ext_localconf.php

<?php

if (!defined('TYPO3_MODE')) {
    die('Access denied.');
}

/*
 * Add page typoscript for new content element wizard
 */
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPageTSConfig('<INCLUDE_TYPOSCRIPT: source="FILE:EXT:'.$_EXTKEY.'/Configuration/PageTS/tsconfig.txt">');

/*
 * Register hook to inject themes
 */
    $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['Tx_Themes_Domain_Repository_ThemeRepository']['init'][]
        = 'KayStrobach\\Themes\\Hooks\\ThemesDomainRepositoryThemeRepositoryInitHook->init';

/*
 * register used hooks to inject the TS
 */
    $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_tstemplate.php']['includeStaticTypoScriptSourcesAtEnd'][]
        = 'KayStrobach\\Themes\\Hooks\\T3libTstemplateIncludeStaticTypoScriptSourcesAtEndHook->main';

/*
 * register hook to manipulate the template module
 */
    $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['typo3/template.php']['moduleBodyPostProcess'][]
        = 'KayStrobach\\Themes\\Hooks\\TemplateModuleBodyPostProcessHook->main';

    /**
     * register signal to inject pagets without xclassing
     * Requires signal slot call from http://forge.typo3.org/issues/59703.
     *
     * @var \TYPO3\CMS\Extbase\SignalSlot\Dispatcher
     */
    $signalSlotDispatcher = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('TYPO3\\CMS\\Extbase\\SignalSlot\\Dispatcher');
    $signalSlotDispatcher->connect(
        'TYPO3\\CMS\\Backend\\Utility\\BackendUtility',
        'getPagesTSconfigPreInclude',
        'KayStrobach\\Themes\\Slots\\BackendUtilitySlot',
        'getPagesTsConfigPreInclude'
    );
    unset($signalSlotDispatcher);

/*
 * register hook to inject BeLayoutTsprovider
 */
    if (TYPO3_MODE === 'BE') {
        $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['BackendLayoutDataProvider']['pagets']
            = 'KayStrobach\\Themes\\Provider\\PageTsBackendLayoutDataProvider';
    }

/*
 * register command controller
 */
    $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['extbase']['commandControllers'][] = 'KayStrobach\Themes\Command\ThemesCommandController';

/*
 * register frontend plugin to allow usage of extbase controller
 */
    \TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin(
        'KayStrobach.'.$_EXTKEY,
        'Theme', [
            'Theme' => 'index',
        ],
        []
    );

/*
 * register cache for extension
 */
    if (!is_array($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['themes_cache'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['themes_cache'] = [];
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['themes_cache']['frontend'] = 'TYPO3\\CMS\\Core\\Cache\\Frontend\\VariableFrontend';
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['themes_cache']['backend'] = 'TYPO3\\CMS\\Core\\Cache\\Backend\\Typo3DatabaseBackend';
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['themes_cache']['options']['compression'] = 1;
    }

/*
 * Get YAML parser
 */
if (!class_exists('\Symfony\Component\Yaml\Parser')) {
    include_once \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::extPath('themes').'/Resources/Private/PHP/vendor/autoload.php';
}