import type { IAssetAdapter } from "./types";
export interface IFileSystemAdapterOptions {
    directory?: string;
    pathPrefix?: string;
    baseUrl?: string;
    extension?: string;
    fallbackToOrigin?: boolean;
    userAgent?: string | false;
    concurrency?: number;
}
/**
 * Caches image assets on the local filesystem. On `resolve`:
 * - if the file is already cached, returns a local reference;
 * - otherwise enqueues a deduplicated background download and (by default) returns the
 *   origin URL until the file is available, after which subsequent calls return the
 *   local reference.
 *
 * Downloads are best-effort and never throw out of `resolve`. Use `flush` to await all
 * pending downloads (e.g. to warm the cache before rendering).
 */
export declare class FileSystemAdapter implements IAssetAdapter {
    directory: string;
    pathPrefix: string;
    baseUrl: string;
    extension: string;
    fallbackToOrigin: boolean;
    userAgent: string | false;
    concurrency: number;
    private cached;
    private pending;
    private queue;
    private active;
    constructor({ directory, pathPrefix, baseUrl, extension, fallbackToOrigin, userAgent, concurrency, }?: IFileSystemAdapterOptions);
    init(): void;
    private localRef;
    private originUrl;
    private fetchToDisk;
    private next;
    private schedule;
    resolve(filename: string): string;
    flush(): Promise<void>;
}