/**
 * Extension SD Fetcher
 *
 * Fetches and caches Extension StructureDefinitions from remote registries.
 * This enables HAPI-level validation of extensions by loading their SDs.
 *
 * Key Features:
 * - Fetch Extension SDs from packages.fhir.org
 * - Cache with configurable TTL
 * - Support for multiple registries
 * - Fallback behavior for unavailable SDs
 */
import type { StructureDefinition } from '../core/structure-definition-types';
export interface ExtensionSDCache {
    sd: StructureDefinition | null;
    fetchedAt: number;
    error?: string;
}
export interface FetcherConfig {
    /** Registry URLs to try */
    registries: string[];
    /** TTL for cached entries in ms */
    cacheTtlMs: number;
    /** Timeout for fetch requests */
    timeoutMs: number;
    /** Whether to fetch remote SDs */
    enableRemoteFetch: boolean;
}
export declare class ExtensionSDFetcher {
    private cache;
    private config;
    private inFlightRequests;
    constructor(config?: Partial<FetcherConfig>);
    /**
     * Fetch an extension StructureDefinition by URL
     */
    fetch(extensionUrl: string): Promise<StructureDefinition | null>;
    /**
     * Try fetching from multiple registries
     */
    private fetchFromRegistries;
    /**
     * Fetch from a specific registry
     */
    private fetchFromRegistry;
    /**
     * Extract package info from extension URL
     */
    private extractPackageInfo;
    /**
     * Preload common extensions
     */
    preloadCommon(): Promise<void>;
    /**
     * Clear cache
     */
    clearCache(): void;
    /**
     * Get cache stats
     */
    getCacheStats(): {
        size: number;
        hitRate: number;
    };
}
export declare const extensionSDFetcher: ExtensionSDFetcher;
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