wp.php

<?php

class ThemeUpdateHandler {
	/**
	 * Checks if the current version of the base theme is old, triggers
	 * and update message if it is.
	 *
	 * If a new version is available, we save the new version number to the database,
	 * so we can pull it back later and run version specific upgrades
	 *
	 * @param $transient:object
	 */
	public function check($transient) {
		if(!empty($transient->checked[get_config('paths')['parent-theme']])) {
			$ch = curl_init();

			curl_setopt($ch, CURLOPT_URL, get_config('update')['json']);

			curl_setopt($ch, CURLOPT_TIMEOUT, 3);
			curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

			$result = curl_exec($ch);

			if(curl_exec($ch) === false) {
				debug_log('CURL failed on theme update json file, error code:' . curl_errno($ch));
			} elseif(!empty($result)) {
				$data = json_decode($result, true);

				if(version_compare($transient->checked[get_config('paths')['parent-theme']], $data['new_version'], '<')) {
					$versions = json_encode(array('new' => $data['new_version'], 'old' => $transient->checked[get_config('paths')['parent-theme']]));

					if(!get_option('pm_upgrade_versions')) {
						add_option('pm_upgrade_versions', $versions); 
					} else {
						update_option('pm_upgrade_versions', $versions);
					}

					$transient->response[get_config('paths')['parent-theme']] = (array) $data;
				}
			}

			curl_close($ch);
		}

		return $transient;
	}
}
	
$handler = new ThemeUpdateHandler;

add_filter('pre_set_site_transient_update_themes', array($handler, 'check'));