/**
 * Represents a set of database operations for an in-memory database.
 *
 * These kinds of databases are key value pairs similar to redis,
 * local storage, sessions storage, etc.
 */
export interface IZDatabaseMemory {
    /**
     * Gets the value of a specific key in the database.
     *
     * @param key -
     *        The key to retrieve.
     *
     * @returns
     *        The value of the given key, null if no such value
     *        exists and no fallback was provided.
     */
    read<T>(key: string): Promise<T | null>;
    /**
     * Gets the value of a specific key in the database.
     *
     * @param key -
     *        The key to retrieve.
     * @param fallback -
     *        The fallback value.  If the key does not exist
     *        in the database, then this will be inserted
     *        automatically.
     *
     * @returns
     *        The value of the given key or the inserted fallback value
     *        if the key does not exist.
     */
    read<T>(key: string, fallback: T): Promise<T>;
    /**
     * Creates or updates a key value.
     *
     * @param key -
     *        The key to update.
     * @param value -
     *        The value to set.
     *
     * @returns
     *        The value that was written.
     */
    upsert<T>(key: string, value: T): Promise<T>;
    /**
     * Deletes a key in the database or deletes all keys in the database.
     *
     * @param key -
     *        The key to delete.  If this is undefined, then all
     *        keys should be deleted.
     */
    delete(key?: string): Promise<void>;
}