# ssr-prerender: Configure Static Prerendering and ISR

## Priority: MEDIUM

## Explanation

Static prerendering generates HTML at build time for pages that don't require request-time data. Incremental Static Regeneration (ISR) extends this by revalidating cached pages on a schedule. Use these for better performance and lower server costs.

## Bad Example

```tsx
// SSR for completely static content - wasteful
export const Route = createFileRoute('/about')({
  loader: async () => {
    // Fetching static content on every request
    const content = await fetchAboutPageContent()
    return { content }
  },
})

// Or no caching headers for semi-static content
export const Route = createFileRoute('/blog/$slug')({
  loader: async ({ params }) => {
    const post = await fetchPost(params.slug)
    return { post }
    // Every request hits the database
  },
})
```

## Good Example: Static Prerendering

```tsx
// app.config.ts
import { defineConfig } from '@tanstack/react-start/config'

export default defineConfig({
  server: {
    prerender: {
      // Routes to prerender at build time
      routes: [
        '/',
        '/about',
        '/contact',
        '/pricing',
      ],
      // Or crawl from root
      crawlLinks: true,
    },
  },
})

// routes/about.tsx - Will be prerendered
export const Route = createFileRoute('/about')({
  loader: async () => {
    // Runs at BUILD time, not request time
    const content = await fetchAboutPageContent()
    return { content }
  },
  component: AboutPage,
})
```

## Good Example: Dynamic Prerendering

```tsx
// app.config.ts
export default defineConfig({
  server: {
    prerender: {
      // Generate routes dynamically
      routes: async () => {
        const posts = await db.posts.findMany({
          where: { published: true },
          select: { slug: true },
        })

        return [
          '/',
          '/blog',
          ...posts.map(p => `/blog/${p.slug}`),
        ]
      },
    },
  },
})
```

## Good Example: ISR with Revalidation

```tsx
// routes/blog/$slug.tsx
import { createFileRoute } from '@tanstack/react-router'
import { setHeaders } from '@tanstack/react-start/server'

export const Route = createFileRoute('/blog/$slug')({
  loader: async ({ params }) => {
    const post = await fetchPost(params.slug)

    // ISR: Cache for 60 seconds, then revalidate
    setHeaders({
      'Cache-Control': 'public, s-maxage=60, stale-while-revalidate=300',
    })

    return { post }
  },
  component: BlogPost,
})

// First request: SSR and cache
// Next 60 seconds: Serve cached version
// After 60 seconds: Serve stale, revalidate in background
// After 300 seconds: Full SSR again
```

## Good Example: Hybrid Static/Dynamic

```tsx
// routes/products.tsx - Prerendered
export const Route = createFileRoute('/products')({
  loader: async () => {
    // Featured products - prerendered at build
    const featured = await fetchFeaturedProducts()
    return { featured }
  },
})

// routes/products/$productId.tsx - ISR
export const Route = createFileRoute('/products/$productId')({
  loader: async ({ params }) => {
    const product = await fetchProduct(params.productId)

    if (!product) throw notFound()

    // Cache product pages for 5 minutes
    setHeaders({
      'Cache-Control': 'public, s-maxage=300, stale-while-revalidate=600',
    })

    return { product }
  },
})

// routes/cart.tsx - Always SSR (user-specific)
export const Route = createFileRoute('/cart')({
  loader: async ({ context }) => {
    // No caching - user-specific data
    setHeaders({
      'Cache-Control': 'private, no-store',
    })

    const cart = await fetchUserCart(context.user.id)
    return { cart }
  },
})
```

## Good Example: On-Demand Revalidation

```tsx
// API route to trigger revalidation
// app/routes/api/revalidate.ts
export const APIRoute = createAPIFileRoute('/api/revalidate')({
  POST: async ({ request }) => {
    const { secret, path } = await request.json()

    // Verify secret
    if (secret !== process.env.REVALIDATE_SECRET) {
      return json({ error: 'Invalid secret' }, { status: 401 })
    }

    // Trigger revalidation (implementation depends on hosting)
    await revalidatePath(path)

    return json({ revalidated: true, path })
  },
})

// Usage: POST /api/revalidate { "secret": "...", "path": "/blog/my-post" }
```

## Cache-Control Directives

| Directive | Meaning |
|-----------|---------|
| `s-maxage=N` | CDN cache duration (seconds) |
| `max-age=N` | Browser cache duration |
| `stale-while-revalidate=N` | Serve stale while fetching fresh |
| `private` | Don't cache on CDN (user-specific) |
| `no-store` | Never cache |

## Context

- Prerendering happens at build time - no request context
- ISR requires CDN/edge support (Vercel, Cloudflare, etc.)
- Use prerendering for truly static pages (about, pricing)
- Use ISR for content that changes but not per-request
- Always SSR for user-specific or real-time data
- Test with production builds - dev server is always SSR
