<?php
declare(strict_types=1);

const MERCURE_KEY = '!ChangeThisDevKey!';
const MERCURE_HUB = 'http://127.0.0.1:8765/.well-known/mercure';
const MERCURE_TOPIC = 'app://ping';

$path = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH);
$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';

header('Access-Control-Allow-Origin: *');

if ($path === '/api/ping' && $method === 'GET') {
    $payload = ['pong' => true, 'now' => date('c')];
    publishToMercure(MERCURE_TOPIC, $payload);
    header('Content-Type: application/json');
    echo json_encode($payload);
    return;
}

http_response_code(404);
header('Content-Type: application/json');
echo json_encode(['error' => 'not found', 'path' => $path]);

function publishToMercure(string $topic, array $data): void
{
    $body = http_build_query([
        'topic' => $topic,
        'data'  => json_encode($data),
    ]);

    $ch = curl_init(MERCURE_HUB);
    curl_setopt_array($ch, [
        CURLOPT_POST           => true,
        CURLOPT_POSTFIELDS     => $body,
        CURLOPT_HTTPHEADER     => [
            'Content-Type: application/x-www-form-urlencoded',
            'Authorization: Bearer ' . mintPublisherJwt(),
        ],
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_TIMEOUT        => 5,
    ]);
    $resp = curl_exec($ch);
    $code = curl_getinfo($ch, CURLINFO_HTTP_CODE);

    error_log("mercure publish topic=$topic http=$code body=" . ($resp === false ? 'false' : (string) $resp));
}

function mintPublisherJwt(): string
{
    $header  = ['alg' => 'HS256', 'typ' => 'JWT'];
    $payload = ['mercure' => ['publish' => ['*']]];

    $h = b64url(json_encode($header));
    $p = b64url(json_encode($payload));
    $s = b64url(hash_hmac('sha256', "$h.$p", MERCURE_KEY, true));

    return "$h.$p.$s";
}

function b64url(string $bytes): string
{
    return rtrim(strtr(base64_encode($bytes), '+/', '-_'), '=');
}