/** Where cached values live. `get` and `set` may be synchronous or asynchronous. */
export interface CacheAdapter<T = unknown> {
    /** Returns the cached value, or `undefined` for a miss or an expired entry. */
    get(key: string): Promise<T | undefined> | T | undefined;
    /** Stores a value, for `ttlSeconds` when given. */
    set(key: string, value: T, ttlSeconds?: number): Promise<void> | void;
    /** Removes a value. Returns true when one was removed. */
    delete?(key: string): Promise<boolean> | boolean;
    /** Removes every value. */
    clear?(): Promise<void> | void;
}
/** Cache values in process memory. Expired entries are dropped when read. */
export declare class MemoryCacheAdapter<T = unknown> implements CacheAdapter<T> {
    private entries;
    /** Returns the cached value, or `undefined` for a miss or an expired entry. */
    get(key: string): T | undefined;
    /** Stores a value. Defaults to 5 minutes. */
    set(key: string, value: T, ttlSeconds?: number): void;
    /** Removes a value. */
    delete(key: string): boolean;
    /** Removes every value. */
    clear(): void;
}
/** The Redis commands the cache adapter needs, in `ioredis` argument order. */
export interface RedisLikeClient {
    /** Reads a key. */
    get(key: string): Promise<string | null> | string | null;
    /** Writes a key, with `EX` and a TTL in seconds. */
    set(key: string, value: string, mode?: string, ttlSeconds?: number): Promise<unknown> | unknown;
    /** Deletes a key. */
    del?(key: string): Promise<number> | number;
}
/** Cache values in Redis, shared across processes. Values are stored as JSON under a key prefix. */
export declare class RedisCacheAdapter<T = unknown> implements CacheAdapter<T> {
    private client;
    private prefix;
    constructor(client: RedisLikeClient, prefix?: string);
    /** Returns the cached value, or `undefined` for a miss. */
    get(key: string): Promise<T | undefined>;
    /** Stores a value. Defaults to 5 minutes. */
    set(key: string, value: T, ttlSeconds?: number): Promise<void>;
    /** Removes a value. Returns false when the client has no `del`. */
    delete(key: string): Promise<boolean>;
}
/**
 * The part of a SQLite database handle the cache adapter needs, as `better-sqlite3` provides it.
 */
export interface SQLiteLikeDatabase {
    /** Prepares a statement. */
    prepare(sql: string): {
        get?: (...args: unknown[]) => unknown;
        run?: (...args: unknown[]) => unknown;
    };
    /** Runs SQL without results, used to create the table. */
    exec?(sql: string): unknown;
}
/** Cache values in a SQLite table, for a single-machine cache that survives restarts. */
export declare class SQLiteCacheAdapter<T = unknown> implements CacheAdapter<T> {
    private db;
    private table;
    constructor(db: SQLiteLikeDatabase, table?: string);
    /** Returns the cached value, or `undefined` for a miss or an expired entry. */
    get(key: string): T | undefined;
    /** Stores a value. Defaults to 5 minutes. */
    set(key: string, value: T, ttlSeconds?: number): void;
    /**
     * Removes a value. Always returns true, since SQLite does not report whether the row existed
     * here.
     */
    delete(key: string): boolean;
    /** Removes every value. */
    clear(): void;
}