SB PHP Menu Builder: Create menus and store definitions in files

    The SB Menu class is a PHP class that allows for the creation, modification, saving, loading, and display of a menu tree without the need for a database. This class is designed to be simple, efficient, and easily customizable. It uses a flatfile approach, meaning that the menu structure is stored in a text file rather than a database.
    'label' (user provided) and 'id' (generated) are default fields in the base class.

Class Methods:
    save($filename) - saves the menu tree to a file
    load($filename) - loads the menu tree from a file

    getNodeByField($field, $value) - returns a reference to the node with a field that matches a value
    applyCallbackToNode($id, $callback) - applies a callback to a node with a specific id
    applyCallbackToNodeByField($field, $value, $callback) - applies a callback to a node with a specific field that matches a value

Examples:
	class.sb_menu.test.directory.php 	// an example showing a directory and subdirectories
	class.sb_menu.test.simple.php		// a simple multilevel collapsible flexible and responsive accordion menu


EXAMPLE USAGE:
EXAMPLE USAGE:
EXAMPLE USAGE:

<?php
    // include the class
    include_once("class.sb_menu_1.0.php");

    // example creation... (look at class.sb_menu.test.simple.php for extended class needed to render)
    class SimpleTree_Extended extends Tree { ... extended code ( render(), renderNode(), etc ) ... }

    // create extended class of Tree and throw in a render and renderNode to customize display based on dynamic data fields
    // we pass the name we want for the main root node. In the example, we skip rendering this root node.
    $menu = new SimpleTree_Extended(new TreeNode('Main Menu')); // .. or the extended class to seperate the render() method


    // now add some menus...
            // when menu is created, a root node is created and assigned to $menu->root. This is our main level.
            $last_menu = $menu->root->addChild(new TreeNode('Submenu 1'));
            $last_menu = $menu->root->addChild(new TreeNode('Submenu 2'));
                // another level
                $next_level = $last_menu->addChild(new TreeNode('Item 2.1'));
                
                // example adding more data for our extended class to use with a custom render() method
                $next_level->data['url'] = "https://www.google.com";    // handled in extended class render
                $next_level->data['target'] = "_blank";                 // handled in extended class render

    // # use a callback to run some code on a specific node via its id (id and label are default fields in base class)
    $menu->applyCallbackToNode($s2_id, function($node) {
        $node->data['label'] = 'New Label';
        $new_submenu = new TreeNode('New Submenu');
        $node->addChild($new_submenu);
    });


    // example usage of applyCallbackToNodeByField($field, $value, $callback) 
    // (this example changes the label of the node with label 'Submenu 1' to 'New Label')
    $menu->applyCallbackToNodeByField('label', 'Submenu 1', function($node) {
        $node->data['label'] = 'New Label';
    });


    // get the reference to the node by a field for modification. (only returns first match)
    // example usage of getNodeByField($key, $value)
    $s2 = $menu->getNodeByField('label', 'Submenu 2');
    $s2_id = $s2->data['id'];


    # save (ez) (make sure directory or file is writeable)
    $menu->save('menu-simple.txt');

    # load (pz)
    $menu2 = $menu->load('menu-simple.txt');


    // render (display the menu :: see example Tree extended class in class.sb_menu.test.simple.php )
    echo $menu->render('sbmenu'); // render defined in extended class
?>