wp-calypso/packages/data-stores/src/add-ons/hooks/use-add-on-checkout-link.ts

import { useCallback } from '@wordpress/element';
import * as Site from '../../site';

/**
 * Returns a function that will return a formatted checkout link for the given add-on and quantity.
 * E.g. https://wordpress.com/checkout/<siteSlug>/<addOnSlug>>:-q-<quantity>
 * @returns {Function} A function returnig a formatted checkout link for the given add-on and quantity
 */

const useAddOnCheckoutLink = (): ( (
	selectedSiteId: Site.SiteDetails[ 'ID' ] | null,
	addOnSlug: string,
	quantity?: number
) => string ) => {
	const checkoutLinkCallback = useCallback(
		(
			selectedSiteId: Site.SiteDetails[ 'ID' ] | null,
			addOnSlug: string,
			quantity?: number
		): string => {
			// If no site is provided, return the checkout link with the add-on (will render site-selector).
			if ( ! selectedSiteId ) {
				return `/checkout/${ addOnSlug }`;
			}

			const checkoutLinkFormat = `/checkout/${ selectedSiteId }/${ addOnSlug }`;

			if ( quantity ) {
				return checkoutLinkFormat + `:-q-${ quantity }`;
			}
			return checkoutLinkFormat;
		},
		[]
	);
	return checkoutLinkCallback;
};

export default useAddOnCheckoutLink;