<?php
/**
 * The payload of a t.me/{bot}?start={payload} link. Telegram allows up to 64 of A-Z a-z 0-9 _ -.
 *
 * - Customer:  "o{order id in base 36}_{16-char MAC}" — the MAC covers the order id AND the
 *   order key, so a guessed order number is not enough to subscribe to someone else's order.
 * - Shop owner: "a{24 random chars}" — a one-time invite created on the settings page, valid
 *   for one hour; only its hash is stored.
 *
 * @package Orderchirp
 */

namespace Orderchirp;

defined( 'ABSPATH' ) || exit;

final class Link_Token {

	const MAC_LENGTH = 16;

	/**
	 * Customer link payload for an order.
	 *
	 * @param int    $order_id  Order id.
	 * @param string $order_key Order key (wc_order_...).
	 * @param string $secret    Site secret.
	 * @return string
	 */
	public static function for_order( $order_id, $order_key, $secret ) {
		return 'o' . base_convert( (string) (int) $order_id, 10, 36 ) . '_' . self::mac( (int) $order_id, (string) $order_key, $secret );
	}

	/**
	 * Read a payload without trusting it.
	 *
	 * @param string $payload Payload from /start.
	 * @return array{type:string,order_id?:int,mac?:string,code?:string}|null Null when malformed.
	 */
	public static function parse( $payload ) {
		$payload = (string) $payload;
		if ( strlen( $payload ) > 64 || 1 !== preg_match( '/^[A-Za-z0-9_-]+$/D', $payload ) ) {
			return null;
		}
		if ( 1 === preg_match( '/^o([0-9a-z]{1,12})_([A-Za-z0-9_-]{' . self::MAC_LENGTH . '})$/D', $payload, $m ) ) {
			$id = (int) base_convert( $m[1], 36, 10 );
			return $id > 0 ? array( 'type' => 'order', 'order_id' => $id, 'mac' => $m[2] ) : null;
		}
		if ( 1 === preg_match( '/^a([A-Za-z0-9]{24})$/D', $payload, $m ) ) {
			return array( 'type' => 'owner', 'code' => $m[1] );
		}
		return null;
	}

	/**
	 * Constant-time check of a customer payload against the order's key.
	 *
	 * @param int    $order_id  Order id.
	 * @param string $order_key Order key.
	 * @param string $mac       MAC from the payload.
	 * @param string $secret    Site secret.
	 * @return bool
	 */
	public static function verify_order( $order_id, $order_key, $mac, $secret ) {
		if ( '' === (string) $order_key ) {
			return false;
		}
		return hash_equals( self::mac( (int) $order_id, (string) $order_key, $secret ), (string) $mac );
	}

	/**
	 * MAC: HMAC-SHA256 over "order|{id}|{key}", base64url, first 16 characters (96 bits).
	 *
	 * @param int    $order_id  Order id.
	 * @param string $order_key Order key.
	 * @param string $secret    Site secret.
	 * @return string
	 */
	private static function mac( $order_id, $order_key, $secret ) {
		$raw = hash_hmac( 'sha256', 'order|' . $order_id . '|' . $order_key, $secret, true );
		// phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode -- URL-safe token, not obfuscation.
		return substr( rtrim( strtr( base64_encode( $raw ), '+/', '-_' ), '=' ), 0, self::MAC_LENGTH );
	}

	/**
	 * A new owner invite code (24 alphanumerics).
	 *
	 * @return string
	 */
	public static function new_owner_code() {
		$alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
		$code     = '';
		for ( $i = 0; $i < 24; $i++ ) {
			$code .= $alphabet[ random_int( 0, strlen( $alphabet ) - 1 ) ];
		}
		return $code;
	}
}