<?php

namespace SilverStripe\Admin;

use SilverStripe\CMS\Controllers\CMSPageEditController;
use SilverStripe\CMS\Controllers\CMSPagesController;
use SilverStripe\CMS\Model\SiteTree;
use SilverStripe\CMS\Model\VirtualPage;
use SilverStripe\CMS\Controllers\SilverStripeNavigator;
use SilverStripe\Control\ContentNegotiator;
use SilverStripe\Control\Director;
use SilverStripe\Control\HTTPResponse;
use SilverStripe\Control\Session;
use SilverStripe\Control\HTTPRequest;
use SilverStripe\Control\HTTPResponse_Exception;
use SilverStripe\Control\Controller;
use SilverStripe\Control\PjaxResponseNegotiator;
use SilverStripe\Core\Convert;
use SilverStripe\Core\Config\Config;
use Psr\SimpleCache\CacheInterface;
use SilverStripe\Core\ClassInfo;
use SilverStripe\Core\Injector\Injector;
use SilverStripe\Dev\Deprecation;
use SilverStripe\Forms\Form;
use SilverStripe\Forms\HiddenField;
use SilverStripe\Forms\HTMLEditor\TinyMCEConfig;
use SilverStripe\Forms\LiteralField;
use SilverStripe\Forms\FormAction;
use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\DropdownField;
use SilverStripe\Forms\PrintableTransformation;
use SilverStripe\Forms\HTMLEditor\HTMLEditorConfig;
use SilverStripe\Forms\HTMLEditor\HTMLEditorField_Toolbar;
use SilverStripe\Forms\Schema\FormSchema;
use SilverStripe\i18n\i18n;
use SilverStripe\ORM\FieldType\DBHTMLText;
use SilverStripe\ORM\Hierarchy\Hierarchy;
use SilverStripe\ORM\SS_List;
use SilverStripe\ORM\ValidationResult;
use SilverStripe\ORM\Versioning\Versioned;
use SilverStripe\ORM\DataModel;
use SilverStripe\ORM\ValidationException;
use SilverStripe\ORM\ArrayList;
use SilverStripe\ORM\FieldType\DBField;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\DB;
use SilverStripe\Security\SecurityToken;
use SilverStripe\Security\Member;
use SilverStripe\Security\Permission;
use SilverStripe\Security\Security;
use SilverStripe\Security\PermissionProvider;
use SilverStripe\View\SSViewer;
use SilverStripe\View\Requirements;
use SilverStripe\View\ArrayData;
use ReflectionClass;
use InvalidArgumentException;

use SilverStripe\SiteConfig\SiteConfig;

/**
 * LeftAndMain is the parent class of all the two-pane views in the CMS.
 * If you are wanting to add more areas to the CMS, you can do it by subclassing LeftAndMain.
 *
 * This is essentially an abstract class which should be subclassed.
 * See {@link CMSMain} for a good example.
 */
class LeftAndMain extends Controller implements PermissionProvider
{

    /**
     * Form schema header identifier
     */
    const SCHEMA_HEADER = 'X-Formschema-Request';

    /**
     * Enable front-end debugging (increases verbosity) in dev mode.
     * Will be ignored in live environments.
     *
     * @var bool
     */
    private static $client_debugging = true;

    /**
     * The current url segment attached to the LeftAndMain instance
     *
     * @config
     * @var string
     */
    private static $url_segment = null;

    /**
     * @config
     * @var string Used by {@link AdminRootController} to augment Director route rules for sub-classes of LeftAndMain
     */
    private static $url_rule = '/$Action/$ID/$OtherID';

    /**
     * @config
     * @var string
     */
    private static $menu_title;

    /**
     * @config
     * @var string
     */
    private static $menu_icon;

    /**
     * @config
     * @var int
     */
    private static $menu_priority = 0;

    /**
     * @config
     * @var int
     */
    private static $url_priority = 50;

    /**
     * A subclass of {@link DataObject}.
     *
     * Determines what is managed in this interface, through
     * {@link getEditForm()} and other logic.
     *
     * @config
     * @var string
     */
    private static $tree_class = null;

    /**
     * The url used for the link in the Help tab in the backend
     *
     * @config
     * @var string
     */
    private static $help_link = '//userhelp.silverstripe.org/framework/en/3.5';

    /**
     * @var array
     */
    private static $allowed_actions = [
        'index',
        'save',
        'savetreenode',
        'getsubtree',
        'updatetreenodes',
        'printable',
        'show',
        'EditorToolbar',
        'EditForm',
        'AddForm',
        'batchactions',
        'BatchActionsForm',
        'schema',
    ];

    private static $url_handlers = [
        'GET schema/$FormName/$ItemID/$OtherItemID' => 'schema'
    ];

    private static $dependencies = [
        'FormSchema' => '%$FormSchema'
    ];

    /**
     * Current form schema helper
     *
     * @var FormSchema
     */
    protected $schema = null;

    /**
     * Assign themes to use for cms
     *
     * @config
     * @var array
     */
    private static $admin_themes = [
        'silverstripe/framework:/admin/themes/cms-forms',
        SSViewer::DEFAULT_THEME,
    ];

    /**
     * Codes which are required from the current user to view this controller.
     * If multiple codes are provided, all of them are required.
     * All CMS controllers require "CMS_ACCESS_LeftAndMain" as a baseline check,
     * and fall back to "CMS_ACCESS_<class>" if no permissions are defined here.
     * See {@link canView()} for more details on permission checks.
     *
     * @config
     * @var array
     */
    private static $required_permission_codes;

    /**
     * @config
     * @var String Namespace for session info, e.g. current record.
     * Defaults to the current class name, but can be amended to share a namespace in case
     * controllers are logically bundled together, and mainly separated
     * to achieve more flexible templating.
     */
    private static $session_namespace;

    /**
     * Register additional requirements through the {@link Requirements} class.
     * Used mainly to work around the missing "lazy loading" functionality
     * for getting css/javascript required after an ajax-call (e.g. loading the editform).
     *
     * YAML configuration example:
     * <code>
     * LeftAndMain:
     *   extra_requirements_javascript:
     *     - mysite/javascript/myscript.js
     * </code>
     *
     * @config
     * @var array
     */
    private static $extra_requirements_javascript = array();

    /**
     * YAML configuration example:
     * <code>
     * LeftAndMain:
     *   extra_requirements_css:
     *     - mysite/css/mystyle.css:
    *          media: screen
     * </code>
     *
     * @config
     * @var array See {@link extra_requirements_javascript}
     */
    private static $extra_requirements_css = array();

    /**
     * @config
     * @var array See {@link extra_requirements_javascript}
     */
    private static $extra_requirements_themedCss = array();

    /**
     * If true, call a keepalive ping every 5 minutes from the CMS interface,
     * to ensure that the session never dies.
     *
     * @config
     * @var boolean
     */
    private static $session_keepalive_ping = true;

    /**
     * Value of X-Frame-Options header
     *
     * @config
     * @var string
     */
    private static $frame_options = 'SAMEORIGIN';

    /**
     * @var PjaxResponseNegotiator
     */
    protected $responseNegotiator;

    /**
     * Gets the combined configuration of all LeafAndMain subclasses required by the client app.
     *
     * @return string
     *
     * WARNING: Experimental API
     */
    public function getCombinedClientConfig()
    {
        $combinedClientConfig = ['sections' => []];
        $cmsClassNames = CMSMenu::get_cms_classes('SilverStripe\\Admin\\LeftAndMain', true, CMSMenu::URL_PRIORITY);

        foreach ($cmsClassNames as $className) {
            $combinedClientConfig['sections'][$className] =  Injector::inst()->get($className)->getClientConfig();
        }

        // Pass in base url (absolute and relative)
        $combinedClientConfig['baseUrl'] = Director::baseURL();
        $combinedClientConfig['absoluteBaseUrl'] = Director::absoluteBaseURL();
        $combinedClientConfig['adminUrl'] = AdminRootController::admin_url();

        // Get "global" CSRF token for use in JavaScript
        $token = SecurityToken::inst();
        $combinedClientConfig[$token->getName()] = $token->getValue();

        // Set env
        $combinedClientConfig['environment'] = Director::get_environment_type();
        $combinedClientConfig['debugging'] = LeftAndMain::config()->uninherited('client_debugging');

        return Convert::raw2json($combinedClientConfig);
    }

    /**
     * Returns configuration required by the client app.
     *
     * @return array
     *
     * WARNING: Experimental API
     */
    public function getClientConfig()
    {
        return [
            // Trim leading/trailing slash to make it easier to concatenate URL
            // and use in routing definitions.
            'url' => trim($this->Link(), '/'),
        ];
    }

    /**
     * Get form schema helper
     *
     * @return FormSchema
     */
    public function getFormSchema()
    {
        return $this->schema;
    }

    /**
     * Set form schema helper for this controller
     *
     * @param FormSchema $schema
     * @return $this
     */
    public function setFormSchema(FormSchema $schema)
    {
        $this->schema = $schema;
        return $this;
    }

    /**
     * Gets a JSON schema representing the current edit form.
     *
     * WARNING: Experimental API.
     *
     * @param HTTPRequest $request
     * @return HTTPResponse
     */
    public function schema($request)
    {
        $formName = $request->param('FormName');
        $itemID = $request->param('ItemID');

        if (!$formName) {
            return (new HTTPResponse('Missing request params', 400));
        }

        $formMethod = "get{$formName}";
        if (!$this->hasMethod($formMethod)) {
            return (new HTTPResponse('Form not found', 404));
        }

        if (!$this->hasAction($formName)) {
            return (new HTTPResponse('Form not accessible', 401));
        }

        if ($itemID) {
            $form = $this->{$formMethod}($itemID);
        } else {
            $form = $this->{$formMethod}();
        }
        $schemaID = $request->getURL();
        return $this->getSchemaResponse($schemaID, $form);
    }

    /**
     * Check if the current request has a X-Formschema-Request header set.
     * Used by conditional logic that responds to validation results
     *
     * @return bool
     */
    protected function getSchemaRequested()
    {
        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
        return !empty($parts);
    }

    /**
     * Generate schema for the given form based on the X-Formschema-Request header value
     *
     * @param string $schemaID ID for this schema. Required.
     * @param Form $form Required for 'state' or 'schema' response
     * @param ValidationResult $errors Required for 'error' response
     * @param array $extraData Any extra data to be merged with the schema response
     * @return HTTPResponse
     */
    protected function getSchemaResponse($schemaID, $form = null, ValidationResult $errors = null, $extraData = [])
    {
        $parts = $this->getRequest()->getHeader(static::SCHEMA_HEADER);
        $data = $this
            ->getFormSchema()
            ->getMultipartSchema($parts, $schemaID, $form, $errors);

        if ($extraData) {
            $data = array_merge($data, $extraData);
        }

        $response = new HTTPResponse(Convert::raw2json($data));
        $response->addHeader('Content-Type', 'application/json');
        return $response;
    }

    /**
     * Get link to schema url for a given form
     *
     * @param Form $form
     * @return string
     */
    protected function getSchemaLinkForForm(Form $form)
    {
        $parts = [$this->Link('schema'), $form->getName()];
        if (($record = $form->getRecord()) && $record->isInDB()) {
            $parts[] = $record->ID;
        } elseif (($data = $form->getData()) && !empty($data['ID'])) {
            $parts[] = $data['ID'];
        }
        return Controller::join_links($parts);
    }

    /**
     * @param Member $member
     * @return boolean
     */
    public function canView($member = null)
    {
        if (!$member && $member !== false) {
            $member = Member::currentUser();
        }

        // cms menus only for logged-in members
        if (!$member) {
            return false;
        }

        // alternative extended checks
        if ($this->hasMethod('alternateAccessCheck')) {
            $alternateAllowed = $this->alternateAccessCheck();
            if ($alternateAllowed === false) {
                return false;
            }
        }

        // Check for "CMS admin" permission
        if (Permission::checkMember($member, "CMS_ACCESS_LeftAndMain")) {
            return true;
        }

        // Check for LeftAndMain sub-class permissions
        $codes = $this->getRequiredPermissions();
        if ($codes === false) { // allow explicit FALSE to disable subclass check
            return true;
        }
        foreach ((array)$codes as $code) {
            if (!Permission::checkMember($member, $code)) {
                return false;
            }
        }

        return true;
    }

    /**
     * Get list of required permissions
     *
     * @return array|string|bool Code, array of codes, or false if no permission required
     */
    public static function getRequiredPermissions()
    {
        $class = get_called_class();
        $code = Config::inst()->get($class, 'required_permission_codes');
        if ($code === false) {
            return false;
        }
        if ($code) {
            return $code;
        }
        return "CMS_ACCESS_" . $class;
    }

    /**
     * @uses LeftAndMainExtension->init()
     * @uses LeftAndMainExtension->accessedCMS()
     * @uses CMSMenu
     */
    protected function init()
    {
        parent::init();

        SSViewer::config()->update('rewrite_hash_links', false);
        ContentNegotiator::config()->update('enabled', false);

        // set language
        $member = Member::currentUser();
        if (!empty($member->Locale)) {
            i18n::set_locale($member->Locale);
        }
        if (!empty($member->DateFormat)) {
            i18n::config()->date_format = $member->DateFormat;
        }
        if (!empty($member->TimeFormat)) {
            i18n::config()->time_format = $member->TimeFormat;
        }

        // can't be done in cms/_config.php as locale is not set yet
        CMSMenu::add_link(
            'Help',
            _t('LeftAndMain.HELP', 'Help', 'Menu title'),
            LeftAndMain::config()->uninherited('help_link'),
            -2,
            array(
                'target' => '_blank'
            ),
            'font-icon-help-circled'
        );

        // Allow customisation of the access check by a extension
        // Also all the canView() check to execute Controller::redirect()
        if (!$this->canView() && !$this->getResponse()->isFinished()) {
            // When access /admin/, we should try a redirect to another part of the admin rather than be locked out
            $menu = $this->MainMenu();
            foreach ($menu as $candidate) {
                if ($candidate->Link &&
                    $candidate->Link != $this->Link()
                    && $candidate->MenuItem->controller
                    && singleton($candidate->MenuItem->controller)->canView()
                ) {
                    $this->redirect($candidate->Link);
                    return;
                }
            }

            if (Member::currentUser()) {
                Session::set("BackURL", null);
            }

            // if no alternate menu items have matched, return a permission error
            $messageSet = array(
                'default' => _t(
                    'LeftAndMain.PERMDEFAULT',
                    "You must be logged in to access the administration area; please enter your credentials below."
                ),
                'alreadyLoggedIn' => _t(
                    'LeftAndMain.PERMALREADY',
                    "I'm sorry, but you can't access that part of the CMS.  If you want to log in as someone else, do"
                    . " so below."
                ),
                'logInAgain' => _t(
                    'LeftAndMain.PERMAGAIN',
                    "You have been logged out of the CMS.  If you would like to log in again, enter a username and"
                    . " password below."
                ),
            );

            Security::permissionFailure($this, $messageSet);
            return;
        }

        // Don't continue if there's already been a redirection request.
        if ($this->redirectedTo()) {
            return;
        }

        // Audit logging hook
        if (empty($_REQUEST['executeForm']) && !$this->getRequest()->isAjax()) {
            $this->extend('accessedCMS');
        }

        // Set the members html editor config
        if (Member::currentUser()) {
            HTMLEditorConfig::set_active_identifier(Member::currentUser()->getHtmlEditorConfigForCMS());
        }

        // Set default values in the config if missing.  These things can't be defined in the config
        // file because insufficient information exists when that is being processed
        $htmlEditorConfig = HTMLEditorConfig::get_active();
        $htmlEditorConfig->setOption('language', TinyMCEConfig::get_tinymce_lang());

        Requirements::customScript("
            window.ss = window.ss || {};
            window.ss.config = " . $this->getCombinedClientConfig() . ";
        ");

        Requirements::javascript(FRAMEWORK_ADMIN_DIR . '/client/dist/js/vendor.js');
        Requirements::javascript(FRAMEWORK_ADMIN_DIR . '/client/dist/js/bundle.js');
        Requirements::css(ltrim(FRAMEWORK_ADMIN_DIR . '/client/dist/styles/bundle.css', '/'));

        Requirements::add_i18n_javascript(ltrim(FRAMEWORK_DIR . '/client/lang', '/'), false, true);
        Requirements::add_i18n_javascript(FRAMEWORK_ADMIN_DIR . '/client/lang', false, true);

        if (LeftAndMain::config()->uninherited('session_keepalive_ping')) {
            Requirements::javascript(FRAMEWORK_ADMIN_DIR . '/client/dist/js/LeftAndMain.Ping.js');
        }

        if (Director::isDev()) {
            // TODO Confuses jQuery.ondemand through document.write()
            Requirements::javascript(ADMIN_THIRDPARTY_DIR . '/jquery-entwine/src/jquery.entwine.inspector.js');
            Requirements::javascript(FRAMEWORK_ADMIN_DIR . '/client/dist/js/leaktools.js');
        }

        // Custom requirements
        $extraJs = $this->stat('extra_requirements_javascript');

        if ($extraJs) {
            foreach ($extraJs as $file => $config) {
                if (is_numeric($file)) {
                    $file = $config;
                }

                Requirements::javascript($file);
            }
        }

        $extraCss = $this->stat('extra_requirements_css');

        if ($extraCss) {
            foreach ($extraCss as $file => $config) {
                if (is_numeric($file)) {
                    $file = $config;
                    $config = array();
                }

                Requirements::css($file, isset($config['media']) ? $config['media'] : null);
            }
        }

        $extraThemedCss = $this->stat('extra_requirements_themedCss');

        if ($extraThemedCss) {
            foreach ($extraThemedCss as $file => $config) {
                if (is_numeric($file)) {
                    $file = $config;
                    $config = array();
                }

                Requirements::themedCSS($file, isset($config['media']) ? $config['media'] : null);
            }
        }

        $dummy = null;
        $this->extend('init', $dummy);

        // Assign default cms theme and replace user-specified themes
        SSViewer::set_themes(LeftAndMain::config()->uninherited('admin_themes'));

        //set the reading mode for the admin to stage
        Versioned::set_stage(Versioned::DRAFT);
    }

    public function handleRequest(HTTPRequest $request, DataModel $model = null)
    {
        try {
            $response = parent::handleRequest($request, $model);
        } catch (ValidationException $e) {
            // Nicer presentation of model-level validation errors
            $msgs = _t('LeftAndMain.ValidationError', 'Validation error') . ': '
                . $e->getMessage();
            $e = new HTTPResponse_Exception($msgs, 403);
            $errorResponse = $e->getResponse();
            $errorResponse->addHeader('Content-Type', 'text/plain');
            $errorResponse->addHeader('X-Status', rawurlencode($msgs));
            $e->setResponse($errorResponse);
            throw $e;
        }

        $title = $this->Title();
        if (!$response->getHeader('X-Controller')) {
            $response->addHeader('X-Controller', $this->class);
        }
        if (!$response->getHeader('X-Title')) {
            $response->addHeader('X-Title', urlencode($title));
        }

        // Prevent clickjacking, see https://developer.mozilla.org/en-US/docs/HTTP/X-Frame-Options
        $originalResponse = $this->getResponse();
        $originalResponse->addHeader('X-Frame-Options', LeftAndMain::config()->uninherited('frame_options'));
        $originalResponse->addHeader('Vary', 'X-Requested-With');

        return $response;
    }

    /**
     * Overloaded redirection logic to trigger a fake redirect on ajax requests.
     * While this violates HTTP principles, its the only way to work around the
     * fact that browsers handle HTTP redirects opaquely, no intervention via JS is possible.
     * In isolation, that's not a problem - but combined with history.pushState()
     * it means we would request the same redirection URL twice if we want to update the URL as well.
     * See LeftAndMain.js for the required jQuery ajaxComplete handlers.
     *
     * @param string $url
     * @param int $code
     * @return HTTPResponse|string
     */
    public function redirect($url, $code = 302)
    {
        if ($this->getRequest()->isAjax()) {
            $response = $this->getResponse();
            $response->addHeader('X-ControllerURL', $url);
            if ($this->getRequest()->getHeader('X-Pjax') && !$response->getHeader('X-Pjax')) {
                $response->addHeader('X-Pjax', $this->getRequest()->getHeader('X-Pjax'));
            }
            $newResponse = new LeftAndMain_HTTPResponse(
                $response->getBody(),
                $response->getStatusCode(),
                $response->getStatusDescription()
            );
            foreach ($response->getHeaders() as $k => $v) {
                $newResponse->addHeader($k, $v);
            }
            $newResponse->setIsFinished(true);
            $this->setResponse($newResponse);
            return ''; // Actual response will be re-requested by client
        } else {
            return parent::redirect($url, $code);
        }
    }

    /**
     * @param HTTPRequest $request
     * @return HTTPResponse
     */
    public function index($request)
    {
        return $this->getResponseNegotiator()->respond($request);
    }

    /**
     * If this is set to true, the "switchView" context in the
     * template is shown, with links to the staging and publish site.
     *
     * @return boolean
     */
    public function ShowSwitchView()
    {
        return false;
    }


    //------------------------------------------------------------------------------------------//
    // Main controllers

    /**
     * You should implement a Link() function in your subclass of LeftAndMain,
     * to point to the URL of that particular controller.
     *
     * @param string $action
     * @return string
     */
    public function Link($action = null)
    {
        // Handle missing url_segments
        $segment = $this->config()->get('url_segment')
            ?: $this->class;

        $link = Controller::join_links(
            AdminRootController::admin_url(),
            $segment,
            '/', // trailing slash needed if $action is null!
            "$action"
        );
        $this->extend('updateLink', $link);
        return $link;
    }

    /**
     * @deprecated 5.0
     */
    public static function menu_title_for_class($class)
    {
        Deprecation::notice('5.0', 'Use menu_title() instead');
        return static::menu_title($class, false);
    }

    /**
     * Get menu title for this section (translated)
     *
     * @param string $class Optional class name if called on LeftAndMain directly
     * @param bool $localise Determine if menu title should be localised via i18n.
     * @return string Menu title for the given class
     */
    public static function menu_title($class = null, $localise = true)
    {
        if ($class && is_subclass_of($class, __CLASS__)) {
            // Respect oveloading of menu_title() in subclasses
            return $class::menu_title(null, $localise);
        }
        if (!$class) {
            $class = get_called_class();
        }

        // Get default class title
        $title = static::config()->get('menu_title');
        if (!$title) {
            $title = preg_replace('/Admin$/', '', $class);
        }

        // Check localisation
        if (!$localise) {
            return $title;
        }
        return i18n::_t("{$class}.MENUTITLE", $title);
    }

    /**
     * Return styling for the menu icon, if a custom icon is set for this class
     *
     * Example: static $menu-icon = '/path/to/image/';
     * @param string $class
     * @return string
     */
    public static function menu_icon_for_class($class)
    {
        $icon = Config::inst()->get($class, 'menu_icon');
        if (!empty($icon)) {
            $class = strtolower(Convert::raw2htmlname(str_replace('\\', '-', $class)));
            return ".icon.icon-16.icon-{$class} { background-image: url('{$icon}'); } ";
        }
        return '';
    }

    /**
     * Return the web font icon class name for this interface icon. Uses the
     * built in SilveStripe webfont. {@see menu_icon_for_class()} for providing
     * a background image.
     *
     * @param string $class.
     * @return string
     */
    public static function menu_icon_class_for_class($class)
    {
        return Config::inst()->get($class, 'menu_icon_class');
    }

    /**
     * @param HTTPRequest $request
     * @return HTTPResponse
     * @throws HTTPResponse_Exception
     */
    public function show($request)
    {
        // TODO Necessary for TableListField URLs to work properly
        if ($request->param('ID')) {
            $this->setCurrentPageID($request->param('ID'));
        }
        return $this->getResponseNegotiator()->respond($request);
    }

    /**
     * Caution: Volatile API.
     *
     * @return PjaxResponseNegotiator
     */
    public function getResponseNegotiator()
    {
        if (!$this->responseNegotiator) {
            $controller = $this;
            $this->responseNegotiator = new PjaxResponseNegotiator(
                array(
                    'CurrentForm' => function () use (&$controller) {
                        return $controller->getEditForm()->forTemplate();
                    },
                    'Content' => function () use (&$controller) {
                        return $controller->renderWith($controller->getTemplatesWithSuffix('_Content'));
                    },
                    'Breadcrumbs' => function () use (&$controller) {
                        return $controller->renderWith([
                            'type' => 'Includes',
                            'SilverStripe\\Admin\\CMSBreadcrumbs'
                        ]);
                    },
                    'default' => function () use (&$controller) {
                        return $controller->renderWith($controller->getViewer('show'));
                    }
                ),
                $this->getResponse()
            );
        }
        return $this->responseNegotiator;
    }

    //------------------------------------------------------------------------------------------//
    // Main UI components

    /**
     * Returns the main menu of the CMS.  This is also used by init()
     * to work out which sections the user has access to.
     *
     * @param bool $cached
     * @return SS_List
     */
    public function MainMenu($cached = true)
    {
        if (!isset($this->_cache_MainMenu) || !$cached) {
            // Don't accidentally return a menu if you're not logged in - it's used to determine access.
            if (!Member::currentUser()) {
                return new ArrayList();
            }

            // Encode into DO set
            $menu = new ArrayList();
            $menuItems = CMSMenu::get_viewable_menu_items();

            // extra styling for custom menu-icons
            $menuIconStyling = '';

            if ($menuItems) {
                /** @var CMSMenuItem $menuItem */
                foreach ($menuItems as $code => $menuItem) {
                    // alternate permission checks (in addition to LeftAndMain->canView())
                    if (isset($menuItem->controller)
                        && $this->hasMethod('alternateMenuDisplayCheck')
                        && !$this->alternateMenuDisplayCheck($menuItem->controller)
                    ) {
                        continue;
                    }

                    $linkingmode = "link";

                    if ($menuItem->controller && get_class($this) == $menuItem->controller) {
                        $linkingmode = "current";
                    } elseif (strpos($this->Link(), $menuItem->url) !== false) {
                        if ($this->Link() == $menuItem->url) {
                            $linkingmode = "current";

                        // default menu is the one with a blank {@link url_segment}
                        } elseif (singleton($menuItem->controller)->stat('url_segment') == '') {
                            if ($this->Link() == AdminRootController::admin_url()) {
                                $linkingmode = "current";
                            }
                        } else {
                            $linkingmode = "current";
                        }
                    }

                    // already set in CMSMenu::populate_menu(), but from a static pre-controller
                    // context, so doesn't respect the current user locale in _t() calls - as a workaround,
                    // we simply call LeftAndMain::menu_title() again
                    // if we're dealing with a controller
                    if ($menuItem->controller) {
                        $title = LeftAndMain::menu_title($menuItem->controller);
                    } else {
                        $title = $menuItem->title;
                    }

                    // Provide styling for custom $menu-icon. Done here instead of in
                    // CMSMenu::populate_menu(), because the icon is part of
                    // the CMS right pane for the specified class as well...
                    if ($menuItem->controller) {
                        $menuIcon = LeftAndMain::menu_icon_for_class($menuItem->controller);

                        if (!empty($menuIcon)) {
                            $menuIconStyling .= $menuIcon;
                        }

                        $iconClass = LeftAndMain::menu_icon_class_for_class($menuItem->controller);
                    } else {
                        $iconClass = $menuItem->iconClass;
                    }

                    $menu->push(new ArrayData(array(
                        "MenuItem" => $menuItem,
                        "AttributesHTML" => $menuItem->getAttributesHTML(),
                        "Title" => Convert::raw2xml($title),
                        "Code" => $code,
                        "Icon" => strtolower($code),
                        "IconClass" => $iconClass,
                        "Link" => $menuItem->url,
                        "LinkingMode" => $linkingmode
                    )));
                }
            }
            if ($menuIconStyling) {
                Requirements::customCSS($menuIconStyling);
            }

            $this->_cache_MainMenu = $menu;
        }

        return $this->_cache_MainMenu;
    }

    public function Menu()
    {
        return $this->renderWith($this->getTemplatesWithSuffix('_Menu'));
    }

    /**
     * @todo Wrap in CMSMenu instance accessor
     * @return ArrayData A single menu entry (see {@link MainMenu})
     */
    public function MenuCurrentItem()
    {
        $items = $this->MainMenu();
        return $items->find('LinkingMode', 'current');
    }

    /**
     * Return a list of appropriate templates for this class, with the given suffix using
     * {@link SSViewer::get_templates_by_class()}
     *
     * @param string $suffix
     * @return array
     */
    public function getTemplatesWithSuffix($suffix)
    {
        $templates = SSViewer::get_templates_by_class(get_class($this), $suffix, __CLASS__);
        return SSViewer::chooseTemplate($templates);
    }

    public function Content()
    {
        return $this->renderWith($this->getTemplatesWithSuffix('_Content'));
    }

    /**
     * Render $PreviewPanel content
     *
     * @return DBHTMLText
     */
    public function PreviewPanel()
    {
        $template = $this->getTemplatesWithSuffix('_PreviewPanel');
        // Only render sections with preview panel
        if ($template) {
            return $this->renderWith($template);
        }
    }

    public function getRecord($id)
    {
        $className = $this->stat('tree_class');
        if ($className && $id instanceof $className) {
            return $id;
        } elseif ($className && $id == 'root') {
            return singleton($className);
        } elseif ($className && is_numeric($id)) {
            return DataObject::get_by_id($className, $id);
        } else {
            return false;
        }
    }

    /**
     * @param bool $unlinked
     * @return ArrayList
     */
    public function Breadcrumbs($unlinked = false)
    {
        $items = new ArrayList(array(
            new ArrayData(array(
                'Title' => $this->menu_title(),
                'Link' => ($unlinked) ? false : $this->Link()
            ))
        ));
        $record = $this->currentPage();
        if ($record && $record->exists()) {
            if ($record->hasExtension(Hierarchy::class)) {
                $ancestors = $record->getAncestors();
                $ancestors = new ArrayList(array_reverse($ancestors->toArray()));
                $ancestors->push($record);
                foreach ($ancestors as $ancestor) {
                    $items->push(new ArrayData(array(
                        'Title' => ($ancestor->MenuTitle) ? $ancestor->MenuTitle : $ancestor->Title,
                        'Link' => ($unlinked) ? false : Controller::join_links($this->Link('show'), $ancestor->ID)
                    )));
                }
            } else {
                $items->push(new ArrayData(array(
                    'Title' => ($record->MenuTitle) ? $record->MenuTitle : $record->Title,
                    'Link' => ($unlinked) ? false : Controller::join_links($this->Link('show'), $record->ID)
                )));
            }
        }

        return $items;
    }

    /**
     * @return String HTML
     */
    public function SiteTreeAsUL()
    {
        $html = $this->getSiteTreeFor($this->stat('tree_class'));
        $this->extend('updateSiteTreeAsUL', $html);
        return $html;
    }

    /**
     * Gets the current search filter for this request, if available
     *
     * @throws InvalidArgumentException
     * @return LeftAndMain_SearchFilter
     */
    protected function getSearchFilter()
    {
        // Check for given FilterClass
        $params = $this->getRequest()->getVar('q');
        if (empty($params['FilterClass'])) {
            return null;
        }

        // Validate classname
        $filterClass = $params['FilterClass'];
        $filterInfo = new ReflectionClass($filterClass);
        if (!$filterInfo->implementsInterface('SilverStripe\\Admin\\LeftAndMain_SearchFilter')) {
            throw new InvalidArgumentException(sprintf('Invalid filter class passed: %s', $filterClass));
        }

        return Injector::inst()->createWithArgs($filterClass, array($params));
    }

    /**
     * Get a site tree HTML listing which displays the nodes under the given criteria.
     *
     * @param string $className The class of the root object
     * @param string $rootID The ID of the root object.  If this is null then a complete tree will be
     *  shown
     * @param string $childrenMethod The method to call to get the children of the tree. For example,
     *  Children, AllChildrenIncludingDeleted, or AllHistoricalChildren
     * @param string $numChildrenMethod
     * @param callable $filterFunction
     * @param int $nodeCountThreshold
     * @return string Nested unordered list with links to each page
     */
    public function getSiteTreeFor(
        $className,
        $rootID = null,
        $childrenMethod = null,
        $numChildrenMethod = null,
        $filterFunction = null,
        $nodeCountThreshold = 30
    ) {

        // Filter criteria
        $filter = $this->getSearchFilter();

        // Default childrenMethod and numChildrenMethod
        if (!$childrenMethod) {
            $childrenMethod = ($filter && $filter->getChildrenMethod())
            ? $filter->getChildrenMethod()
            : 'AllChildrenIncludingDeleted';
        }

        if (!$numChildrenMethod) {
            $numChildrenMethod = 'numChildren';
            if ($filter && $filter->getNumChildrenMethod()) {
                $numChildrenMethod = $filter->getNumChildrenMethod();
            }
        }
        if (!$filterFunction && $filter) {
            $filterFunction = function ($node) use ($filter) {
                return $filter->isPageIncluded($node);
            };
        }

        // Get the tree root
        $record = ($rootID) ? $this->getRecord($rootID) : null;
        $obj = $record ? $record : singleton($className);

        // Get the current page
        // NOTE: This *must* be fetched before markPartialTree() is called, as this
        // causes the Hierarchy::$marked cache to be flushed (@see CMSMain::getRecord)
        // which means that deleted pages stored in the marked tree would be removed
        $currentPage = $this->currentPage();

        // Mark the nodes of the tree to return
        if ($filterFunction) {
            $obj->setMarkingFilterFunction($filterFunction);
        }

        $obj->markPartialTree($nodeCountThreshold, $this, $childrenMethod, $numChildrenMethod);

        // Ensure current page is exposed
        if ($currentPage) {
            $obj->markToExpose($currentPage);
        }

        // NOTE: SiteTree/CMSMain coupling :-(
        if (class_exists('SilverStripe\\CMS\\Model\\SiteTree')) {
            SiteTree::prepopulate_permission_cache(
                'CanEditType',
                $obj->markedNodeIDs(),
                'SilverStripe\\CMS\\Model\\SiteTree::can_edit_multiple'
            );
        }

        // getChildrenAsUL is a flexible and complex way of traversing the tree
        $controller = $this;
        $recordController = ($this->stat('tree_class') == 'SilverStripe\\CMS\\Model\\SiteTree')
            ?  CMSPageEditController::singleton()
            : $this;
        $titleFn = function (&$child, $numChildrenMethod) use (&$controller, &$recordController, $filter) {
            $link = Controller::join_links($recordController->Link("show"), $child->ID);
            $node = LeftAndMain_TreeNode::create($child, $link, $controller->isCurrentPage($child), $numChildrenMethod, $filter);
            return $node->forTemplate();
        };

        // Limit the amount of nodes shown for performance reasons.
        // Skip the check if we're filtering the tree, since its not clear how many children will
        // match the filter criteria until they're queried (and matched up with previously marked nodes).
        $nodeThresholdLeaf = Config::inst()->get(Hierarchy::class, 'node_threshold_leaf');
        if ($nodeThresholdLeaf && !$filterFunction) {
            $nodeCountCallback = function ($parent, $numChildren) use (&$controller, $className, $nodeThresholdLeaf) {
                if ($className !== 'SilverStripe\\CMS\\Model\\SiteTree'
                    || !$parent->ID
                    || $numChildren <= $nodeThresholdLeaf
                ) {
                    return null;
                }
                    return sprintf(
                        '<ul><li class="readonly"><span class="item">'
                            . '%s (<a href="%s" class="cms-panel-link" data-pjax-target="Content">%s</a>)'
                            . '</span></li></ul>',
                        _t('LeftAndMain.TooManyPages', 'Too many pages'),
                        Controller::join_links(
                            $controller->LinkWithSearch($controller->Link()),
                            '?view=listview&ParentID=' . $parent->ID
                        ),
                        _t(
                            'LeftAndMain.ShowAsList',
                            'show as list',
                            'Show large amount of pages in list instead of tree view'
                        )
                    );
            };
        } else {
            $nodeCountCallback = null;
        }

        // If the amount of pages exceeds the node thresholds set, use the callback
        $html = null;
        if ($obj->ParentID && $nodeCountCallback) {
            $html = $nodeCountCallback($obj, $obj->$numChildrenMethod());
        }

        // Otherwise return the actual tree (which might still filter leaf thresholds on children)
        if (!$html) {
            $html = $obj->getChildrenAsUL(
                "",
                $titleFn,
                CMSPagesController::singleton(),
                true,
                $childrenMethod,
                $numChildrenMethod,
                $nodeCountThreshold,
                $nodeCountCallback
            );
        }

        // Wrap the root if needs be.
        if (!$rootID) {
            $rootLink = $this->Link('show') . '/root';

            // This lets us override the tree title with an extension
            if ($this->hasMethod('getCMSTreeTitle') && $customTreeTitle = $this->getCMSTreeTitle()) {
                $treeTitle = $customTreeTitle;
            } elseif (class_exists('SilverStripe\\SiteConfig\\SiteConfig')) {
                $siteConfig = SiteConfig::current_site_config();
                $treeTitle =  Convert::raw2xml($siteConfig->Title);
            } else {
                $treeTitle = '...';
            }

            $html = "<ul><li id=\"record-0\" data-id=\"0\" class=\"Root nodelete\"><strong>$treeTitle</strong>"
                . $html . "</li></ul>";
        }

        return $html;
    }

    /**
     * Get a subtree underneath the request param 'ID'.
     * If ID = 0, then get the whole tree.
     *
     * @param HTTPRequest $request
     * @return string
     */
    public function getsubtree($request)
    {
        $html = $this->getSiteTreeFor(
            $this->stat('tree_class'),
            $request->getVar('ID'),
            null,
            null,
            null,
            $request->getVar('minNodeCount')
        );

        // Trim off the outer tag
        $html = preg_replace('/^[\s\t\r\n]*<ul[^>]*>/', '', $html);
        $html = preg_replace('/<\/ul[^>]*>[\s\t\r\n]*$/', '', $html);

        return $html;
    }

    /**
     * Allows requesting a view update on specific tree nodes.
     * Similar to {@link getsubtree()}, but doesn't enforce loading
     * all children with the node. Useful to refresh views after
     * state modifications, e.g. saving a form.
     *
     * @param HTTPRequest $request
     * @return string JSON
     */
    public function updatetreenodes($request)
    {
        $data = array();
        $ids = explode(',', $request->getVar('ids'));
        foreach ($ids as $id) {
            if ($id === "") {
                continue; // $id may be a blank string, which is invalid and should be skipped over
            }

            $record = $this->getRecord($id);
            if (!$record) {
                continue; // In case a page is no longer available
            }
            $recordController = ($this->stat('tree_class') == 'SilverStripe\\CMS\\Model\\SiteTree')
                ? CMSPageEditController::singleton()
                : $this;

            // Find the next & previous nodes, for proper positioning (Sort isn't good enough - it's not a raw offset)
            // TODO: These methods should really be in hierarchy - for a start it assumes Sort exists
            $next = $prev = null;

            $className = $this->stat('tree_class');
            $next = DataObject::get($className)
                ->filter('ParentID', $record->ParentID)
                ->filter('Sort:GreaterThan', $record->Sort)
                ->first();

            if (!$next) {
                $prev = DataObject::get($className)
                    ->filter('ParentID', $record->ParentID)
                    ->filter('Sort:LessThan', $record->Sort)
                    ->reverse()
                    ->first();
            }

            $link = Controller::join_links($recordController->Link("show"), $record->ID);
            $html = LeftAndMain_TreeNode::create($record, $link, $this->isCurrentPage($record))->forTemplate(). '</li>';

            $data[$id] = array(
                'html' => $html,
                'ParentID' => $record->ParentID,
                'NextID' => $next ? $next->ID : null,
                'PrevID' => $prev ? $prev->ID : null
            );
        }
        $this->getResponse()->addHeader('Content-Type', 'text/json');
        return Convert::raw2json($data);
    }

    /**
     * Save  handler
     *
     * @param array $data
     * @param Form $form
     * @return HTTPResponse
     */
    public function save($data, $form)
    {
        $request = $this->getRequest();
        $className = $this->stat('tree_class');

        // Existing or new record?
        $id = $data['ID'];
        if (is_numeric($id) && $id > 0) {
            $record = DataObject::get_by_id($className, $id);
            if ($record && !$record->canEdit()) {
                return Security::permissionFailure($this);
            }
            if (!$record || !$record->ID) {
                $this->httpError(404, "Bad record ID #" . (int)$id);
            }
        } else {
            if (!singleton($this->stat('tree_class'))->canCreate()) {
                return Security::permissionFailure($this);
            }
            $record = $this->getNewItem($id, false);
        }

        // save form data into record
        $form->saveInto($record, true);
        $record->write();
        $this->extend('onAfterSave', $record);
        $this->setCurrentPageID($record->ID);

        $message = _t('LeftAndMain.SAVEDUP', 'Saved.');
        if ($this->getSchemaRequested()) {
            $schemaId = Controller::join_links($this->Link('schema/DetailEditForm'), $id);
            // Ensure that newly created records have all their data loaded back into the form.
            $form->loadDataFrom($record);
            $form->setMessage($message, 'good');
            $response = $this->getSchemaResponse($schemaId, $form);
        } else {
            $response = $this->getResponseNegotiator()->respond($request);
        }

        $response->addHeader('X-Status', rawurlencode($message));
        return $response;
    }

    /**
     * Create new item.
     *
     * @param string|int $id
     * @param bool $setID
     * @return DataObject
     */
    public function getNewItem($id, $setID = true)
    {
        $class = $this->stat('tree_class');
        $object = Injector::inst()->create($class);
        if ($setID) {
            $object->ID = $id;
        }
        return $object;
    }

    public function delete($data, $form)
    {
        $className = $this->stat('tree_class');

        $id = $data['ID'];
        $record = DataObject::get_by_id($className, $id);
        if ($record && !$record->canDelete()) {
            return Security::permissionFailure();
        }
        if (!$record || !$record->ID) {
            $this->httpError(404, "Bad record ID #" . (int)$id);
        }

        $record->delete();

        $this->getResponse()->addHeader('X-Status', rawurlencode(_t('LeftAndMain.DELETED', 'Deleted.')));
        return $this->getResponseNegotiator()->respond(
            $this->getRequest(),
            array('currentform' => array($this, 'EmptyForm'))
        );
    }

    /**
     * Update the position and parent of a tree node.
     * Only saves the node if changes were made.
     *
     * Required data:
     * - 'ID': The moved node
     * - 'ParentID': New parent relation of the moved node (0 for root)
     * - 'SiblingIDs': Array of all sibling nodes to the moved node (incl. the node itself).
     *   In case of a 'ParentID' change, relates to the new siblings under the new parent.
     *
     * @param HTTPRequest $request
     * @return HTTPResponse JSON string with a
     * @throws HTTPResponse_Exception
     */
    public function savetreenode($request)
    {
        if (!SecurityToken::inst()->checkRequest($request)) {
            return $this->httpError(400);
        }
        if (!Permission::check('SITETREE_REORGANISE') && !Permission::check('ADMIN')) {
            $this->getResponse()->setStatusCode(
                403,
                _t(
                    'LeftAndMain.CANT_REORGANISE',
                    "You do not have permission to rearange the site tree. Your change was not saved."
                )
            );
            return;
        }

        $className = $this->stat('tree_class');
        $statusUpdates = array('modified'=>array());
        $id = $request->requestVar('ID');
        $parentID = $request->requestVar('ParentID');

        if ($className == 'SilverStripe\\CMS\\Model\\SiteTree' && $page = DataObject::get_by_id(SiteTree::class, $id)) {
            $root = $page->getParentType();
            if (($parentID == '0' || $root == 'root') && !SiteConfig::current_site_config()->canCreateTopLevel()) {
                $this->getResponse()->setStatusCode(
                    403,
                    _t(
                        'LeftAndMain.CANT_REORGANISE',
                        "You do not have permission to alter Top level pages. Your change was not saved."
                    )
                );
                return;
            }
        }

        $siblingIDs = $request->requestVar('SiblingIDs');
        $statusUpdates = array('modified'=>array());
        if (!is_numeric($id) || !is_numeric($parentID)) {
            throw new InvalidArgumentException();
        }

        $node = DataObject::get_by_id($className, $id);
        if ($node && !$node->canEdit()) {
            return Security::permissionFailure($this);
        }

        if (!$node) {
            $this->getResponse()->setStatusCode(
                500,
                _t(
                    'LeftAndMain.PLEASESAVE',
                    "Please Save Page: This page could not be updated because it hasn't been saved yet."
                )
            );
            return;
        }

        // Update hierarchy (only if ParentID changed)
        if ($node->ParentID != $parentID) {
            $node->ParentID = (int)$parentID;
            $node->write();

            $statusUpdates['modified'][$node->ID] = array(
                'TreeTitle'=>$node->TreeTitle
            );

            // Update all dependent pages
            if (class_exists('SilverStripe\\CMS\\Model\\VirtualPage')) {
                $virtualPages = VirtualPage::get()->filter("CopyContentFromID", $node->ID);
                foreach ($virtualPages as $virtualPage) {
                    $statusUpdates['modified'][$virtualPage->ID] = array(
                        'TreeTitle' => $virtualPage->TreeTitle()
                    );
                }
            }

            $this->getResponse()->addHeader(
                'X-Status',
                rawurlencode(_t('LeftAndMain.REORGANISATIONSUCCESSFUL', 'Reorganised the site tree successfully.'))
            );
        }

        // Update sorting
        if (is_array($siblingIDs)) {
            $counter = 0;
            foreach ($siblingIDs as $id) {
                if ($id == $node->ID) {
                    $node->Sort = ++$counter;
                    $node->write();
                    $statusUpdates['modified'][$node->ID] = array(
                        'TreeTitle' => $node->TreeTitle
                    );
                } elseif (is_numeric($id)) {
                    // Nodes that weren't "actually moved" shouldn't be registered as
                    // having been edited; do a direct SQL update instead
                    ++$counter;
                    $table = DataObject::getSchema()->baseDataTable($className);
                    DB::prepared_query(
                        "UPDATE \"$table\" SET \"Sort\" = ? WHERE \"ID\" = ?",
                        array($counter, $id)
                    );
                }
            }

            $this->getResponse()->addHeader(
                'X-Status',
                rawurlencode(_t('LeftAndMain.REORGANISATIONSUCCESSFUL', 'Reorganised the site tree successfully.'))
            );
        }

        return Convert::raw2json($statusUpdates);
    }

    public function CanOrganiseSitetree()
    {
        return !Permission::check('SITETREE_REORGANISE') && !Permission::check('ADMIN') ? false : true;
    }

    /**
     * Retrieves an edit form, either for display, or to process submitted data.
     * Also used in the template rendered through {@link Right()} in the $EditForm placeholder.
     *
     * This is a "pseudo-abstract" methoed, usually connected to a {@link getEditForm()}
     * method in an entwine subclass. This method can accept a record identifier,
     * selected either in custom logic, or through {@link currentPageID()}.
     * The form usually construct itself from {@link DataObject->getCMSFields()}
     * for the specific managed subclass defined in {@link LeftAndMain::$tree_class}.
     *
     * @param HTTPRequest $request Optionally contains an identifier for the
     *  record to load into the form.
     * @return Form Should return a form regardless wether a record has been found.
     *  Form might be readonly if the current user doesn't have the permission to edit
     *  the record.
     */
    /**
     * @return Form
     */
    public function EditForm($request = null)
    {
        return $this->getEditForm();
    }

    /**
     * Calls {@link SiteTree->getCMSFields()} by default to determine the form fields to display.
     *
     * @param int $id
     * @param FieldList $fields
     * @return Form
     */
    public function getEditForm($id = null, $fields = null)
    {
        if (!$id) {
            $id = $this->currentPageID();
        }

        if (is_object($id)) {
            $record = $id;
        } else {
            $record = $this->getRecord($id);
            if ($record && !$record->canView()) {
                return Security::permissionFailure($this);
            }
        }

        if ($record) {
            $fields = ($fields) ? $fields : $record->getCMSFields();
            if ($fields == null) {
                user_error(
                    "getCMSFields() returned null  - it should return a FieldList object.
                    Perhaps you forgot to put a return statement at the end of your method?",
                    E_USER_ERROR
                );
            }

            // Add hidden fields which are required for saving the record
            // and loading the UI state
            if (!$fields->dataFieldByName('ClassName')) {
                $fields->push(new HiddenField('ClassName'));
            }

            $tree_class = $this->stat('tree_class');
            if ($tree_class::has_extension(Hierarchy::class)
                && !$fields->dataFieldByName('ParentID')
            ) {
                $fields->push(new HiddenField('ParentID'));
            }

            // Added in-line to the form, but plucked into different view by frontend scripts.
            if ($record instanceof CMSPreviewable) {
                /** @skipUpgrade */
                $navField = new LiteralField('SilverStripeNavigator', $this->getSilverStripeNavigator());
                $navField->setAllowHTML(true);
                $fields->push($navField);
            }

            if ($record->hasMethod('getAllCMSActions')) {
                $actions = $record->getAllCMSActions();
            } else {
                $actions = $record->getCMSActions();
                // add default actions if none are defined
                if (!$actions || !$actions->count()) {
                    if ($record->hasMethod('canEdit') && $record->canEdit()) {
                        $actions->push(
                            FormAction::create('save', _t('CMSMain.SAVE', 'Save'))
                               ->addExtraClass('btn btn-primary')
                               ->addExtraClass('font-icon-add-circle')
                        );
                    }
                    if ($record->hasMethod('canDelete') && $record->canDelete()) {
                        $actions->push(
                            FormAction::create('delete', _t('ModelAdmin.DELETE', 'Delete'))
                                ->addExtraClass('btn btn-secondary')
                        );
                    }
                }
            }

            $negotiator = $this->getResponseNegotiator();
            $form = Form::create(
                $this,
                "EditForm",
                $fields,
                $actions
            )->setHTMLID('Form_EditForm');
            $form->addExtraClass('cms-edit-form');
            $form->loadDataFrom($record);
            $form->setTemplate($this->getTemplatesWithSuffix('_EditForm'));
            $form->setAttribute('data-pjax-fragment', 'CurrentForm');
            $form->setValidationResponseCallback(function (ValidationResult $errors) use ($negotiator, $form) {
                $request = $this->getRequest();
                if ($request->isAjax() && $negotiator) {
                    $result = $form->forTemplate();

                    return $negotiator->respond($request, array(
                        'CurrentForm' => function () use ($result) {
                            return $result;
                        }
                    ));
                }
            });

            // Announce the capability so the frontend can decide whether to allow preview or not.
            if ($record instanceof CMSPreviewable) {
                $form->addExtraClass('cms-previewable');
            }
            $form->addExtraClass('fill-height');

            // Set this if you want to split up tabs into a separate header row
            // if($form->Fields()->hasTabset()) {
            //     $form->Fields()->findOrMakeTab('Root')->setTemplate('SilverStripe\\Forms\\CMSTabSet');
            // }

            // Add a default or custom validator.
            // @todo Currently the default Validator.js implementation
            //  adds javascript to the document body, meaning it won't
            //  be included properly if the associated fields are loaded
            //  through ajax. This means only serverside validation
            //  will kick in for pages+validation loaded through ajax.
            //  This will be solved by using less obtrusive javascript validation
            //  in the future, see http://open.silverstripe.com/ticket/2915 and
            //  http://open.silverstripe.com/ticket/3386
            if ($record->hasMethod('getCMSValidator')) {
                $validator = $record->getCMSValidator();
                // The clientside (mainly LeftAndMain*.js) rely on ajax responses
                // which can be evaluated as javascript, hence we need
                // to override any global changes to the validation handler.
                if ($validator != null) {
                    $form->setValidator($validator);
                }
            } else {
                $form->unsetValidator();
            }

            if ($record->hasMethod('canEdit') && !$record->canEdit()) {
                $readonlyFields = $form->Fields()->makeReadonly();
                $form->setFields($readonlyFields);
            }
        } else {
            $form = $this->EmptyForm();
        }

        return $form;
    }

    /**
     * Returns a placeholder form, used by {@link getEditForm()} if no record is selected.
     * Our javascript logic always requires a form to be present in the CMS interface.
     *
     * @return Form
     */
    public function EmptyForm()
    {
        $form = Form::create(
            $this,
            "EditForm",
            new FieldList(
                // new HeaderField(
                //     'WelcomeHeader',
                //     $this->getApplicationName()
                // ),
                // new LiteralField(
                //     'WelcomeText',
                //     sprintf('<p id="WelcomeMessage">%s %s. %s</p>',
                //         _t('LeftAndMain_right_ss.WELCOMETO','Welcome to'),
                //         $this->getApplicationName(),
                //         _t('CHOOSEPAGE','Please choose an item from the left.')
                //     )
                // )
            ),
            new FieldList()
        )->setHTMLID('Form_EditForm');
        $form->unsetValidator();
        $form->addExtraClass('cms-edit-form');
        $form->addExtraClass('root-form');
        $form->setTemplate($this->getTemplatesWithSuffix('_EditForm'));
        $form->setAttribute('data-pjax-fragment', 'CurrentForm');

        return $form;
    }

    /**
     * Return the CMS's HTML-editor toolbar
     */
    public function EditorToolbar()
    {
        return HTMLEditorField_Toolbar::create($this, "EditorToolbar");
    }

    /**
     * Renders a panel containing tools which apply to all displayed
     * "content" (mostly through {@link EditForm()}), for example a tree navigation or a filter panel.
     * Auto-detects applicable templates by naming convention: "<controller classname>_Tools.ss",
     * and takes the most specific template (see {@link getTemplatesWithSuffix()}).
     * To explicitly disable the panel in the subclass, simply create a more specific, empty template.
     *
     * @return String HTML
     */
    public function Tools()
    {
        $templates = $this->getTemplatesWithSuffix('_Tools');
        if ($templates) {
            $viewer = new SSViewer($templates);
            return $viewer->process($this);
        } else {
            return false;
        }
    }

    /**
     * Renders a panel containing tools which apply to the currently displayed edit form.
     * The main difference to {@link Tools()} is that the panel is displayed within
     * the element structure of the form panel (rendered through {@link EditForm}).
     * This means the panel will be loaded alongside new forms, and refreshed upon save,
     * which can mean a performance hit, depending on how complex your panel logic gets.
     * Any form fields contained in the returned markup will also be submitted with the main form,
     * which might be desired depending on the implementation details.
     *
     * @return String HTML
     */
    public function EditFormTools()
    {
        $templates = $this->getTemplatesWithSuffix('_EditFormTools');
        if ($templates) {
            $viewer = new SSViewer($templates);
            return $viewer->process($this);
        } else {
            return false;
        }
    }

    /**
     * Batch Actions Handler
     */
    public function batchactions()
    {
        return new CMSBatchActionHandler($this, 'batchactions', $this->stat('tree_class'));
    }

    /**
     * @return Form
     */
    public function BatchActionsForm()
    {
        $actions = $this->batchactions()->batchActionList();
        $actionsMap = array('-1' => _t('LeftAndMain.DropdownBatchActionsDefault', 'Choose an action...')); // Placeholder action
        foreach ($actions as $action) {
            $actionsMap[$action->Link] = $action->Title;
        }

        $form = new Form(
            $this,
            'BatchActionsForm',
            new FieldList(
                new HiddenField('csvIDs'),
                DropdownField::create(
                    'Action',
                    false,
                    $actionsMap
                )
                    ->setAttribute('autocomplete', 'off')
                    ->setAttribute('data-placeholder', _t('LeftAndMain.DropdownBatchActionsDefault', 'Choose an action...'))
            ),
            new FieldList(
                FormAction::create('submit', _t('Form.SubmitBtnLabel', "Go"))
                    ->addExtraClass('btn-secondary-outline')
            )
        );
        $form->addExtraClass('cms-batch-actions form--no-dividers');
        $form->unsetValidator();

        $this->extend('updateBatchActionsForm', $form);
        return $form;
    }

    public function printable()
    {
        $form = $this->getEditForm($this->currentPageID());
        if (!$form) {
            return false;
        }

        $form->transform(new PrintableTransformation());
        $form->setActions(null);

        Requirements::clear();
        Requirements::css(FRAMEWORK_ADMIN_DIR . '/dist/css/LeftAndMain_printable.css');
        return array(
            "PrintForm" => $form
        );
    }

    /**
     * Used for preview controls, mainly links which switch between different states of the page.
     *
     * @return DBHTMLText
     */
    public function getSilverStripeNavigator()
    {
        $page = $this->currentPage();
        if ($page instanceof CMSPreviewable) {
            $navigator = new SilverStripeNavigator($page);
            return $navigator->renderWith($this->getTemplatesWithSuffix('_SilverStripeNavigator'));
        }
        return null;
    }

    /**
     * Identifier for the currently shown record,
     * in most cases a database ID. Inspects the following
     * sources (in this order):
     * - GET/POST parameter named 'ID'
     * - URL parameter named 'ID'
     * - Session value namespaced by classname, e.g. "CMSMain.currentPage"
     *
     * @return int
     */
    public function currentPageID()
    {
        if ($this->getRequest()->requestVar('ID') && is_numeric($this->getRequest()->requestVar('ID'))) {
            return $this->getRequest()->requestVar('ID');
        } elseif ($this->getRequest()->requestVar('CMSMainCurrentPageID') && is_numeric($this->getRequest()->requestVar('CMSMainCurrentPageID'))) {
            // see GridFieldDetailForm::ItemEditForm
            return $this->getRequest()->requestVar('CMSMainCurrentPageID');
        } elseif (isset($this->urlParams['ID']) && is_numeric($this->urlParams['ID'])) {
            return $this->urlParams['ID'];
        } elseif (Session::get($this->sessionNamespace() . ".currentPage")) {
            return Session::get($this->sessionNamespace() . ".currentPage");
        } else {
            return null;
        }
    }

    /**
     * Forces the current page to be set in session,
     * which can be retrieved later through {@link currentPageID()}.
     * Keep in mind that setting an ID through GET/POST or
     * as a URL parameter will overrule this value.
     *
     * @param int $id
     */
    public function setCurrentPageID($id)
    {
        $id = (int)$id;
        Session::set($this->sessionNamespace() . ".currentPage", $id);
    }

    /**
     * Uses {@link getRecord()} and {@link currentPageID()}
     * to get the currently selected record.
     *
     * @return DataObject
     */
    public function currentPage()
    {
        return $this->getRecord($this->currentPageID());
    }

    /**
     * Compares a given record to the currently selected one (if any).
     * Used for marking the current tree node.
     *
     * @param DataObject $record
     * @return bool
     */
    public function isCurrentPage(DataObject $record)
    {
        return ($record->ID == $this->currentPageID());
    }

    /**
     * @return String
     */
    protected function sessionNamespace()
    {
        $override = $this->stat('session_namespace');
        return $override ? $override : $this->class;
    }

    /**
     * URL to a previewable record which is shown through this controller.
     * The controller might not have any previewable content, in which case
     * this method returns FALSE.
     *
     * @return String|boolean
     */
    public function LinkPreview()
    {
        return false;
    }

    /**
     * Return the version number of this application.
     * Uses the number in <mymodule>/silverstripe_version
     * (automatically replaced by build scripts).
     * If silverstripe_version is empty,
     * then attempts to get it from composer.lock
     *
     * @return string
     */
    public function CMSVersion()
    {
        $versions = array();
        $modules = array(
            'silverstripe/framework' => array(
                'title' => 'Framework',
                'versionFile' => FRAMEWORK_PATH . '/silverstripe_version',
            )
        );
        if (defined('CMS_PATH')) {
            $modules['silverstripe/cms'] = array(
                'title' => 'CMS',
                'versionFile' => CMS_PATH . '/silverstripe_version',
            );
        }

        // Tries to obtain version number from composer.lock if it exists
        $composerLockPath = BASE_PATH . '/composer.lock';
        if (file_exists($composerLockPath)) {
            $cache = Injector::inst()->get(CacheInterface::class . '.LeftAndMain_CMSVersion');
            $cacheKey = (string)filemtime($composerLockPath);
            $versions = $cache->get($cacheKey);
            if ($versions) {
                $versions = json_decode($versions, true);
            } else {
                $versions = array();
            }
            if (!$versions && $jsonData = file_get_contents($composerLockPath)) {
                $lockData = json_decode($jsonData);
                if ($lockData && isset($lockData->packages)) {
                    foreach ($lockData->packages as $package) {
                        if (array_key_exists($package->name, $modules)
                            && isset($package->version)
                        ) {
                            $versions[$package->name] = $package->version;
                        }
                    }
                    $cache->set($cacheKey, json_encode($versions));
                }
            }
        }

        // Fall back to static version file
        foreach ($modules as $moduleName => $moduleSpec) {
            if (!isset($versions[$moduleName])) {
                if ($staticVersion = file_get_contents($moduleSpec['versionFile'])) {
                    $versions[$moduleName] = $staticVersion;
                } else {
                    $versions[$moduleName] = _t('LeftAndMain.VersionUnknown', 'Unknown');
                }
            }
        }

        $out = array();
        foreach ($modules as $moduleName => $moduleSpec) {
            $out[] = $modules[$moduleName]['title'] . ': ' . $versions[$moduleName];
        }
        return implode(', ', $out);
    }

    /**
     * @return array
     */
    public function SwitchView()
    {
        if ($page = $this->currentPage()) {
            $nav = SilverStripeNavigator::get_for_record($page);
            return $nav['items'];
        }
    }

    /**
     * @return SiteConfig
     */
    public function SiteConfig()
    {
        return (class_exists('SilverStripe\\SiteConfig\\SiteConfig')) ? SiteConfig::current_site_config() : null;
    }

    /**
     * The href for the anchor on the Silverstripe logo.
     * Set by calling LeftAndMain::set_application_link()
     *
     * @config
     * @var String
     */
    private static $application_link = '//www.silverstripe.org/';

    /**
     * @return String
     */
    public function ApplicationLink()
    {
        return $this->stat('application_link');
    }

    /**
     * The application name. Customisable by calling
     * LeftAndMain::setApplicationName() - the first parameter.
     *
     * @config
     * @var String
     */
    private static $application_name = 'SilverStripe';

    /**
     * Get the application name.
     *
     * @return string
     */
    public function getApplicationName()
    {
        return $this->stat('application_name');
    }

    /**
     * @return string
     */
    public function Title()
    {
        $app = $this->getApplicationName();

        return ($section = $this->SectionTitle()) ? sprintf('%s - %s', $app, $section) : $app;
    }

    /**
     * Return the title of the current section. Either this is pulled from
     * the current panel's menu_title or from the first active menu
     *
     * @return string
     */
    public function SectionTitle()
    {
        $title = $this->menu_title();
        if ($title) {
            return $title;
        }

        foreach ($this->MainMenu() as $menuItem) {
            if ($menuItem->LinkingMode != 'link') {
                return $menuItem->Title;
            }
        }
    }

    /**
     * Same as {@link ViewableData->CSSClasses()}, but with a changed name
     * to avoid problems when using {@link ViewableData->customise()}
     * (which always returns "ArrayData" from the $original object).
     *
     * @return String
     */
    public function BaseCSSClasses()
    {
        return $this->CSSClasses('SilverStripe\\Control\\Controller');
    }

    /**
     * @return String
     */
    public function Locale()
    {
        return DBField::create_field('Locale', i18n::get_locale());
    }

    public function providePermissions()
    {
        $perms = array(
            "CMS_ACCESS_LeftAndMain" => array(
                'name' => _t('CMSMain.ACCESSALLINTERFACES', 'Access to all CMS sections'),
                'category' => _t('Permission.CMS_ACCESS_CATEGORY', 'CMS Access'),
                'help' => _t('CMSMain.ACCESSALLINTERFACESHELP', 'Overrules more specific access settings.'),
                'sort' => -100
            )
        );

        // Add any custom ModelAdmin subclasses. Can't put this on ModelAdmin itself
        // since its marked abstract, and needs to be singleton instanciated.
        foreach (ClassInfo::subclassesFor('SilverStripe\\Admin\\ModelAdmin') as $i => $class) {
            if ($class == 'SilverStripe\\Admin\\ModelAdmin') {
                continue;
            }
            if (ClassInfo::classImplements($class, 'SilverStripe\\Dev\\TestOnly')) {
                continue;
            }

            // Check if modeladmin has explicit required_permission_codes option.
            // If a modeladmin is namespaced you can apply this config to override
            // the default permission generation based on fully qualified class name.
            $code = $this->getRequiredPermissions();
            if (!$code) {
                continue;
            }
            // Get first permission if multiple specified
            if (is_array($code)) {
                $code = reset($code);
            }
            $title = LeftAndMain::menu_title($class);
            $perms[$code] = array(
                'name' => _t(
                    'CMSMain.ACCESS',
                    "Access to '{title}' section",
                    "Item in permission selection identifying the admin section. Example: Access to 'Files & Images'",
                    array('title' => $title)
                ),
                'category' => _t('Permission.CMS_ACCESS_CATEGORY', 'CMS Access')
            );
        }

        return $perms;
    }
}