ping.php

<?php
/**
 * Anonymous PDF-download counter for /check-writer/
 *
 * Privacy contract:
 * - Does NOT read check fields, query strings, or request body.
 * - Does NOT set cookies or sessions.
 * - Stores only an integer total (+ optional daily totals).
 * - No IP logging in this file (rely on server access logs separately if needed).
 *
 * Read total: open count.json on the server, or GET this endpoint.
 */
declare(strict_types=1);

header('Content-Type: application/json; charset=utf-8');
header('Cache-Control: no-store');
header('X-Content-Type-Options: nosniff');
// Explicit: no cookies
header_remove('Set-Cookie');

// Only allow GET (read) and POST (increment). No other methods.
$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
if ($method !== 'GET' && $method !== 'POST') {
    http_response_code(405);
    echo json_encode(['ok' => false, 'error' => 'method_not_allowed']);
    exit;
}

$file = __DIR__ . '/count.json';

/**
 * @return array{total:int, by_day:array<string,int>}
 */
function load_counts(string $file): array
{
    $default = ['total' => 0, 'by_day' => []];
    if (!is_file($file)) {
        return $default;
    }
    $raw = file_get_contents($file);
    if ($raw === false || $raw === '') {
        return $default;
    }
    $data = json_decode($raw, true);
    if (!is_array($data)) {
        return $default;
    }
    return [
        'total' => (int) ($data['total'] ?? 0),
        'by_day' => is_array($data['by_day'] ?? null) ? $data['by_day'] : [],
    ];
}

/**
 * @param array{total:int, by_day:array<string,int>} $data
 */
function save_counts(string $file, array $data): bool
{
    $json = json_encode($data, JSON_PRETTY_PRINT);
    if ($json === false) {
        return false;
    }
    return file_put_contents($file, $json, LOCK_EX) !== false;
}

$counts = load_counts($file);

if ($method === 'POST') {
    // Increment only — never accept or store payload fields
    $counts['total']++;
    $day = gmdate('Y-m-d');
    $counts['by_day'][$day] = (int) ($counts['by_day'][$day] ?? 0) + 1;

    // Keep by_day from growing forever (last 90 days)
    if (count($counts['by_day']) > 90) {
        ksort($counts['by_day']);
        $counts['by_day'] = array_slice($counts['by_day'], -90, null, true);
    }

    if (!save_counts($file, $counts)) {
        http_response_code(500);
        echo json_encode(['ok' => false, 'error' => 'write_failed']);
        exit;
    }
}

echo json_encode([
    'ok' => true,
    'total' => $counts['total'],
    // today only — enough for a dashboard peek without dumping history
    'today' => (int) ($counts['by_day'][gmdate('Y-m-d')] ?? 0),
]);