modify wordpress rest request

modify_rest_request.php

<?php 

/**
 * @see \WP_REST_Server::respond_to_request();
 *
 * @param \WP_REST_Response|\WP_HTTP_Response|\WP_Error|mixed $response Result to send to the client.
 *                                                                   Usually a WP_REST_Response or WP_Error.
 * @param array                                               $handler  Route handler used for the request.
 * @param \WP_REST_Request                                    $request  Request used to generate the response.
 */
function modify_rest_request( $response, array $handler, \WP_REST_Request $request ) {

	// Check are we on the products route.
	if ( 1 !== preg_match( '#/wc/v3/products/(?P<id>[\d]+)#', $request->get_route() ) ) {
		return $response;
	}

	// TODO: Check $_SERVER or $_REQUEST headers to see is it printify making the request.

	// TODO: Create an hourly cron job to update the exchange rate.
	$exchange_rate = 1.35;

	if ( $request->has_param( 'regular_price' ) ) {
		$new_price_usd = $request->get_param( 'regular_price' );
		$new_price_cad = $exchange_rate * $new_price_usd;
		$request->set_param( 'regular_price', $new_price_cad );
	}

	return $response;
}
add_filter( 'rest_request_before_callbacks', 'modify_rest_request', 10, 3 );