Magento – How to Override Messages on Product Page

I'm trying to override the messages block in the magento product page [and every other page actually] I'm trying to extend [and override] the default messages class. So far I have this:

in /app/etc/modules/Bbs_Messages.xml:

<?xml version="1.0"?>
<config>
    <modules>
        <Bbs_Messages>
            <active>true</active>
            <codePool>local</codePool>
        </Bbs_Messages>
    </modules>
</config>

in /app/code/local/Bbs/Messages/Core/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Bbs_Messages>
            <version>0.1.0</version>
        </Bbs_Messages>
    </modules>
    <global>
        <blocks>
            <core>
                <rewrite>
                    <messages>Bbs_Messages_Block_Messages</messages>
                </rewrite>
            </core>
        </blocks>
    </global>
</config>

in /app/code/local/Bbs/Messages/Block/Messages.php

<?php
class Bbs_Messages_Block_Messagesextends Mage_Core_Block_Messages
{
    public function getGroupedHtml()
    {
        return '<div data-alert class="alert-box"></div>';
    }
}

Then calling it in my view.phtml normally:

<?php echo $this->getMessagesBlock()->getGroupedHtml() ?>

All I'm getting is an error:

Fatal error: Call to a member function addMessages() on a non-object in /var/www/vhosts/bigblockstudios.ca/subdomains/autokraft/httpdocs/app/code/core/Mage/Core/Controller/Varien/Action.php on line 644

what did I miss here?

Updated:

Update as per RS's answer & corrected the above & added code to help anyone else who happens along with the same problem.

Didn't want to change it that much, so I left the local.xml override options intact [in case someone else ISN'T using Foundation]:

<reference name="root">

            <block type="core/messages" name="global_messages" as="global_messages">
                <action method="setMessagesFirstLevelTagName"><tagName>div</tagName></action>
                <action method="setMessagesSecondLevelTagName"><tagName>span</tagName></action>
            </block>

            <block type="core/messages" name="messages" as="messages">
                <action method="setMessagesFirstLevelTagName"><tagName>div</tagName></action>
                <action method="setMessagesSecondLevelTagName"><tagName>span</tagName></action>
            </block>

        </reference>

Updated /app/code/local/Bbs/Messages/Block/Messages.php with almost exactly the origainl function:

<?php
class Bbs_Messages_Block_Messages  extends Mage_Core_Block_Messages
{

    public function getCustomMessages($wrap_start,$wrap_end)
    {
        $types = array(
            Mage_Core_Model_Message::ERROR,
            Mage_Core_Model_Message::WARNING,
            Mage_Core_Model_Message::NOTICE,
            Mage_Core_Model_Message::SUCCESS
        );
        foreach ($types as $type) {

            // remap types for foundation output
            $_types = array(
                'success' => 'success',
                'notice' => 'info',
                'warning' => 'warning',
                'error' => 'alert',
            );

            if ( $messages = $this->getMessages($type) ) {

                if ( !$html ) {
                    $html .= '<' . $this->_messagesFirstLevelTagName . ' data-alert class="alert-box '.$_types[$type].'">';
                }

                $html .= '<' . $this->_messagesSecondLevelTagName . ' class="' . $_types[$type] . '-msg">';
                $html .= '<' . $this->_messagesFirstLevelTagName . '>';

                foreach ( $messages as $message ) {
                    $html.= '<' . $this->_messagesSecondLevelTagName . '>';
                    $html.= '<' . $this->_messagesContentWrapperTagName . '>';
                    $html.= ($this->_escapeMessageFlag) ? $this->escapeHtml($message->getText()) : $message->getText();
                    $html.= '</' . $this->_messagesContentWrapperTagName . '>';
                    $html.= '</' . $this->_messagesSecondLevelTagName . '>';
                }
                $html .= '</' . $this->_messagesFirstLevelTagName . '>';
                $html .= '</' . $this->_messagesSecondLevelTagName . '>';
            }
        }

        if ( $html) {
            $html .= '</' . $this->_messagesFirstLevelTagName . '>';

            // wrap it with our custom html
            $html = $wrap_start.$html.$wrap_end;
        }

        return $html;
    }


}

This way, the default magento messages are still available & I can get the custom ones by invoking the getCustomMessages function instead. All that needs to be done is to customize the html output of the above function….