<?php
/**
 * AI answer-engine visibility log for the static site (2026-08-27).
 *
 * Reached ONLY through the .htaccess rewrite: requests for "/" or "/*.html" whose
 * User-Agent is an AI crawler/fetcher, or whose Referer is an AI assistant.
 * Appends one line to ../ai-hits/ai-hits-YYYY-MM-DD.tsv (outside the web root),
 * then serves the requested HTML file unchanged (same status, same body).
 * Never edit page HTML here — this is a passthrough.
 */
const AI_CRAWLER_RE = '/(GPTBot|OAI-SearchBot|ChatGPT-User|ClaudeBot|Claude-Web|Claude-User|Claude-SearchBot|anthropic-ai|PerplexityBot|Perplexity-User|Google-Extended|Meta-ExternalAgent|Meta-ExternalFetcher|Amazonbot|Applebot-Extended|DuckAssistBot|Bytespider|CCBot|cohere-ai|YouBot|Diffbot|MistralAI-User)/i';

$root = __DIR__;
$req  = parse_url($_SERVER['REQUEST_URI'] ?? '/', PHP_URL_PATH) ?: '/';
$file = ($req === '/') ? 'index.html' : ltrim($req, '/');
$real = realpath($root . '/' . $file);
$ok   = $real && str_starts_with($real, $root . '/') && str_ends_with($real, '.html') && is_file($real)
        && basename($real) !== 'ai-log.php';

$ua  = $_SERVER['HTTP_USER_AGENT'] ?? '';
$ref = $_SERVER['HTTP_REFERER'] ?? '';
$agent = preg_match(AI_CRAWLER_RE, $ua, $m) ? $m[1] : '';
$kind  = $agent ? 'crawler' : 'referral';
$who   = $agent ?: (string)(parse_url($ref, PHP_URL_HOST) ?: '');
$clean = static fn($f) => str_replace(["\t", "\n", "\r"], ' ', (string)$f);
$dir = dirname($root) . '/ai-hits';
if (!is_dir($dir)) @mkdir($dir, 0755, true);
$day = (new DateTimeImmutable('now', new DateTimeZone('America/Chicago')))->format('Y-m-d');
@file_put_contents($dir . '/ai-hits-' . $day . '.tsv',
    implode("\t", array_map($clean, [gmdate('c'), $kind, $who, $req, $ref, substr($ua, 0, 200)])) . "\n",
    FILE_APPEND | LOCK_EX);

if (!$ok) {
    http_response_code(404);
    if (is_file($root . '/404.html')) readfile($root . '/404.html');
    exit;
}
header('Content-Type: text/html; charset=utf-8');
readfile($real);