<?php
namespace Relay\Remote;

use Relay\Support\RelayError;

/**
 * Body of every site-to-site request and response: gzip( JSON line "\n" payload ). One binary format for
 * metadata and SQL alike: a request sends it as application/octet-stream, an answer inside JSON (Transport).
 */
final class Frame
{
    public const MAX_DECODED = 67108864;

    public static function encode(array $meta, string $payload = ''): string
    {
        return (string) gzencode(json_encode($meta, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . "\n" . $payload, 6);
    }

    /** @return array{meta: array, payload: string} */
    public static function decode(string $body, int $max = self::MAX_DECODED): array
    {
        $raw = $body === '' ? false : @gzdecode($body, $max); // Damaged data makes PHP warn as well as return false; false is handled here, and PHP has no way to try it without the warning.
        if (!is_string($raw)) {
            throw new RelayError('remote.bad_frame', esc_html__('The other site sent data SiteRelay could not read.', 'siterelay'));
        }
        $at = strpos($raw, "\n");
        $meta = json_decode($at === false ? $raw : substr($raw, 0, $at), true);
        if (!is_array($meta)) {
            throw new RelayError('remote.bad_frame', esc_html__('The other site sent data SiteRelay could not read.', 'siterelay'));
        }
        return ['meta' => $meta, 'payload' => $at === false ? '' : (string) substr($raw, $at + 1)];
    }
}