/**
 * A timestamp in milliseconds elapsed since the epoch
 */
export type Timestamp = number;
export interface CacheEntry {
    /**
     * The serialized value of the entry. A cache handler consumes this stream in
     * `set` and persists what it delivers. A handler can buffer the stream, or it
     * can pipe it to its storage as chunks arrive. Two rules apply either way:
     *
     * - A handler must return a new stream from every `get`.
     * - A handler must not retain the stream after `set` resolves.
     *
     * A stream can be read one time only. A second reader of the same stream gets
     * no data, or an error while the first reader holds the lock. A retained
     * stream also keeps a reference to the async context of the request that
     * created it, which keeps the state of that request reachable for as long as
     * the entry lives.
     *
     * The same applies to the `pendingEntry` promise that `set` receives. A
     * handler must not put that promise in a map that outlives the request.
     *
     * The stream can error and deliver partial data. Each handler decides whether
     * it keeps the partial entry or discards it.
     */
    value: ReadableStream<Uint8Array>;
    /**
     * The tags configured for the entry excluding soft tags
     */
    tags: string[];
    /**
     * This is for the client, not used to calculate cache entry expiration
     * [duration in seconds]
     */
    stale: number;
    /**
     * When the cache entry was created [timestamp in milliseconds]
     */
    timestamp: Timestamp;
    /**
     * How long the entry is allowed to be used (should be longer than revalidate)
     * [duration in seconds]
     *
     * This is the hard limit. Next.js compares it against `timestamp` on every
     * read and treats a too-old entry as a miss, so a handler does not need to
     * check the age of an entry before it returns one. The dev server raises the
     * limit to five minutes when `expire` is shorter, to keep reloads fast.
     */
    expire: number;
    /**
     * How long until the entry should be revalidated [duration in seconds]
     *
     * An entry that is past `revalidate` but within `expire` is still served, and
     * Next.js generates a fresh one in the background. A negative value always
     * lies in the past, so it forces that background refresh on the next read.
     * The built-in handler returns `-1` for an entry whose tag is stale, which
     * serves the entry one more time and replaces it.
     */
    revalidate: number;
}
export interface CacheHandler {
    /**
     * Retrieve a cache entry for the given cache key, if available. Will return
     * undefined if there's nothing stored, or if the given soft tags are stale.
     *
     * Each call returns a new `value` stream over the stored bytes. See
     * `CacheEntry.value`.
     */
    get(cacheKey: string, softTags: string[]): Promise<undefined | CacheEntry>;
    /**
     * Store a cache entry for the given cache key. When this is called, the entry
     * may still be pending, i.e. its value stream may still be written to. So it
     * needs to be awaited first. If a `get` for the same cache key is called,
     * before the pending entry is complete, the cache handler must wait for the
     * `set` operation to finish, before returning the entry, instead of returning
     * undefined.
     *
     * The handler takes ownership of the entry's `value` stream, and consumes it
     * exactly once. See `CacheEntry.value`.
     *
     * The handler also owns eviction. Next.js never removes an entry from the
     * store, so the store needs a mechanism of its own, such as a time to live
     * from `expire`, or a size-bounded LRU.
     */
    set(cacheKey: string, pendingEntry: Promise<CacheEntry>): Promise<void>;
    /**
     * This function is called once per request, before the first cache read for
     * this handler's kind. A request that reads nothing from this handler does
     * not call it. If applicable, it should communicate with the tags service to
     * refresh the local tags manifest accordingly.
     */
    refreshTags(): Promise<void>;
    /**
     * This function is called for each set of soft tags that are relevant at the
     * start of a request. The result is the maximum timestamp of a revalidate
     * event for the tags. Returns `0` if none of the tags were ever revalidated.
     * Returns `Infinity` if the soft tags are supposed to be passed into the
     * `get` method instead to be checked for expiration.
     */
    getExpiration(tags: string[]): Promise<Timestamp>;
    /**
     * This function is called when tags are revalidated/expired. If applicable,
     * it should update the tags manifest accordingly.
     */
    updateTags(tags: string[], durations?: {
        expire?: number;
    }): Promise<void>;
}