yf_multi_accounts class

    public function _check($target_user_id = 0, $source_user_id = 0)
    {
        if (empty($source_user_id) && ! empty(main()->USER_ID)) {
            $source_user_id = main()->USER_ID;
        }
        if (empty($target_user_id) || empty($source_user_id)) {
            return false;
        }
        // Check if we need to do something here
        if (empty($this->CHECK_COOKIE_MATCH) && empty($this->CHECK_MULTI_IPS)) {
            return false;
        }
        $MULTI_ACCOUNT_FOUND = false;
        $users_ids = [
            $source_user_id => $source_user_id,
            $target_user_id => $target_user_id,
        ];
        // Try to get multi-accounts infos
        $Q = db()->query(
            'SELECT user_id, ip_match, cookie_match, matching_users 
			FROM ' . db('check_multi_accounts') . ' 
			WHERE user_id IN(' . implode(',', $users_ids) . ')'
            // Here we check fast if more detailed investigation needed
            . (" AND (ip_match = '1' OR cookie_match = '1') ")
        );
        $multi_infos = [];
        while ($A = db()->fetch_assoc($Q)) {
            $multi_infos[$A['user_id']] = $A;
        }
        $voter_info = $multi_infos[$source_user_id];
        $target_info = $multi_infos[$target_user_id];
        unset($multi_infos);
        // Try to find cookie match between target and voter
        if ($this->CHECK_COOKIE_MATCH) {
            if ( ! empty($voter_info) && ! empty($voter_info['matching_users'])
                && in_array($target_user_id, explode(',', $voter_info['matching_users']))
            ) {
                $MULTI_ACCOUNT_FOUND = true;
            }
            if ( ! empty($target_info) && ! empty($target_info['matching_users'])
                && in_array($source_user_id, explode(',', $target_info['matching_users']))
            ) {
                $MULTI_ACCOUNT_FOUND = true;
            }
        }
        // Try to find IPs match between target and voter
        if ($this->CHECK_MULTI_IPS && ! $MULTI_ACCOUNT_FOUND
            && ($voter_info['ip_match'] || $target_info['ip_match'])
        ) {
            $Q = db()->query(
                'SELECT 
					COUNT(DISTINCT(ip)) AS multi_ips
					, user_id
					, CAST(GROUP_CONCAT(DISTINCT ip ORDER BY ip ASC) AS CHAR) AS ips_list
				FROM ' . db('log_auth') . ' 
				WHERE user_id IN (' . implode(',', $users_ids) . ') 
					' . ($this->MULTI_IP_TTL ? ' AND date >= ' . (int) (time() - $this->MULTI_IP_TTL * 86400) : '') . '
				GROUP BY user_id 
				HAVING multi_ips > 1 
				ORDER BY multi_ips DESC'
            );
            $last_multi_ips = [];
            while ($A = db()->fetch_assoc($Q)) {
                $last_multi_ips[$A['user_id']] = explode(',', $A['ips_list']);
            }
            // Try to find same IPs
            if (array_intersect(
                (array) $last_multi_ips[$source_user_id],
                (array) $last_multi_ips[$target_user_id]
            )
            ) {
                $MULTI_ACCOUNT_FOUND = true;
            }
        }
        return $MULTI_ACCOUNT_FOUND;
    }