/**
 * @fileoverview Service for interacting with the ClinicalTrials.gov API.
 * This module provides a singleton class `ClinicalTrialsGovService` that encapsulates
 * all network requests to the ClinicalTrials.gov API, handles response validation,
 * and implements backing up of API responses to the local filesystem.
 * @module src/services/clinical-trials-gov/ClinicalTrialsGovService
 */
import { type RequestContext } from "../../utils/index.js";
import type { FieldNode, PagedStudies, Study } from "./types.js";
/**
 * A service class to interact with the ClinicalTrials.gov API.
 * It handles request construction, API communication, and response backup.
 */
export declare class ClinicalTrialsGovService {
    private static instance;
    /**
     * Private constructor to prevent direct instantiation.
     */
    private constructor();
    /**
     * Returns the singleton instance of the ClinicalTrialsGovService.
     * @returns The singleton instance.
     */
    static getInstance(): ClinicalTrialsGovService;
    /**
     * Fetches a single study by its NCT ID, with optional parameters.
     * @param nctId - The NCT ID of the study.
     * @param context - The request context for logging.
     * @param options - Optional parameters for the fetch request.
     * @param options.fields - A list of specific top-level fields to return.
     * @param options.markupFormat - The format for rich text fields ('markdown' or 'legacy').
     * @returns A promise that resolves with the study data.
     */
    fetchStudy(nctId: string, context: RequestContext, options?: {
        fields?: string[];
        markupFormat?: "markdown" | "legacy";
    }): Promise<Study>;
    /**
     * Searches for studies based on a set of query parameters.
     * @param params - The query parameters for the search.
     * @param context - The request context for logging.
     * @returns A promise that resolves with a paged list of studies.
     */
    listStudies(params: Record<string, unknown>, context: RequestContext): Promise<PagedStudies>;
    /**
     * Fetches the study metadata.
     * @param params - Parameters for filtering metadata.
     * @param context - The request context for logging.
     * @returns A promise that resolves with the field node data.
     */
    getStudyMetadata(params: {
        includeIndexedOnly?: boolean;
        includeHistoricOnly?: boolean;
    }, context: RequestContext): Promise<FieldNode[]>;
    /**
     * Fetches API statistics.
     * @param statType - The type of statistics to retrieve.
     * @param params - Additional parameters for the statistics request.
     * @param context - The request context for logging.
     * @returns A promise that resolves with the statistical data.
     */
    getApiStats(statType: "studySize" | "fieldValues" | "listFieldSizes", params: {
        fields?: string[];
        types?: string[];
    }, context: RequestContext): Promise<unknown>;
    /**
     * A generic fetch method that handles backing up the response.
     * It always fetches live data and writes it to a backup file if the data path is configured.
     * @param url - The URL to fetch.
     * @param fileName - The file name to use for the backup.
     * @param context - The request context for logging.
     * @returns A promise that resolves with the fetched data.
     */
    private fetchAndBackup;
}