime={post.createdAt.toISOString()}
+                    className="text-gray-500 dark:text-gray-400"
+                  >
+                    {getRelativeTime(post.createdAt)}
+                  </time>
+                </div>
+
+                <h2 className="mt-1 text-base font-semibold text-gray-900 dark:text-white leading-snug">
+                  {post.title}
+                </h2>
+
+                <p className="mt-1 text-sm text-gray-600 dark:text-gray-400 line-clamp-3">
+                  {post.body}
+                </p>
+
+                <div className="mt-3 flex items-center gap-4 text-sm text-gray-500 dark:text-gray-400">
+                  <span className="flex items-center gap-1">
+                    <Heart className="w-4 h-4" aria-hidden="true" />
+                    <span>{formatFollowerCount(post.likes)}</span>
+                    <span className="sr-only">likes</span>
+                  </span>
+                  <span className="flex items-center gap-1">
+                    <MessageCircle className="w-4 h-4" aria-hidden="true" />
+                    <span>{formatFollowerCount(post.commentCount)}</span>
+                    <span className="sr-only">comments</span>
+                  </span>
+                </div>
+              </div>
+            </div>
+          </article>
+        ))}
+
+        {/* Infinite scroll sentinel */}
+        {hasMore && <div ref={sentinelRef} className="h-4" aria-hidden="true" />}
+
+        {/* Load-more skeleton */}
+        {loadingMore && <PostSkeleton />}
+
+        {/* End of feed */}
+        {!loading && !hasMore && posts.length > 0 && (
+          <p className="py-4 text-center text-xs text-gray-400">You&apos;ve reached the end</p>
+        )}
+      </div>
+    </div>
+  );
+}

src/hooks/useTopicFeed.ts

@@ -0,0 +1,90 @@
+'use client';
+
+import { useState, useEffect, useCallback } from 'react';
+import { apiClient } from '@/lib/api';
+import type { Topic, TopicPost } from '@/utils/socialUtils';
+
+export type SortOption = 'latest' | 'popular' | 'oldest';
+
+interface UseTopicFeedReturn {
+  topic: Topic | null;
+  posts: TopicPost[];
+  loading: boolean;
+  loadingMore: boolean;
+  hasMore: boolean;
+  sort: SortOption;
+  setSort: (s: SortOption) => void;
+  loadMore: () => void;
+  error: string | null;
+}
+
+export function useTopicFeed(slug: string): UseTopicFeedReturn {
+  const [topic, setTopic] = useState<Topic | null>(null);
+  const [posts, setPosts] = useState<TopicPost[]>([]);
+  const [cursor, setCursor] = useState<string | undefined>(undefined);
+  const [hasMore, setHasMore] = useState(true);
+  const [loading, setLoading] = useState(true);
+  const [loadingMore, setLoadingMore] = useState(false);
+  const [sort, setSort] = useState<SortOption>('latest');
+  const [error, setError] = useState<string | null>(null);
+
+  const fetchPosts = useCallback(
+    async (nextCursor?: string, currentSort: SortOption = sort) => {
+      const isInitial = !nextCursor;
+      if (isInitial) setLoading(true);
+      else setLoadingMore(true);
+      setError(null);
+
+      try {
+        const params = new URLSearchParams({ limit: '20', sort: currentSort });
+        if (nextCursor) params.set('cursor', nextCursor);
+
+        const [topicRes, postsRes] = await Promise.all([
+          isInitial
+            ? apiClient.get<Topic>(`/api/topics/${slug}`)
+            : Promise.resolve(null as unknown as Topic),
+          apiClient.get<{ data: TopicPost[]; nextCursor?: string }>(
+            `/api/topics/${slug}/posts?${params}`,
+          ),
+        ]);
+
+        if (isInitial && topicRes) setTopic(topicRes);
+
+        const normalized = postsRes.data.map((p) => ({
+          ...p,
+          createdAt: new Date(p.createdAt),
+        }));
+
+        setPosts((prev) => (isInitial ? normalized : [...prev, ...normalized]));
+        setCursor(postsRes.nextCursor);
+        setHasMore(!!postsRes.nextCursor);
+      } catch {
+        setError('Failed to load topic feed. Please try again.');
+        setHasMore(false);
+      } finally {
+        setLoading(false);
+        setLoadingMore(false);
+      }
+    },
+    [slug, sort],
+  );
+
+  // Reset and reload when slug or sort changes
+  useEffect(() => {
+    setPosts([]);
+    setCursor(undefined);
+    setHasMore(true);
+    fetchPosts(undefined, sort);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [slug, sort]);
+
+  const loadMore = useCallback(() => {
+    if (!loadingMore && hasMore && cursor) fetchPosts(cursor);
+  }, [loadingMore, hasMore, cursor, fetchPosts]);
+
+  const handleSetSort = useCallback((s: SortOption) => {
+    setSort(s);
+  }, []);
+
+  return { topic, posts, loading, loadingMore, hasMore, sort, setSort: handleSetSort, loadMore, error };
+}

src/utils/socialUtils.ts

@@ -1,3 +1,24 @@
+export interface Topic {
+  slug: string;
+  name: string;
+  description?: string;
+  postCount: number;
+  followerCount: number;
+}
+
+export interface TopicPost {
+  id: string;
+  authorId: string;
+  authorName: string;
+  authorAvatar?: string;
+  title: string;
+  body: string;
+  topicSlug: string;
+  likes: number;
+  commentCount: number;
+  createdAt: Date;
+}
+
 export interface Activity {
   id: string;
   actorId: string;