/**
 * ===============================================================================
 * ENVIRONMENT VARIABLE UTILITIES
 * ===============================================================================
 *
 * Type-safe utilities for reading environment variables with validation.
 * Extracted from http/config.ts for reuse across the codebase.
 *
 * Usage:
 *   import { getEnv, getEnvNumber, getEnvBoolean } from '../core/config/env.js';
 *
 *   const port = getEnvNumber('PORT', 3000);
 *   const debug = getEnvBoolean('DEBUG', false);
 *   const apiKey = getEnv('API_KEY');  // throws if missing
 *
 * ===============================================================================
 */
/**
 * Get a required environment variable.
 * Throws if the variable is not set and no default is provided.
 *
 * @param key - Environment variable name
 * @param defaultValue - Optional default value
 * @returns The environment variable value
 * @throws Error if variable is missing and no default provided
 */
export declare function getEnv(key: string, defaultValue?: string): string;
/**
 * Get an optional environment variable with a default value.
 * Never throws - always returns a value.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default value if not set
 * @returns The environment variable value or default
 */
export declare function getEnvOptional(key: string, defaultValue: string): string;
/**
 * Get an optional environment variable, returning undefined if not set.
 *
 * @param key - Environment variable name
 * @returns The environment variable value or undefined
 */
export declare function getEnvOrUndefined(key: string): string | undefined;
/**
 * Get an environment variable as a number.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default value if not set
 * @returns Parsed number value
 * @throws Error if value is not a valid number
 */
export declare function getEnvNumber(key: string, defaultValue: number): number;
/**
 * Get an environment variable as a float.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default value if not set
 * @returns Parsed float value
 * @throws Error if value is not a valid number
 */
export declare function getEnvFloat(key: string, defaultValue: number): number;
/**
 * Get an environment variable as a boolean.
 * Accepts: 'true', '1', 'yes', 'on' (case-insensitive) as truthy.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default value if not set
 * @returns Boolean value
 */
export declare function getEnvBoolean(key: string, defaultValue: boolean): boolean;
/**
 * Get an environment variable as a comma-separated list.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default array if not set
 * @param separator - Separator character (default: ',')
 * @returns Array of trimmed strings
 */
export declare function getEnvList(key: string, defaultValue?: string[], separator?: string): string[];
/**
 * Get an environment variable as a JSON object.
 *
 * @param key - Environment variable name
 * @param defaultValue - Default value if not set
 * @returns Parsed JSON object
 * @throws Error if value is not valid JSON
 */
export declare function getEnvJson<T>(key: string, defaultValue: T): T;
/**
 * Get an environment variable constrained to specific values (enum-like).
 *
 * @param key - Environment variable name
 * @param allowedValues - Array of allowed values
 * @param defaultValue - Default value if not set
 * @returns The environment variable value
 * @throws Error if value is not in allowed values
 */
export declare function getEnvEnum<T extends string>(key: string, allowedValues: readonly T[], defaultValue: T): T;
/**
 * Result of environment validation.
 */
export interface EnvValidationResult {
    /** Whether all required variables are present */
    valid: boolean;
    /** List of missing required variables */
    missing: string[];
    /** List of invalid variables (wrong format) */
    invalid: Array<{
        key: string;
        reason: string;
    }>;
}
/**
 * Validate that required environment variables are set.
 *
 * @param required - Array of required variable names
 * @returns Validation result
 */
export declare function validateRequiredEnv(required: string[]): EnvValidationResult;
/**
 * Check if an environment variable is set (non-empty).
 *
 * @param key - Environment variable name
 * @returns true if the variable is set and non-empty
 */
export declare function hasEnv(key: string): boolean;
/**
 * Get the current Node environment.
 *
 * @param defaultEnv - Default environment if NODE_ENV is not set
 * @returns Current environment name
 */
export declare function getNodeEnv(defaultEnv?: 'development' | 'production' | 'test'): 'development' | 'production' | 'test';
/**
 * Check if running in production mode.
 */
export declare function isProduction(): boolean;
/**
 * Check if running in development mode.
 */
export declare function isDevelopment(): boolean;
/**
 * Check if running in test mode.
 */
export declare function isTest(): boolean;
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