withKVCache.ts

export const DEFAULT_CACHE_SECONDS = 15
/**
 * We're **not** using upstash or the Vercel KV SDK here to avoid package conflicts
 * instead we're using vercel KV's REST API directly: https://vercel.com/docs/storage/vercel-kv/rest-api
 */

const createClient = <T>({ token, url }: { token: string; url: string }) => {
  return {
    get: async (key: string): Promise<T | null> => {
      const result = await (
        await fetch(url, {
          body: `["GET", "${key}"]`,
          headers: {
            Authorization: `Bearer ${token}`,
          },
          method: 'POST',
        })
      ).json()
      if (result.result) {
        return JSON.parse(result.result)
      } else {
        return null
      }
    },
    set: async (
      key: string,
      value: T,
      options: {
        ex?: number
      },
    ) => {
      const result = await (
        await fetch(
          `${url}/set/${key}?EX=${options.ex || DEFAULT_CACHE_SECONDS}`,
          {
            body: JSON.stringify(value),
            headers: {
              Authorization: `Bearer ${token}`,
            },
            method: 'POST',
          },
        )
      ).json()
      return result.result
    },
  }
}

/**
 * @param fetcher Function a function that returns the data to be cached
 * @param cacheKey string the cache key
 * @param options object
 * @param options.ex number the number of seconds to cache the data
 *
 * @returns Promise<any> the data from the fetcher
 * todo: could be generically typed
 */
export const withKVCache = async <T>(
  fetcher: () => Promise<T>,
  cacheKey: string,
  options: { ex: number } = { ex: DEFAULT_CACHE_SECONDS },
) => {
  const kvClient =
    process.env.KV_REST_API_URL && process.env.KV_REST_API_TOKEN
      ? createClient<T>({
          token: process.env.KV_REST_API_TOKEN,
          url: process.env.KV_REST_API_URL,
        })
      : undefined

  if (!kvClient) {
    return fetcher()
  }

  const cacheResult = await kvClient.get(cacheKey)
  if (cacheResult) {
    // eslint-disable-next-line no-console
    console.debug(`[KV_CACHE:HIT] ${cacheKey}`, cacheResult)
    return cacheResult
  }

  const fetchResult = await fetcher()
  const kvResult = await kvClient.set(cacheKey, fetchResult, {
    ex: options.ex,
  })
  // eslint-disable-next-line no-console
  console.debug(
    `[KV_CACHE:MISS] ${cacheKey} [ex:${options.ex}], cached: ${kvResult}`,
  )
  return fetchResult
}