function sendPushNotification($user_id, $title, $body, $data = []) {
    global $pdo;
    
    // Get user's device token
    $stmt = $pdo->prepare("SELECT device_token FROM device_tokens WHERE user_id = ?");
    $stmt->execute([$user_id]);
    $device_token = $stmt->fetchColumn();
    
    if (!$device_token) {
        return false;
    }
    
    $notification = [
        'aps' => [
            'alert' => [
                'title' => $title,
                'body' => $body
            ],
            'sound' => 'default'
        ]
    ];
    
    // Add custom data
    if (!empty($data)) {
        $notification['data'] = $data;
    }
    
    // Your APNs configuration
    $apns_key = 'ios_app/AuthKey_GU2P6JS8K6.p8';
    $key_id = 'GU2P6JS8K6';
    $team_id = '78SS82JP67';
    $bundle_id = 'sss.SlipShareV5';
    
    // Send to APNs
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://api.push.apple.com/3/device/$device_token");
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($notification));
    curl_setopt($ch, CURLOPT_HTTPHEADER, [
        "Authorization: bearer " . generateJWT($team_id, $key_id, $apns_key),
        "apns-topic: $bundle_id",
        "apns-push-type: alert"
    ]);
    
    $response = curl_exec($ch);
    $http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    curl_close($ch);
    
    return $http_code == 200;
}