<?php

$page_set = false;
if(isset($_GET['page'])) {
    $page = $_GET['page'];
    page_set = true;
}

$gallery_set = false;
if(isset($_GET['gallery'])) {
    $gallery = $_GET['gallery'];
    $gallery_set = true;
}

include("header.php");

if($page_set) {
    switch($page) {
        case "gallery":
            $gallery_path = "/path/to/galleries/{$gallery}.php";
            if($gallery_set && file_exists($gallery_path)) {
                include($gallery_path);
            } else {
                // include default gallery here
            }
        break;
        default:
            $page_path = "/path/to/pages/{$page}.php";
            if(file_exists($page_set)) {
                include($page_path);
            } else {
                // include home content here
            }
        break;
    }
} else {
    // include home content here
}

include("footer.php");

?>