<?php

function request($url, $postfields = []) {
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    if(!empty($postfields)) {
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($postfields));
    }
    $json = curl_exec($ch);
    curl_close($ch);
    return json_decode($json, true);
}
function vkapi($m, $p = [], $o = false) {
    if(!isset($p['access_token'])) $p['access_token'] = '';
    if(!isset($p['v'])) $p['v'] = '5.95';

    return request("https://api.vk.com/method/{$m}", $p);
}

$lp = vkapi('groups.getLongPollServer', ['group_id' => 0])['response'];
$server = $lp['server'];
$key = $lp['key'];

$baseurl = "{$server}?act=a_check&key={$key}&wait=25&mode=2&ts=%d";
$url = sprintf($baseurl, $lp['ts']);

while(true) {
    $result = request($url);

    if(!is_null($result)) {
        if(isset($result['ts'])) {
            if(isset($result['updates']) && !empty($result['updates'])) {
                $url = sprintf($baseurl, $result['ts']);
                $updates = $result['updates'];

                foreach($updates as $key => $u) {
                    if($u['type'] != 'message_new') continue;
                    echo "Получено сообщение\n";
                }
            } else {
                $url = sprintf($baseurl, $result['ts']);
            }
        } elseif(isset($result['failed'])) {
            echo "failed ({$result['failed']})\n";

            switch($result['failed']) {
                case 1:
                    $url = sprintf($baseurl, $result['ts']);
                    break;

                case 2: case 3:
                    $lp = vkapi('groups.getLongPollServer', ['group_id' => 0])['response'];
                    $server = $lp['server'];
                    $key = $lp['key'];

                    $baseurl = "{$server}?act=a_check&key={$key}&wait=25&mode=2&ts=%d";
                    $url = sprintf($baseurl, $lp['ts']);
                    break;

                default: break;
            }
        } else {
            echo json_encode($result, JSON_UNESCAPED_UNICODE)."\n";
        }
    }
}