functions.php

<?php if(!defined('IN_GS')){ die('you cannot load this page directly.'); }

// Function call if the condition matches.
if(function_exists('imanager') && return_page_slug() == 'basic') {  
    photobox();
}

/**
 * The function retrieves the markup 
 * It contains variables like [[URL]], [[CONTENT]] etc, 
 * which are replaced with values.
 * 
 * @var string $name - Template name to be returned
 * @return string
 */
function getTemplate($name)
{
    $tpls = array
    (
        'headerRes' => '<link href="[[URL]]" rel="stylesheet" type="text/css">',

        'script' => '<script src="[[URL]]"></script>',

        'galleryWrapper' => '<div id="gallery" class="box-thumb">[[CONTENT]]</div>',

        'galleryItem' => '<a href="[[URL]]"><img src="[[SRC]]" width="[[WIDTH]]" title="[[TITLE]]"></a>'
    );

    return isset($tpls[$name]) ? $tpls[$name] : $name;
}

/**
 * Takes care of creating the thumbnails.
 */
function getResizedUrl($url, $width = 200, $height = 0, $type = 'adaptiveResize')
{
    if(!file_exists(GSROOTPATH.$url)) return;
    $relpath = dirname($url);
    $path = dirname(GSROOTPATH.$url);
    $base = basename(GSROOTPATH.$url);
    if(!file_exists($path.'/thumbnail/'.$width.'x'.$height.'_'.$base)) {
        $thumb = \PhpThumbFactory::create(GSROOTPATH.$url);
        $path_parts = pathinfo(GSROOTPATH.$url);
        $thumb->{$type}($width, $height);
        $thumb->save($path.'/thumbnail/'.$width.'x'.$height.'_'.$base, $path_parts['extension']);
    }
    return IM_SITE_URL.$relpath.'/thumbnail/'.$width.'x'.$height.'_'.$base;
}

/**
 * Handling the PhotoBox logic.
 */
function photobox() 
{
    $imanager = imanager();
    include_once GSPLUGINPATH.'imanager/phpthumb/ThumbLib.inc.php';

    $templateParser = $imanager->getTemplateEngine();
    $itemMapper = $imanager->getItemMapper();
    $itemMapper->alloc(8);

    $photobox_scripts = $itemMapper->getSimpleItem('name=photobox-scripts');
    $photobox_images = $itemMapper->getSimpleItem('name=photobox-images');

    $header = '';
    $content = '';
    $images = '';
    $footer = '';

    if(isset($photobox_scripts->files)) {
        foreach($photobox_scripts->files as $file) {
            // it's an css file?
            if(substr($file, -3) == 'css') {
                $header .= $templateParser->render(getTemplate('headerRes'), array(
                    'URL' => IM_SITE_URL.$file
                ));
            }
            // it's js resource?
            if(substr($file, -2) == 'js') {
                $footer .= $templateParser->render(getTemplate('script'), array(
                    'URL' => IM_SITE_URL.$file
                )); 
            }
        }
    }

    if(isset($photobox_images->files)) {
        foreach($photobox_images->files as $key => $image) {
            if(in_array(substr($image, -3), array('jpg', 'peg', 'png'))) {

                $thumb = getResizedUrl($image, 200, 200);

                $images .= $templateParser->render(getTemplate('galleryItem'), array(
                    'URL' => IM_SITE_URL.$image,
                    'SRC' => $thumb,
                    'WIDTH' => 200,
                    'TITLE' => $photobox_images->files_title[$key]
                )); 
            }
        }

        $content = $templateParser->render(getTemplate('galleryWrapper'), array(
            'CONTENT' => $images
        ));
    }

    // Add your CSS to the theme header
    add_action('theme-header', function() use ($header) {
        echo $header;
    });

    // Add your scripts to the theme footer
    add_action('theme-footer', function() use ($footer) {
        echo $footer;
    });

    // content-top
    add_action('content-top', function() use ($content) {
        echo $content;
    });
}