parent::initProcess();

if (Tools::isSubmit('submitMessage'))
{
    $customer = new Customer(Tools::getValue('id_customer'));
    if (!Validate::isLoadedObject($customer)) {
        $this->errors[] = Tools::displayError('The customer is invalid.');
    } elseif (!Tools::getValue('message')) {
        $this->errors[] = Tools::displayError('The message cannot be blank.');
    } else {
        $rules = call_user_func(array('Message', 'getValidationRules'), 'Message');
        foreach ($rules['required'] as $field) {
            if (($value = Tools::getValue($field)) == false && (string)$value != '0') {
                if (!Tools::getValue('id_'.$this->table) || $field != 'passwd') {
                    $this->errors[] = sprintf(Tools::displayError('field %s is required.'), $field);
                }
            }
        }
        foreach ($rules['size'] as $field => $maxLength) {
            if (Tools::getValue($field) && Tools::strlen(Tools::getValue($field)) > $maxLength) {
                $this->errors[] = sprintf(Tools::displayError('field %1$s is too long (%2$d chars max).'), $field, $maxLength);
            }
        }
        foreach ($rules['validate'] as $field => $function) {
            if (Tools::getValue($field)) {
                if (!Validate::$function(htmlentities(Tools::getValue($field), ENT_COMPAT, 'UTF-8'))) {
                    $this->errors[] = sprintf(Tools::displayError('field %s is invalid.'), $field);
                }
            }
        }
        

        if (!count($this->errors))
        {
            $customer_message = new CustomerMessage();
            $customer_message->id_customer_thread = $customer_thread->id;
            $customer_message->id_employee = (int)$this->context->employee->id;
            $customer_message->message = Tools::getValue('message');
            $customer_message->private = Tools::getValue('visibility');

            if (!$customer_message->add()) {
                $this->errors[] = Tools::displayError('An error occurred while saving the message.');
            } else {
                $message = $customer_message->message;
                if (Configuration::get('PS_MAIL_TYPE', null, null, $order->id_shop) != Mail::TYPE_TEXT) {
                    $message = Tools::nl2br($customer_message->message);
                }

                $varsTpl = array(
                    '{lastname}' => $customer->lastname,
                    '{firstname}' => $customer->firstname,
                    '{order_name}' => 'NO',
                    '{message}' => $message
                );
                if (@Mail::Send($customer->id_lang, 'order_merchant_comment',
                    Mail::l('New message regarding your order', (int)$customer->id_lang), $varsTpl, $customer->email,
                    $customer->firstname.' '.$customer->lastname, null, null, null, null, _PS_MAIL_DIR_, true, (int)$customer->id_shop)) {
                    Tools::redirectAdmin(self::$currentIndex.'&id_customer='.$customer->id.'&viewcustomer&conf=11'.'&token='.$this->token);
                }
            }
            $this->errors[] = Tools::displayError('An error occurred while sending an email to the customer.');
        }
    }
}

/адм.дир/themes/default/template/controllers/customers/helpers/view/view.tpl

<div class="panel">
    <div class="panel-heading">
        <i class="icon-eye-close"></i> {l s='Add a private note'}
    </div>
    <div class="alert alert-info">{l s='This note will be displayed to all employees but not to customers.'}</div>
    <form id="customer_note" class="form-horizontal" action="ajax.php" method="post" onsubmit="saveCustomerNote({$customer->id|intval});return false;" >
        <div class="form-group">
            <div class="col-lg-12">
                <textarea name="note" id="noteContent" onkeyup="$('#submitCustomerNote').removeAttr('disabled');">{$customer_note}</textarea>
            </div>
        </div>
        <div class="row">
            <div class="col-lg-12">
                <button type="submit" id="submitCustomerNote" class="btn btn-default pull-right" disabled="disabled">
                    <i class="icon-save"></i>
                    {l s='Save'}
                </button>
            </div>
        </div>
        <span id="note_feedback"></span>
    </form>
</div>

<div id="messages" class="well hidden-print">
    <form action="{$smarty.server.REQUEST_URI|escape:'html':'UTF-8'}" method="post">
        <div id="message" class="form-horizontal">
            <div class="form-group">
                <label class="control-label col-lg-3">{l s='Message'}</label>
                <div class="col-lg-9">
                    <textarea id="txt_msg" class="textarea-autosize" name="message">{Tools::getValue('message')|escape:'html':'UTF-8'}</textarea>
                    <p id="nbchars"></p>
                </div>
            </div>

            <input type="hidden" name="id_customer" value="{$customer->id|intval}" />
            <button type="submit" id="submitMessage" class="btn btn-primary pull-right" name="submitMessage">
                {l s='Send message'}
            </button>
            <div class="clearfix"></div>
        </div>
    </form>
</div>