Method checkExtensionInFilesystem

/**
 * Method to check if the extension is present in the filesystem
 *
 * @return  boolean
 *
 * @since   3.4
 * @throws  \RuntimeException
 */
protected function checkExtensionInFilesystem()
{
    /*
     * If the component site or admin directory already exists, then we will assume that the component is already
     * installed or another component is using that directory.
     */
    if (file_exists($this->parent->getPath('extension_site')) || file_exists($this->parent->getPath('extension_administrator')) || file_exists($this->parent->getPath('extension_api'))) {
        // Look for an update function or update tag
        $updateElement = $this->getManifest()->update;
        // Upgrade manually set or update function available or update tag detected
        if ($updateElement || $this->parent->isUpgrade() || $this->parent->manifestClass && method_exists($this->parent->manifestClass, 'update')) {
            // If there is a matching extension mark this as an update
            $this->setRoute('update');
        } elseif (!$this->parent->isOverwrite()) {
            // We didn't have overwrite set, find an update function or find an update tag so lets call it safe
            if (file_exists($this->parent->getPath('extension_site'))) {
                // If the site exists say so.
                throw new \RuntimeException(Text::sprintf('JLIB_INSTALLER_ERROR_COMP_INSTALL_DIR_SITE', $this->parent->getPath('extension_site')));
            }
            if (file_exists($this->parent->getPath('extension_administrator'))) {
                // If the admin exists say so
                throw new \RuntimeException(Text::sprintf('JLIB_INSTALLER_ERROR_COMP_INSTALL_DIR_ADMIN', $this->parent->getPath('extension_administrator')));
            }
            // If the API exists say so
            throw new \RuntimeException(Text::sprintf('JLIB_INSTALLER_ERROR_COMP_INSTALL_DIR_API', $this->parent->getPath('extension_api')));
        }
    }
    return false;
}