<?php
/**
 * Tile-Proxy mit Disk-Cache — DSGVO-sicherer Ersatz für direkte
 * Browser-Requests an OSM/CARTO-Tile-Server.
 *
 * Flow:
 *   Browser → tile-proxy.php (euer Server) → [Cache-Hit? ja: raus]
 *                                          → [Cache-Miss? Upstream holen, cachen, raus]
 *
 * Aufruf: /tile-proxy?z={z}&x={x}&y={y}&p={osm|carto}
 *
 * Konfiguration über .env:
 *   TILE_CACHE_DIR=/absoluter/pfad/zum/cache/   (optional;
 *     Default: APP_ROOT/data/tiles/)
 */
require_once __DIR__ . '/config/app.php';

// ============================================================
// Whitelist — was darf rein, was raus
// ============================================================
const PROVIDERS = [
    'osm' => [
        'label'       => 'OpenStreetMap',
        'url_pattern' => 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
        'max_zoom'    => 18,
    ],
    'osm-de' => [
        'label'       => 'OpenStreetMap Deutsch (FOSSGIS e.V.)',
        'url_pattern' => 'https://tile.openstreetmap.de/{z}/{x}/{y}.png',
        'max_zoom'    => 18,
    ],
    'carto' => [
        'label'       => 'CARTO Positron',
        'url_pattern' => 'https://cartodb-basemaps-a.global.ssl.fastly.net/light_all/{z}/{x}/{y}.png',
        'max_zoom'    => 18,
    ],
];
const MIN_ZOOM  = 3;
const MAX_ZOOM  = 18;
const CACHE_TTL_DAYS = 30;   // Browser-Cache-Max-Age
const UPSTREAM_TIMEOUT = 10; // Sekunden

// ============================================================
// Parameter-Validierung
// ============================================================
$z = filter_input(INPUT_GET, 'z', FILTER_VALIDATE_INT, ['options' => ['min_range' => MIN_ZOOM, 'max_range' => MAX_ZOOM]]);
$x = filter_input(INPUT_GET, 'x', FILTER_VALIDATE_INT, ['options' => ['min_range' => 0, 'max_range' => 1 << MAX_ZOOM]]);
$y = filter_input(INPUT_GET, 'y', FILTER_VALIDATE_INT, ['options' => ['min_range' => 0, 'max_range' => 1 << MAX_ZOOM]]);
$p = filter_input(INPUT_GET, 'p', FILTER_CALLBACK, ['options' => fn($v) => is_string($v) && preg_match('/^[a-z][a-z0-9-]{0,15}$/', $v) ? $v : false]);

if ($z === null || $z === false || $x === false || $y === false || !$p || !isset(PROVIDERS[$p])) {
    http_response_code(400);
    header('Content-Type: text/plain; charset=utf-8');
    exit("Ungültige Parameter. Erwartet: ?z=INT&x=INT&y=INT&p=osm|carto\n");
}

$xMax = (1 << $z) - 1;
if ($x < 0 || $x > $xMax || $y < 0 || $y > $xMax) {
    http_response_code(400);
    exit("Tile-Koordinaten außerhalb des Zoom-Bereichs.\n");
}

$providerConf = PROVIDERS[$p];
if ($z > $providerConf['max_zoom']) {
    http_response_code(400);
    exit("Zoom-Level {$z} wird von Provider {$p} nicht unterstützt.\n");
}

// ============================================================
// Cache-Pfad bestimmen
// ============================================================
$cacheDir = defined('TILE_CACHE_DIR')
    ? rtrim(TILE_CACHE_DIR, '/\\')
    : rtrim(APP_ROOT, '/\\') . '/data/tiles';

$tileDir  = $cacheDir . "/$p/$z/$x";
$tilePath = $tileDir . "/$y.png";

// ============================================================
// Cache-Hit: sofort ausliefern
// ============================================================
if (is_file($tilePath) && filesize($tilePath) > 0) {
    _serveTile($tilePath);
    exit;
}

// ============================================================
// Cache-Miss: upstream holen
// ============================================================
$upstreamUrl = strtr($providerConf['url_pattern'], [
    '{z}' => $z, '{x}' => $x, '{y}' => $y,
]);

$ctx = stream_context_create([
    'http' => [
        'method'     => 'GET',
        'timeout'    => UPSTREAM_TIMEOUT,
        'user_agent' => 'GeoGraSim/1.0 (+https://geograsim.at; educational tile cache)',
        'header'     => "Accept: image/png,image/*\r\n",
    ],
    'ssl' => [
        'verify_peer'      => true,
        'verify_peer_name' => true,
    ],
]);

$data = @file_get_contents($upstreamUrl, false, $ctx);

if ($data === false || strlen($data) < 100) {
    http_response_code(502);
    header('Content-Type: text/plain; charset=utf-8');
    exit("Upstream nicht erreichbar: {$providerConf['label']}\n");
}

// ============================================================
// In Cache schreiben (best-effort, Fehler ignorieren)
// ============================================================
if (!is_dir($tileDir)) {
    @mkdir($tileDir, 0775, true);
}
if (is_dir($tileDir) && is_writable($tileDir)) {
    @file_put_contents($tilePath, $data, LOCK_EX);
}

// ============================================================
// An Browser ausliefern
// ============================================================
header('Content-Type: image/png');
header('Cache-Control: public, max-age=' . (CACHE_TTL_DAYS * 86400) . ', immutable');
header('X-Tile-Cache: MISS');
echo $data;

// ============================================================
// Helper: Tile aus Cache servieren
// ============================================================
function _serveTile(string $path): void {
    $etag = '"' . md5_file($path) . '"';
    $mtime = filemtime($path);
    $lastMod = gmdate('D, d M Y H:i:s', $mtime) . ' GMT';

    header('Content-Type: image/png');
    header('Cache-Control: public, max-age=' . (CACHE_TTL_DAYS * 86400) . ', immutable');
    header('ETag: ' . $etag);
    header('Last-Modified: ' . $lastMod);
    header('X-Tile-Cache: HIT');

    $ifNoneMatch = $_SERVER['HTTP_IF_NONE_MATCH'] ?? '';
    $ifModSince  = $_SERVER['HTTP_IF_MODIFIED_SINCE'] ?? '';
    if ($ifNoneMatch === $etag || ($ifModSince && strtotime($ifModSince) >= $mtime)) {
        http_response_code(304);
        return;
    }

    header('Content-Length: ' . filesize($path));
    readfile($path);
}