perf: cache and prefetch course pages

lib/hooks/useCourses.ts

@@ -1,14 +1,24 @@
 'use client'
 
-import { useState, useEffect, useCallback } from 'react'
+import { useCallback, useEffect, useRef, useState } from 'react'
+
+export interface CourseTag {
+  id: string
+  name: string
+  color?: string | null
+  _count?: { courseTags: number }
+}
 
 export interface Course {
   id: string
   name: string
+  displayName?: string | null
   slug: string
   thumbnail: string | null
   description: string | null
   path: string
+  favorited?: boolean
+  tags?: CourseTag[]
   createdAt: string
   updatedAt: string
   _count: { modules: number; lessons: number }
@@ -22,7 +32,8 @@ export interface Course {
 }
 
 interface CoursesResponse {
-  courses: any[]
+  courses: Course[]
+  tags: CourseTag[]
   pagination: {
     page: number
     limit: number
@@ -42,9 +53,36 @@ interface UseCoursesOptions {
   initialSortOrder?: string
 }
 
+interface CacheEntry {
+  data: CoursesResponse
+  expiresAt: number
+}
+
+const CACHE_TTL_MS = 20_000
+const MAX_CACHE_ENTRIES = 24
+const responseCache = new Map<string, CacheEntry>()
+
+function readCache(key: string): CoursesResponse | null {
+  const cached = responseCache.get(key)
+  if (!cached) return null
+  if (cached.expiresAt <= Date.now()) {
+    responseCache.delete(key)
+    return null
+  }
+  return cached.data
+}
+
+function writeCache(key: string, data: CoursesResponse) {
+  if (responseCache.size >= MAX_CACHE_ENTRIES) {
+    const oldestKey = responseCache.keys().next().value
+    if (oldestKey) responseCache.delete(oldestKey)
+  }
+  responseCache.set(key, { data, expiresAt: Date.now() + CACHE_TTL_MS })
+}
+
 export function useCourses(options: UseCoursesOptions = {}) {
-  const [courses, setCourses] = useState<any[]>([])
-  const [tags, setTags] = useState<any[]>([])
+  const [courses, setCourses] = useState<Course[]>([])
+  const [tags, setTags] = useState<CourseTag[]>([])
   const [loading, setLoading] = useState(false)
   const [error, setError] = useState<string | null>(null)
   const [pagination, setPagination] = useState({
@@ -60,19 +98,38 @@ export function useCourses(options: UseCoursesOptions = {}) {
   const [sortBy, setSortBy] = useState(options.initialSortBy || 'updatedAt')
   const [sortOrder, setSortOrder] = useState(options.initialSortOrder || 'desc')
   const [debouncedSearch, setDebouncedSearch] = useState(options.initialSearch || '')
+  const abortRef = useRef<AbortController | null>(null)
+  const requestIdRef = useRef(0)
+  const hasDataRef = useRef(false)
 
-  // Debounce search
   useEffect(() => {
-    const timer = setTimeout(() => {
+    const timer = window.setTimeout(() => {
       setDebouncedSearch(search)
-      setPagination(prev => ({ ...prev, page: 1 }))
-    }, 300)
-    return () => clearTimeout(timer)
+      setPagination((previous) => ({ ...previous, page: 1 }))
+    }, 250)
+    return () => window.clearTimeout(timer)
   }, [search])
 
-  const fetchCourses = useCallback(async () => {
-    setLoading(true)
-    setError(null)
+  const applyResponse = useCallback((data: CoursesResponse) => {
+    hasDataRef.current = true
+    setCourses(data.courses)
+    setTags(data.tags || [])
+    setPagination((previous) => ({
+      ...previous,
+      page: data.pagination.page,
+      limit: data.pagination.limit,
+      total: data.pagination.total,
+      totalPages: data.pagination.totalPages,
+      hasNext: data.pagination.hasNext,
+      hasPrev: data.pagination.hasPrev,
+    }))
+  }, [])
+
+  const fetchCourses = useCallback(async (force = false) => {
+    abortRef.current?.abort()
+    const controller = new AbortController()
+    abortRef.current = controller
+    const requestId = ++requestIdRef.current
 
     const params = new URLSearchParams({
       page: pagination.page.toString(),
@@ -82,72 +139,118 @@ export function useCourses(options: UseCoursesOptions = {}) {
       sortBy,
       sortOrder,
     })
+    const requestKey = params.toString()
+    const cached = force ? null : readCache(requestKey)
+
+    if (cached) {
+      applyResponse(cached)
+      setLoading(false)
+      setError(null)
+      return
+    }
+
+    if (!hasDataRef.current) setLoading(true)
+    setError(null)
 
     try {
-      const response = await fetch(`/api/courses?${params.toString()}`)
+      const response = await fetch(`/api/courses?${requestKey}`, {
+        signal: controller.signal,
+        headers: { Accept: 'application/json' },
+      })
       if (!response.ok) {
         throw new Error('Failed to fetch courses')
       }
-      const data = await response.json()
-      setCourses(data.courses)
-      setTags(data.tags || [])
-      setPagination(prev => ({
-        ...prev,
-        total: data.pagination.total,
-        totalPages: data.pagination.totalPages,
-        hasNext: data.pagination.hasNext,
-        hasPrev: data.pagination.hasPrev,
-      }))
-    } catch (err) {
-      setError(err instanceof Error ? err.message : 'Failed to fetch courses')
+
+      const data = await response.json() as CoursesResponse
+      if (requestId !== requestIdRef.current) return
+
+      writeCache(requestKey, data)
+      applyResponse(data)
+
+      if (data.pagination.hasNext) {
+        const nextParams = new URLSearchParams(params)
+        nextParams.set('page', String(data.pagination.page + 1))
+        const nextKey = nextParams.toString()
+
+        if (!readCache(nextKey)) {
+          window.setTimeout(() => {
+            void fetch(`/api/courses?${nextKey}`, {
+              headers: { Accept: 'application/json' },
+            })
+              .then((nextResponse) => nextResponse.ok ? nextResponse.json() : null)
+              .then((nextData: CoursesResponse | null) => {
+                if (nextData) writeCache(nextKey, nextData)
+              })
+              .catch(() => undefined)
+          }, 150)
+        }
+      }
+    } catch (caughtError) {
+      if (caughtError instanceof DOMException && caughtError.name === 'AbortError') return
+      if (requestId !== requestIdRef.current) return
+      setError(caughtError instanceof Error ? caughtError.message : 'Failed to fetch courses')
     } finally {
-      setLoading(false)
+      if (requestId === requestIdRef.current) setLoading(false)
     }
-  }, [pagination.page, pagination.limit, debouncedSearch, filter, sortBy, sortOrder])
+  }, [
+    applyResponse,
+    pagination.page,
+    pagination.limit,
+    debouncedSearch,
+    filter,
+    sortBy,
+    sortOrder,
+  ])
 
   useEffect(() => {
-    fetchCourses()
+    void fetchCourses()
+    return () => abortRef.current?.abort()
   }, [fetchCourses])
 
   const goToPage = (page: number) => {
-    setPagination(prev => ({ ...prev, page }))
+    setPagination((previous) => ({ ...previous, page: Math.max(1, page) }))
   }
 
   const nextPage = () => {
     if (pagination.hasNext) {
-      setPagination(prev => ({ ...prev, page: prev.page + 1 }))
+      setPagination((previous) => ({ ...previous, page: previous.page + 1 }))
     }
   }
 
   const prevPage = () => {
     if (pagination.hasPrev) {
-      setPagination(prev => ({ ...prev, page: prev.page - 1 }))
+      setPagination((previous) => ({ ...previous, page: Math.max(1, previous.page - 1) }))
     }
   }
 
   const changeLimit = (limit: number) => {
-    setPagination(prev => ({ ...prev, limit, page: 1 }))
+    setPagination((previous) => ({ ...previous, limit, page: 1 }))
   }
 
-  const handleSearch = (value: string) => {
-    setSearch(value)
-  }
+  const handleSearch = (value: string) => setSearch(value)
 
   const handleFilter = (value: string) => {
     setFilter(value)
-    setPagination(prev => ({ ...prev, page: 1 }))
+    setPagination((previous) => ({ ...previous, page: 1 }))
   }
 
   const handleSort = (field: string) => {
     setSortBy(field)
-    setPagination(prev => ({ ...prev, page: 1 }))
+    setPagination((previous) => ({ ...previous, page: 1 }))
+  }
+
+  const handleSortOrder = (value: string) => {
+    setSortOrder(value === 'asc' ? 'asc' : 'desc')
+    setPagination((previous) => ({ ...previous, page: 1 }))
   }
 
   const toggleSortOrder = () => {
-    setSortOrder(prev => prev === 'asc' ? 'desc' : 'asc')
-    setPagination(prev => ({ ...prev, page: 1 }))
+    setSortOrder((previous) => previous === 'asc' ? 'desc' : 'asc')
+    setPagination((previous) => ({ ...previous, page: 1 }))
   }
 
+  const refetch = useCallback(() => fetchCourses(true), [fetchCourses])
+
   return {
     courses,
     tags,
@@ -161,12 +264,12 @@ export function useCourses(options: UseCoursesOptions = {}) {
     sortBy,
     sortOrder,
     setSortBy: handleSort,
-    setSortOrder: toggleSortOrder,
+    setSortOrder: handleSortOrder,
     toggleSortOrder,
     goToPage,
     nextPage,
     prevPage,
     changeLimit,
-    refetch: fetchCourses,
+    refetch,
   }
-}
+}