/**
 * Google Cloud Storage controller (works with GCS and Firebase Storage)
 *
 * The `@google-cloud/storage` package is loaded lazily so it remains an
 * optional peer dependency — users who don't need GCS never pay for the
 * import cost or need it installed.
 */
import { StorageController, GCSStorageConfig } from "./types";
import { UploadFileProps, UploadFileResult, DownloadConfig, StorageListResult } from "@rebasepro/types";
/**
 * Google Cloud Storage implementation of `StorageController`.
 *
 * Works with standard GCS buckets **and** Firebase Storage buckets
 * (e.g. `"my-project.appspot.com"`).
 */
export declare class GCSStorageController implements StorageController {
    private config;
    private client;
    constructor(config: GCSStorageConfig);
    private getClient;
    getType(): "gcs";
    putObject({ file, key, metadata, bucket }: UploadFileProps): Promise<UploadFileResult>;
    getSignedUrl(key: string, bucket?: string): Promise<DownloadConfig>;
    getObject(key: string, bucket?: string): Promise<File | null>;
    deleteObject(key: string, bucket?: string): Promise<void>;
    listObjects(prefix: string, options?: {
        bucket?: string;
        maxResults?: number;
        pageToken?: string;
    }): Promise<StorageListResult>;
    /**
     * Validate file before upload
     */
    private validateFile;
    /**
     * Get the bucket name — either from parameter or config.
     */
    private getBucket;
    /**
     * Flatten nested metadata to string values (GCS custom metadata requirement)
     */
    private flattenMetadata;
}