/**
 * Convert a price from USD to target currency.
 */
export declare function convertPrice(priceUsd: number, rate: number): number;
/**
 * Format a price with currency symbol.
 * Examples: "1 234 ₽", "$12.34", "€12.34"
 */
export declare function formatPrice(amount: number, currency?: string): string;
/**
 * Generate a unique idempotency key for checkout requests.
 */
export declare function generateIdempotencyKey(): string;
import type { FeeMode } from "./types";
/**
 * Client-side PREVIEW of the surcharge fee for a payment method, BIT-EXACT
 * with the server (apps/api site-payment-fees.ts `computeFee` +
 * `resolveCheckoutCharge`). Lets a storefront render the "Комиссия платёжной
 * системы" line at method-selection time without a round-trip.
 *
 * Matches the server byte-for-byte:
 *   fee   = max(0, round2(goods * percent / 100 + fixed))     // computeFee
 *   gross = round2(goods + fee) when surcharge, else goods    // resolveCheckoutCharge
 *   round2 = Math.round(x * 100) / 100
 *
 * The order of operations is load-bearing: `(goods * percent) / 100 + fixed`,
 * THEN round2 — NOT `goods * (percent / 100)`. e.g. goods=23, percent=2.5:
 * `(23 * 2.5) / 100` = 0.575 (float 0.5749…) → round2 = 0.57, but the naive
 * `23 * (2.5 / 100)` = 0.5750000000000001 → round2 = 0.58 — a kopeck off, and
 * the previewed button would disagree with the actual charge.
 *
 * `applies` is true ONLY for `feeMode === "surcharge"`; absorb/included/
 * undefined ⇒ `applies:false, fee:0, gross:goods` (matches the server default
 * `feeMode ?? "included"`). Source of truth stays the checkout response
 * `payment.fee` — this is preview-only. NEVER use it for topup (always net).
 */
export declare function estimateSurcharge(input: {
    goods: number;
    feePercent?: number;
    feeFixed?: number;
    feeMode?: FeeMode;
}): {
    applies: boolean;
    fee: number;
    gross: number;
};
/**
 * Clamp a persisted marketing-visit id to a positive integer, or undefined.
 * Storefronts keep mvFirst/mvLast in localStorage — a user can tamper with
 * them, and a garbage value must be DROPPED client-side rather than sent
 * (a non-numeric field would 422 the whole auth call / checkout).
 */
export declare function sanitizeMvId(value: unknown): number | undefined;