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// next.config.ts
import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  cacheComponents: true,
};

export default nextConfig;

// lib/cache/tags.ts (skeleton — full template in assets/tags.ts)

export const CACHE_TAGS = {
  // Collection tags — one per logical data group, always present.
  [collection]: "[collection]",

  // Entity tag factories — only when a mutation targets a single entry.
  [entity]: (id: string | number) => `[entity]:${id}`,
} as const;

// lib/cache/revalidate.ts
"use server";

import { updateTag } from "next/cache";
import { CACHE_TAGS } from "./tags";

function updateTags(tags: string[]) {
  for (const tag of tags) updateTag(tag);
}

// Bulk — any entry in the collection changed.
export async function revalidate[Collection]Cache() {
  updateTags([CACHE_TAGS.[collection]]);
}

// Surgical — one specific entry changed.
// Only write this if `CACHE_TAGS.[entity]` factory exists in the registry.
export async function revalidate[Entity]Cache(id: string | number) {
  updateTags([
    CACHE_TAGS.[collection], // always invalidate the parent collection too
    CACHE_TAGS.[entity](id),
  ]);
}

// lib/data/[domain].ts
import { cacheLife, cacheTag } from "next/cache";
import { CACHE_TAGS } from "@/lib/cache/tags";

const BASE_URL = process.env.API_BASE_URL!;

// Good: collection fetch.
export async function get[Collection]() {
  "use cache";
  cacheLife("hours");
  cacheTag(CACHE_TAGS.[collection]);

  const res = await fetch(`${BASE_URL}/[endpoint]`);
  return res.json();
}

// Good: entity fetch.
export async function get[Entity](id: string) {
  "use cache";
  cacheLife("hours");
  cacheTag(CACHE_TAGS.[collection]);
  // Add CACHE_TAGS.[entity](id) only if a mutation calls updateTag on this entry.

  const res = await fetch(`${BASE_URL}/[endpoint]/${id}`);
  return res.json();
}

// Bad: fetching in a page component bypasses caching and invalidation.
export default async function Page() {
  const res = await fetch("/api/items");
  const data = await res.json();
  return <View data={data} />;
}

Page component (sync, orchestration only — no data fetching)
  ├── Static shell (layout, nav — no data)
  ├── <Suspense> → cached shared content
  └── <Suspense> → dynamic personalized content

// app/[route]/page.tsx
import { Suspense } from "react";
import { cacheLife, cacheTag } from "next/cache";
import { CACHE_TAGS } from "@/lib/cache/tags";
import { get[Collection] } from "@/lib/data/[domain]";

export default function AnyPage() {
  return (
    <>
      <StaticShell />

      <Suspense fallback={<SharedSkeleton />}>
        <SharedContent />
      </Suspense>

      <Suspense fallback={<PersonalizedSkeleton />}>
        <PersonalizedSection />
      </Suspense>
    </>
  );
}

async function SharedContent() {
  "use cache";
  cacheLife("hours");
  cacheTag(CACHE_TAGS.[collection]);

  const data = await get[Collection]();
  return <[Collection]List data={data} />;
}

// app/[domain]/[id]/page.tsx
import { Suspense } from "react";
import { cacheLife, cacheTag } from "next/cache";
import { CACHE_TAGS } from "@/lib/cache/tags";
import { get[Entity] } from "@/lib/data/[domain]";

export default function EntityPage({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  return (
    <Suspense fallback={<EntitySkeleton />}>
      <EntityDetail params={params} />
    </Suspense>
  );
}

async function EntityDetail({
  params,
}: {
  params: Promise<{ id: string }>;
}) {
  const { id } = await params;
  return <CachedEntityView id={id} />;
}

async function CachedEntityView({ id }: { id: string }) {
  "use cache";
  cacheLife("hours");
  cacheTag(CACHE_TAGS.[collection]);
  // Add CACHE_TAGS.[entity](id) only if a mutation needs surgical invalidation.

  const item = await get[Entity](id);
  return <[Entity]View item={item} />;
}

// app/[route]/page.tsx
import { cacheLife, cacheTag } from "next/cache";
import { CACHE_TAGS } from "@/lib/cache/tags";
import { get[Collection]ByFilter } from "@/lib/data/[domain]";
import SuspenseOnSearchParams from "@/components/SuspenseOnSearchParams";

export default function FilteredPage({
  searchParams,
}: {
  searchParams: Promise<Record<string, string>>;
}) {
  return (
    <SuspenseOnSearchParams fallback={<FilteredListSkeleton />}>
      <FilteredList searchParams={searchParams} />
    </SuspenseOnSearchParams>
  );
}

async function FilteredList({
  searchParams,
}: {
  searchParams: Promise<Record<string, string>>;
}) {
  "use cache";
  cacheLife("minutes");
  cacheTag(CACHE_TAGS.[collection]);
  // searchParams is an argument → auto-keyed per unique param combination.

  const { q = "", page = "1" } = await searchParams;
  return await get[Collection]ByFilter(q, page);
}

// app/actions/[domain].ts
"use server";

import {
  revalidate[Collection]Cache,
  revalidate[Entity]Cache,
} from "@/lib/cache/revalidate";

export async function create[Entity](payload: unknown) {
  await db.[entity].create(payload);
  await revalidate[Collection]Cache();
}

export async function update[Entity](id: string | number, payload: unknown) {
  await db.[entity].update(id, payload);
  await revalidate[Entity]Cache(id); // requires the surgical utility to be exported
}