/**
 * Configuration loader supporting config files (.usernamerc) and environment variables
 */
import type { ConfigOptions } from './types.js';
/**
 * Loads configuration from multiple sources following precedence:
 * 1. CLI flags (passed directly, not handled here)
 * 2. Environment variables (USERNAME_CHECKER_*)
 * 3. Config file (.usernamerc)
 * 4. Defaults
 */
export declare class ConfigLoader {
    private static readonly ENV_PREFIX;
    /**
     * Load configuration from all available sources
     */
    static loadConfig(): ConfigOptions;
    /**
     * Find config file in priority order:
     * 1. Current working directory
     * 2. Home directory
     * 3. XDG_CONFIG_HOME (Linux/macOS standard)
     */
    private static findConfigFile;
    /**
     * Parse config file (JSON format)
     */
    private static parseConfigFile;
    /**
     * Load configuration from environment variables
     * Supported variables:
     * - USERNAME_CHECKER_TIMEOUT
     * - USERNAME_CHECKER_CONCURRENCY (maxConcurrency)
     * - USERNAME_CHECKER_MAX_CONCURRENCY
     * - USERNAME_CHECKER_RETRIES
     * - USERNAME_CHECKER_NSFW (true/false)
     * - USERNAME_CHECKER_EXCLUDED (includeExcluded, true/false)
     * - USERNAME_CHECKER_TOR (true/false)
     * - USERNAME_CHECKER_PROXY
     * - USERNAME_CHECKER_FORMAT
     * - USERNAME_CHECKER_CACHE_TYPE
     * - USERNAME_CHECKER_CACHE_TTL
     * - USERNAME_CHECKER_DEFAULT_SITES (comma-separated)
     */
    private static loadEnvironmentVariables;
    /**
     * Validate and normalize config object
     */
    private static validateConfig;
    /**
     * Create sample config file content
     */
    static getSampleConfigContent(): string;
}