import type { Response } from 'express'

import { createLogger } from '@/observability/logger'

const logger = createLogger(import.meta.url)

type CacheControlKey = 'cache-control' | 'surrogate-control'

interface CacheControlOptions {

key?: CacheControlKey

immutable?: boolean

staleWhileRevalidate?: number

staleIfError?: number

}

const ONE_MINUTE = 60

const TEN_MINUTES = 10 * ONE_MINUTE

const ONE_HOUR = 60 * ONE_MINUTE

const ONE_DAY = 24 * ONE_HOUR

const ONE_WEEK = 7 * ONE_DAY

const ONE_YEAR = 365 * ONE_DAY

// Return a function you can pass a Response object to and it will set the `Cache-Control` header.

// Max age is in seconds.

// Max age should not be greater than 31536000, per <https://www.ietf.org/rfc/rfc2616.txt>.

function cacheControlFactory(

maxAge: number = 0,

{

key = 'cache-control',

immutable = false,

staleWhileRevalidate = 0,

staleIfError = 0,

}: CacheControlOptions = {},

): (res: Response) => void {

const directives = [

maxAge > 0 && 'public',

maxAge > 0 && `max-age=${maxAge}`,

maxAge <= 0 && 'max-age=0',

maxAge > 0 && immutable && 'immutable',

maxAge <= 0 && 'private',

maxAge <= 0 && 'no-store',

maxAge > 0 && staleWhileRevalidate > 0 && `stale-while-revalidate=${staleWhileRevalidate}`,

maxAge > 0 && staleIfError > 0 && `stale-if-error=${staleIfError}`,

]

.filter(Boolean)

.join(', ')

return (res: Response) => {

if (process.env.NODE_ENV !== 'production' && res.hasHeader('set-cookie') && maxAge) {

logger.warn(

"You can't set a >0 cache-control header AND set-cookie or else the CDN will never respect the cache-control.",

)

}

res.set(key, directives)

}

}

// ### These are roughly in order from shortest to longest. ###

// If you do not want caching.

export const noCacheControl = cacheControlFactory(0)

// Short cache for 4xx errors.

export const errorCacheControl = cacheControlFactory(ONE_MINUTE)

// For default cache control, up to one week in cache but much shorter in browser.

// Most responses are under the default cache control policy.

const browserCacheControl = cacheControlFactory(ONE_MINUTE)

const defaultCDNCacheControl = cacheControlFactory(TEN_MINUTES, {

key: 'surrogate-control',

staleWhileRevalidate: ONE_WEEK,

staleIfError: ONE_WEEK,

})

export function defaultCacheControl(res: Response): void {

browserCacheControl(res)

defaultCDNCacheControl(res)

}

export const searchCacheControl = defaultCacheControl

// For requests where the response can vary between a HTML and Markdown response

// using the accept header.

export function contentTypeCacheControl(res: Response): void {

defaultCacheControl(res)

res.append('vary', 'accept')

}

// Vary on language when needed.

// `x-user-language` is a custom request header derived from `req.cookie:user_language`.

// `accept-language` is truncated to one of our available languages.

// https://bit.ly/3u5UeRN

export function languageCacheControl(res: Response): void {

defaultCacheControl(res)

res.append('vary', 'accept-language, x-user-language')

}

// Vary on both language and version for homepage redirects.

// `x-user-version` is a custom request header derived from `req.cookie:user_version`.

export function languageAndVersionCacheControl(res: Response): void {

defaultCacheControl(res)

res.append('vary', 'accept-language, x-user-language, x-user-version')

}

// Long cache control for versioned assets: such as images, CSS, prebuilt JS.

const assetBrowserCacheControl = cacheControlFactory(TEN_MINUTES)

const assetCDNCacheControl = cacheControlFactory(ONE_WEEK, {

key: 'surrogate-control',

immutable: true,

staleWhileRevalidate: ONE_WEEK,

staleIfError: ONE_WEEK,

})

export function assetCacheControl(res: Response): void {

assetBrowserCacheControl(res)

assetCDNCacheControl(res)

}

// Long caching for archived pages and assets.

const archivedBrowserCacheControl = cacheControlFactory(TEN_MINUTES)

const archivedCDNCacheControl = cacheControlFactory(ONE_YEAR, {

key: 'surrogate-control',

immutable: true,

staleWhileRevalidate: ONE_WEEK,

staleIfError: ONE_WEEK,

})

export function archivedCacheControl(res: Response): void {

archivedBrowserCacheControl(res)

archivedCDNCacheControl(res)

}