import { Schema, ValidationOptions } from 'joi';
import { formatError } from './formatter';
import { ErrorMessages } from './types';
import { Request, Response, NextFunction } from 'express';
/**
 * Enhanced Type Safety for Validation Results
 * This interface ensures that validation results are strongly typed.
 */
export interface ValidationResult<T> {
    value: T;
    error?: ReturnType<typeof formatError> | null;
}
/**
 * validate
 * Synchronous validation function.
 *
 * Field-Level Error Message Overrides & Custom Error Formatting Options:
 * The error messages are formatted using the provided (or default) error messages.
 * You can supply field-specific messages in the custom messages object. For instance:
 *   { 'name.string.min': 'Name must have at least {#limit} characters.' }
 *
 * @param schema - Joi schema definition.
 * @param input - Data to validate.
 * @param options - Optional Joi validation options.
 * @param messages - Custom error message overrides.
 * @returns ValidationResult<T>
 */
export declare function validate<T>(schema: Schema, input: any, messages?: ErrorMessages, options?: ValidationOptions): ValidationResult<T>;
/**
 * validateAsync
 * Async Validation Support:
 * Handles asynchronous Joi validation, which is useful when validations involve async operations,
 * such as database lookups or external API calls.
 *
 * @param schema - Joi schema definition.
 * @param input - Data to validate.
 * @param options - Optional Joi validation options.
 * @param messages - Custom error message overrides.
 * @returns Promise resolving to ValidationResult<T>
 */
export declare function validateAsync<T>(schema: Schema, input: any, messages?: ErrorMessages, options?: ValidationOptions): Promise<ValidationResult<T>>;
/**
 * validateMiddleware
 * Express Middleware for Validation:
 * Returns an Express middleware that validates req.body against the provided schema.
 * If validation fails, it sends a 400 response with formatted errors.
 *
 * @param schema - Joi schema definition.
 * @param messages - Custom error message overrides.
 * @returns Express middleware function.
 */
export declare function validateMiddleware(schema: Schema, messages?: ErrorMessages): (req: Request, res: Response, next: NextFunction) => Response<any, Record<string, any>> | undefined;