<?php
/**
 * Plugin Update Checker Library 2.0.0
 * http://w-shadow.com/
 *
 * Copyright 2015 Janis Elsts
 * Released under the  MIT license. See license.txt for details.
 */

if ( !class_exists('PluginUpdateChecker_2_0') ):

/**
 * A custom plugin update checker.
 *
 * @author Janis Elsts
 * @copyright 2015
 * @version 2.0
 * @access public
 */
class PluginUpdateChecker_2_0 {
    public $metadataUrl = ''; //The URL of the plugin's metadata file.
    public $pluginAbsolutePath = ''; //Full path of the main plugin file.
    public $pluginFile = '';  //Plugin filename relative to the plugins directory. Many WP APIs use this to identify plugins.
    public $slug = '';        //Plugin slug.
    public $checkPeriod = 12; //How often to check for updates (in hours).
    public $optionName = '';  //Where to store the update info.
    public $muPluginFile = ''; //For MU plugins, the plugin filename relative to the mu-plugins directory.

    public $debugMode = false; //Set to TRUE to enable error reporting. Errors are raised using trigger_error()
                               //and should be logged to the standard PHP error log.

    public $throttleRedundantChecks = false; //Check less often if we already know that an update is available.
    public $throttledCheckPeriod = 72;

    public $purchaseCode = false;

    private $cronHook = null;
    private $debugBarPlugin = null;
    private $cachedInstalledVersion = null;

    /**
     * Class constructor.
     *
     * @param string $metadataUrl The URL of the plugin's metadata file.
     * @param string $pluginFile Fully qualified path to the main plugin file.
     * @param string $slug The plugin's 'slug'. If not specified, the filename part of $pluginFile sans '.php' will be used as the slug.
     * @param integer $checkPeriod How often to check for updates (in hours). Defaults to checking every 12 hours. Set to 0 to disable automatic update checks.
     * @param string $optionName Where to store book-keeping info about update checks. Defaults to 'external_updates-$slug'.
     * @param string $muPluginFile Optional. The plugin filename relative to the mu-plugins directory.
     */
    public function __construct($metadataUrl, $pluginFile, $slug = '', $checkPeriod = 12, $optionName = '', $muPluginFile = ''){
        $this->metadataUrl = $metadataUrl;
        $this->pluginAbsolutePath = $pluginFile;
        $this->pluginFile = plugin_basename($this->pluginAbsolutePath);
        $this->muPluginFile = $muPluginFile;
        $this->checkPeriod = $checkPeriod;
        $this->slug = $slug;
        $this->optionName = $optionName;
        $this->debugMode = defined('WP_DEBUG') && WP_DEBUG;

        //If no slug is specified, use the name of the main plugin file as the slug.
        //For example, 'my-cool-plugin/cool-plugin.php' becomes 'cool-plugin'.
        if ( empty($this->slug) ){
            $this->slug = basename($this->pluginFile, '.php');
        }

        if ( empty($this->optionName) ){
            $this->optionName = 'external_updates-' . $this->slug;
        }

        //Backwards compatibility: If the plugin is a mu-plugin but no $muPluginFile is specified, assume
        //it's the same as $pluginFile given that it's not in a subdirectory (WP only looks in the base dir).
        if ( empty($this->muPluginFile) && (strpbrk($this->pluginFile, '/\\') === false) && $this->isMuPlugin() ) {
            $this->muPluginFile = $this->pluginFile;
        }

        $this->installHooks();
    }

    /**
     * Install the hooks required to run periodic update checks and inject update info
     * into WP data structures.
     *
     * @return void
     */
    protected function installHooks(){
        //Override requests for plugin information
        add_filter('plugins_api', array($this, 'injectInfo'), 20, 3);

        //Insert our update info into the update array maintained by WP
        add_filter('site_transient_update_plugins', array($this,'injectUpdate')); //WP 3.0+
        add_filter('transient_update_plugins', array($this,'injectUpdate')); //WP 2.8+

        add_filter('plugin_row_meta', array($this, 'addCheckForUpdatesLink'), 10, 2);
        add_action('admin_init', array($this, 'handleManualCheck'));
        add_action('all_admin_notices', array($this, 'displayManualCheckResult'));

        //Clear the version number cache when something - anything - is upgraded or WP clears the update cache.
        add_filter('upgrader_post_install', array($this, 'clearCachedVersion'));
        add_action('delete_site_transient_update_plugins', array($this, 'clearCachedVersion'));

        //Set up the periodic update checks
        $this->cronHook = 'check_plugin_updates-' . $this->slug;
        if ( $this->checkPeriod > 0 ){

            //Trigger the check via Cron.
            //Try to use one of the default schedules if possible as it's less likely to conflict
            //with other plugins and their custom schedules.
            $defaultSchedules = array(
                1  => 'hourly',
                12 => 'twicedaily',
                24 => 'daily',
            );
            if ( array_key_exists($this->checkPeriod, $defaultSchedules) ) {
                $scheduleName = $defaultSchedules[$this->checkPeriod];
            } else {
                //Use a custom cron schedule.
                $scheduleName = 'every' . $this->checkPeriod . 'hours';
                add_filter('cron_schedules', array($this, '_addCustomSchedule'));
            }

            if ( !wp_next_scheduled($this->cronHook) && !defined('WP_INSTALLING') ) {
                wp_schedule_event(time(), $scheduleName, $this->cronHook);
            }
            add_action($this->cronHook, array($this, 'maybeCheckForUpdates'));

            register_deactivation_hook($this->pluginFile, array($this, '_removeUpdaterCron'));

            //In case Cron is disabled or unreliable, we also manually trigger
            //the periodic checks while the user is browsing the Dashboard.
            add_action( 'admin_init', array($this, 'maybeCheckForUpdates') );

            //Like WordPress itself, we check more often on certain pages.
            /** @see wp_update_plugins */
            add_action('load-update-core.php', array($this, 'maybeCheckForUpdates'));
            add_action('load-plugins.php', array($this, 'maybeCheckForUpdates'));
            add_action('load-update.php', array($this, 'maybeCheckForUpdates'));
            //This hook fires after a bulk update is complete.
            add_action('upgrader_process_complete', array($this, 'maybeCheckForUpdates'), 11, 0);

        } else {
            //Periodic checks are disabled.
            wp_clear_scheduled_hook($this->cronHook);
        }

        if ( did_action('plugins_loaded') ) {
            $this->initDebugBarPanel();
        } else {
            add_action('plugins_loaded', array($this, 'initDebugBarPanel'));
        }

        //Rename the update directory to be the same as the existing directory.
        add_filter('upgrader_source_selection', array($this, 'fixDirectoryName'), 10, 3);
    }

    /**
     * Add our custom schedule to the array of Cron schedules used by WP.
     *
     * @param array $schedules
     * @return array
     */
    public function _addCustomSchedule($schedules){
        if ( $this->checkPeriod && ($this->checkPeriod > 0) ){
            $scheduleName = 'every' . $this->checkPeriod . 'hours';
            $schedules[$scheduleName] = array(
                'interval' => $this->checkPeriod * 3600,
                'display' => sprintf('Every %d hours', $this->checkPeriod),
            );
        }
        return $schedules;
    }

    /**
     * Remove the scheduled cron event that the library uses to check for updates.
     *
     * @return void
     */
    public function _removeUpdaterCron(){
        wp_clear_scheduled_hook($this->cronHook);
    }

    /**
     * Get the name of the update checker's WP-cron hook. Mostly useful for debugging.
     *
     * @return string
     */
    public function getCronHookName() {
        return $this->cronHook;
    }

    /**
     * Retrieve plugin info from the configured API endpoint.
     *
     * @uses wp_remote_get()
     *
     * @param array $queryArgs Additional query arguments to append to the request. Optional.
     * @return PluginInfo
     */
    public function requestInfo($queryArgs = array()){
        //Query args to append to the URL. Plugins can add their own by using a filter callback (see addQueryArgFilter()).
        $installedVersion = $this->getInstalledVersion();
        $queryArgs['installed_version'] = ($installedVersion !== null) ? $installedVersion : '';
        if($this->purchaseCode) {
            $queryArgs['code'] = $this->purchaseCode;
        }
        $queryArgs = apply_filters('puc_request_info_query_args-'.$this->slug, $queryArgs);

        //Various options for the wp_remote_get() call. Plugins can filter these, too.
        $options = array(
            'timeout' => 10, //seconds
            'headers' => array(
                'Accept' => 'application/json'
            ),
        );
        $options = apply_filters('puc_request_info_options-'.$this->slug, $options);

        //The plugin info should be at 'http://your-api.com/url/here/$slug/info.json'
        $url = $this->metadataUrl;
        if ( !empty($queryArgs) ){
            $url = add_query_arg($queryArgs, $url);
        }

        $result = wp_remote_get(
            $url,
            $options
        );

        //Try to parse the response
        $pluginInfo = null;
        if ( !is_wp_error($result) && isset($result['response']['code']) && ($result['response']['code'] == 200) && !empty($result['body']) ){
            $pluginInfo = PluginInfo_2_0::fromJson($result['body'], $this->debugMode);
            $pluginInfo->filename = $this->pluginFile;
            $pluginInfo->slug = $this->slug;
        } else if ( $this->debugMode ) {
            $message = sprintf("The URL %s does not point to a valid plugin metadata file. ", $url);
            if ( is_wp_error($result) ) {
                $message .= "WP HTTP error: " . $result->get_error_message();
            } else if ( isset($result['response']['code']) ) {
                $message .= "HTTP response code is " . $result['response']['code'] . " (expected: 200)";
            } else {
                $message .= "wp_remote_get() returned an unexpected result.";
            }
            trigger_error($message, E_USER_WARNING);
        }

        $pluginInfo = apply_filters('puc_request_info_result-'.$this->slug, $pluginInfo, $result);
        return $pluginInfo;
    }

    /**
     * Retrieve the latest update (if any) from the configured API endpoint.
     *
     * @uses PluginUpdateChecker::requestInfo()
     *
     * @return PluginUpdate An instance of PluginUpdate, or NULL when no updates are available.
     */
    public function requestUpdate(){
        //For the sake of simplicity, this function just calls requestInfo()
        //and transforms the result accordingly.
        $pluginInfo = $this->requestInfo(array('checking_for_updates' => '1'));
        if ( $pluginInfo == null ){
            return null;
        }
        return PluginUpdate_2_0::fromPluginInfo($pluginInfo);
    }

    /**
     * Get the currently installed version of the plugin.
     *
     * @return string Version number.
     */
    public function getInstalledVersion(){
        if ( isset($this->cachedInstalledVersion) ) {
            return $this->cachedInstalledVersion;
        }

        $pluginHeader = $this->getPluginHeader();
        if ( isset($pluginHeader['Version']) ) {
            $this->cachedInstalledVersion = $pluginHeader['Version'];
            return $pluginHeader['Version'];
        } else {
            //This can happen if the filename points to something that is not a plugin.
            if ( $this->debugMode ) {
                trigger_error(
                    sprintf(
                        "Can't to read the Version header for '%s'. The filename is incorrect or is not a plugin.",
                        $this->pluginFile
                    ),
                    E_USER_WARNING
                );
            }
            return null;
        }
    }

    /**
     * Get plugin's metadata from its file header.
     *
     * @return array
     */
    protected function getPluginHeader() {
        if ( !is_file($this->pluginAbsolutePath) ) {
            //This can happen if the plugin filename is wrong.
            if ( $this->debugMode ) {
                trigger_error(
                    sprintf(
                        "Can't to read the plugin header for '%s'. The file does not exist.",
                        $this->pluginFile
                    ),
                    E_USER_WARNING
                );
            }
            return array();
        }

        if ( !function_exists('get_plugin_data') ){
            require_once( ABSPATH . '/wp-admin/includes/plugin.php' );
        }
        return get_plugin_data($this->pluginAbsolutePath, false, false);
    }

    /**
     * Check for plugin updates.
     * The results are stored in the DB option specified in $optionName.
     *
     * @return PluginUpdate|null
     */
    public function checkForUpdates(){
        $installedVersion = $this->getInstalledVersion();
        //Fail silently if we can't find the plugin or read its header.
        if ( $installedVersion === null ) {
            if ( $this->debugMode ) {
                trigger_error(
                    sprintf('Skipping update check for %s - installed version unknown.', $this->pluginFile),
                    E_USER_WARNING
                );
            }
            return null;
        }

        $state = $this->getUpdateState();
        if ( empty($state) ){
            $state = new StdClass;
            $state->lastCheck = 0;
            $state->checkedVersion = '';
            $state->update = null;
        }

        $state->lastCheck = time();
        $state->checkedVersion = $installedVersion;
        $this->setUpdateState($state); //Save before checking in case something goes wrong

        $state->update = $this->requestUpdate();
        $this->setUpdateState($state);

        return $this->getUpdate();
    }

    /**
     * Check for updates if the configured check interval has already elapsed.
     * Will use a shorter check interval on certain admin pages like "Dashboard -> Updates" or when doing cron.
     *
     * You can override the default behaviour by using the "puc_check_now-$slug" filter.
     * The filter callback will be passed three parameters:
     *     - Current decision. TRUE = check updates now, FALSE = don't check now.
     *     - Last check time as a Unix timestamp.
     *     - Configured check period in hours.
     * Return TRUE to check for updates immediately, or FALSE to cancel.
     *
     * This method is declared public because it's a hook callback. Calling it directly is not recommended.
     */
    public function maybeCheckForUpdates(){
        if ( empty($this->checkPeriod) ){
            return;
        }

        $currentFilter = current_filter();
        if ( in_array($currentFilter, array('load-update-core.php', 'upgrader_process_complete')) ) {
            //Check more often when the user visits "Dashboard -> Updates" or does a bulk update.
            $timeout = 60;
        } else if ( in_array($currentFilter, array('load-plugins.php', 'load-update.php')) ) {
            //Also check more often on the "Plugins" page and /wp-admin/update.php.
            $timeout = 3600;
        } else if ( $this->throttleRedundantChecks && ($this->getUpdate() !== null) ) {
            //Check less frequently if it's already known that an update is available.
            $timeout = $this->throttledCheckPeriod * 3600;
        } else if ( defined('DOING_CRON') && constant('DOING_CRON') ) {
            //WordPress cron schedules are not exact, so lets do an update check even
            //if slightly less than $checkPeriod hours have elapsed since the last check.
            $cronFuzziness = 20 * 60;
            $timeout = $this->checkPeriod * 3600 - $cronFuzziness;
        } else {
            $timeout = $this->checkPeriod * 3600;
        }

        $state = $this->getUpdateState();
        $shouldCheck =
            empty($state) ||
            !isset($state->lastCheck) ||
            ( (time() - $state->lastCheck) >= $timeout );

        //Let plugin authors substitute their own algorithm.
        $shouldCheck = apply_filters(
            'puc_check_now-' . $this->slug,
            $shouldCheck,
            (!empty($state) && isset($state->lastCheck)) ? $state->lastCheck : 0,
            $this->checkPeriod
        );

        if ( $shouldCheck ){
            $this->checkForUpdates();
        }
    }

    /**
     * Load the update checker state from the DB.
     *
     * @return StdClass|null
     */
    public function getUpdateState() {
        $state = get_site_option($this->optionName, null);
        if ( empty($state) || !is_object($state)) {
            $state = null;
        }

        if ( !empty($state) && isset($state->update) && is_object($state->update) ){
            $state->update = PluginUpdate_2_0::fromObject($state->update);
        }
        return $state;
    }


    /**
     * Persist the update checker state to the DB.
     *
     * @param StdClass $state
     * @return void
     */
    private function setUpdateState($state) {
        if ( isset($state->update) && is_object($state->update) && method_exists($state->update, 'toStdClass') ) {
            $update = $state->update; /** @var PluginUpdate $update */
            $state->update = $update->toStdClass();
        }
        update_site_option($this->optionName, $state);
    }

    /**
     * Reset update checker state - i.e. last check time, cached update data and so on.
     *
     * Call this when your plugin is being uninstalled, or if you want to
     * clear the update cache.
     */
    public function resetUpdateState() {
        delete_site_option($this->optionName);
    }

    /**
     * Intercept plugins_api() calls that request information about our plugin and
     * use the configured API endpoint to satisfy them.
     *
     * @see plugins_api()
     *
     * @param mixed $result
     * @param string $action
     * @param array|object $args
     * @return mixed
     */
    public function injectInfo($result, $action = null, $args = null){
        $relevant = ($action == 'plugin_information') && isset($args->slug) && (
            ($args->slug == $this->slug) || ($args->slug == dirname($this->pluginFile))
        );
        if ( !$relevant ){
            return $result;
        }

        $pluginInfo = $this->requestInfo();
        $pluginInfo = apply_filters('puc_pre_inject_info-' . $this->slug, $pluginInfo);
        if ($pluginInfo){
            return $pluginInfo->toWpFormat();
        }

        return $result;
    }

    /**
     * Insert the latest update (if any) into the update list maintained by WP.
     *
     * @param StdClass $updates Update list.
     * @return StdClass Modified update list.
     */
    public function injectUpdate($updates){
        //Is there an update to insert?
        $update = $this->getUpdate();

        //No update notifications for mu-plugins unless explicitly enabled. The MU plugin file
        //is usually different from the main plugin file so the update wouldn't show up properly anyway.
        if ( !empty($update) && empty($this->muPluginFile) && $this->isMuPlugin() ) {
            $update = null;
        }

        if ( !empty($update) ) {
            //Let plugins filter the update info before it's passed on to WordPress.
            $update = apply_filters('puc_pre_inject_update-' . $this->slug, $update);
            if ( !is_object($updates) ) {
                $updates = new StdClass();
                $updates->response = array();
            }

            $wpUpdate = $update->toWpFormat();
            $pluginFile = $this->pluginFile;

            if ( $this->isMuPlugin() ) {
                //WP does not support automatic update installation for mu-plugins, but we can still display a notice.
                $wpUpdate->package = null;
                $pluginFile = $this->muPluginFile;
            }
            $updates->response[$pluginFile] = $wpUpdate;

        } else if ( isset($updates, $updates->response) ) {
            unset($updates->response[$this->pluginFile]);
            if ( !empty($this->muPluginFile) ) {
                unset($updates->response[$this->muPluginFile]);
            }
        }

        return $updates;
    }

    /**
     * Rename the update directory to match the existing plugin directory.
     *
     * When WordPress installs a plugin or theme update, it assumes that the ZIP file will contain
     * exactly one directory, and that the directory name will be the same as the directory where
     * the plugin/theme is currently installed.
     *
     * GitHub and other repositories provide ZIP downloads, but they often use directory names like
     * "project-branch" or "project-tag-hash". We need to change the name to the actual plugin folder.
     *
     * @param string $source The directory to copy to /wp-content/plugins. Usually a subdirectory of $remoteSource.
     * @param string $remoteSource WordPress has extracted the update to this directory.
     * @param WP_Upgrader $upgrader
     * @return string|WP_Error
     */
    function fixDirectoryName($source, $remoteSource, $upgrader) {
        global $wp_filesystem; /** @var WP_Filesystem_Base $wp_filesystem */

        //Basic sanity checks.
        if ( !isset($source, $remoteSource, $upgrader, $upgrader->skin, $wp_filesystem) ) {
            return $source;
        }

        //Figure out which plugin is being upgraded.
        $pluginFile = null;
        $skin = $upgrader->skin;
        if ( $skin instanceof Plugin_Upgrader_Skin ) {
            if ( isset($skin->plugin) && is_string($skin->plugin) && ($skin->plugin !== '') ) {
                $pluginFile = $skin->plugin;
            }
        } elseif ( $upgrader->skin instanceof Bulk_Plugin_Upgrader_Skin ) {
            //This case is tricky because Bulk_Plugin_Upgrader_Skin doesn't actually store the plugin
            //filename anywhere. Instead, it has the plugin headers in $plugin_info. So the best we can
            //do is compare those headers to the headers of installed plugins.
            if ( isset($skin->plugin_info) && is_array($skin->plugin_info) ) {
                if ( !function_exists('get_plugins') ){
                    require_once( ABSPATH . '/wp-admin/includes/plugin.php' );
                }

                $installedPlugins = get_plugins();
                $matches = array();
                foreach($installedPlugins as $pluginBasename => $headers) {
                    $diff1 = array_diff_assoc($headers, $skin->plugin_info);
                    $diff2 = array_diff_assoc($skin->plugin_info, $headers);
                    if ( empty($diff1) && empty($diff2) ) {
                        $matches[] = $pluginBasename;
                    }
                }

                //It's possible (though very unlikely) that there could be two plugins with identical
                //headers. In that case, we can't unambiguously identify the plugin that's being upgraded.
                if ( count($matches) !== 1 ) {
                    return $source;
                }

                $pluginFile = reset($matches);
            }
        }

        //If WordPress is upgrading anything other than our plugin, leave the directory name unchanged.
        if ( empty($pluginFile) || ($pluginFile !== $this->pluginFile) ) {
            return $source;
        }

        //Rename the source to match the existing plugin directory.
        $pluginDirectoryName = dirname($this->pluginFile);
        if ( ($pluginDirectoryName === '.') || ($pluginDirectoryName === '/') ) {
            return $source;
        }
        $correctedSource = trailingslashit($remoteSource) . $pluginDirectoryName . '/';
        if ( $source !== $correctedSource ) {
            //The update archive should contain a single directory that contains the rest of plugin files. Otherwise,
            //WordPress will try to copy the entire working directory ($source == $remoteSource). We can't rename
            //$remoteSource because that would break WordPress code that cleans up temporary files after update.
            $sourceFiles = $wp_filesystem->dirlist($remoteSource);
            if ( is_array($sourceFiles) ) {
                $sourceFiles = array_keys($sourceFiles);
                $firstFilePath = trailingslashit($remoteSource) . $sourceFiles[0];

                if ( (count($sourceFiles) > 1) || (!$wp_filesystem->is_dir($firstFilePath)) ) {
                    return new WP_Error(
                        'puc-incorrect-directory-structure',
                        sprintf(
                            'The directory structure of the update is incorrect. All plugin files should be inside ' .
                            'a directory named <span class="code">%s</span>, not at the root of the ZIP file.',
                            htmlentities($this->slug)
                        )
                    );
                }
            }

            $upgrader->skin->feedback(sprintf(
                'Renaming %s to %s&#8230;',
                '<span class="code">' . basename($source) . '</span>',
                '<span class="code">' . $pluginDirectoryName . '</span>'
            ));

            if ( $wp_filesystem->move($source, $correctedSource, true) ) {
                $upgrader->skin->feedback('Plugin directory successfully renamed.');
                return $correctedSource;
            } else {
                return new WP_Error(
                    'puc-rename-failed',
                    'Unable to rename the update to match the existing plugin directory.'
                );
            }
        }

        return $source;
    }


    /**
     * Get the details of the currently available update, if any.
     *
     * If no updates are available, or if the last known update version is below or equal
     * to the currently installed version, this method will return NULL.
     *
     * Uses cached update data. To retrieve update information straight from
     * the metadata URL, call requestUpdate() instead.
     *
     * @return PluginUpdate|null
     */
    public function getUpdate() {
        $state = $this->getUpdateState(); /** @var StdClass $state */

        //Is there an update available insert?
        if ( !empty($state) && isset($state->update) && !empty($state->update) ){
            $update = $state->update;
            //Check if the update is actually newer than the currently installed version.
            $installedVersion = $this->getInstalledVersion();
            if ( ($installedVersion !== null) && version_compare($update->version, $installedVersion, '>') ){
                $update->filename = $this->pluginFile;
                return $update;
            }
        }
        return null;
    }

    /**
     * Add a "Check for updates" link to the plugin row in the "Plugins" page. By default,
     * the new link will appear after the "Visit plugin site" link.
     *
     * You can change the link text by using the "puc_manual_check_link-$slug" filter.
     * Returning an empty string from the filter will disable the link.
     *
     * @param array $pluginMeta Array of meta links.
     * @param string $pluginFile
     * @return array
     */
    public function addCheckForUpdatesLink($pluginMeta, $pluginFile) {
        $isRelevant = ($pluginFile == $this->pluginFile)
                      || (!empty($this->muPluginFile) && $pluginFile == $this->muPluginFile);

        if ( $isRelevant && current_user_can('update_plugins') ) {
            $linkUrl = wp_nonce_url(
                add_query_arg(
                    array(
                        'puc_check_for_updates' => 1,
                        'puc_slug' => $this->slug,
                    ),
                    is_network_admin() ? network_admin_url('plugins.php') : admin_url('plugins.php')
                ),
                'puc_check_for_updates'
            );

            $linkText = apply_filters('puc_manual_check_link-' . $this->slug, 'Check for updates');
            if ( !empty($linkText) ) {
                $pluginMeta[] = sprintf('<a href="%s">%s</a>', esc_attr($linkUrl), $linkText);
            }
        }
        return $pluginMeta;
    }

    /**
     * Check for updates when the user clicks the "Check for updates" link.
     * @see self::addCheckForUpdatesLink()
     *
     * @return void
     */
    public function handleManualCheck() {
        $shouldCheck =
               isset($_GET['puc_check_for_updates'], $_GET['puc_slug'])
            && $_GET['puc_slug'] == $this->slug
            && current_user_can('update_plugins')
            && check_admin_referer('puc_check_for_updates');

        if ( $shouldCheck ) {
            $update = $this->checkForUpdates();
            $status = ($update === null) ? 'no_update' : 'update_available';
            wp_redirect(add_query_arg(
                    array(
                         'puc_update_check_result' => $status,
                         'puc_slug' => $this->slug,
                    ),
                    is_network_admin() ? network_admin_url('plugins.php') : admin_url('plugins.php')
            ));
        }
    }

    /**
     * Display the results of a manual update check.
     * @see self::handleManualCheck()
     *
     * You can change the result message by using the "puc_manual_check_message-$slug" filter.
     */
    public function displayManualCheckResult() {
        if ( isset($_GET['puc_update_check_result'], $_GET['puc_slug']) && ($_GET['puc_slug'] == $this->slug) ) {
            $status = strval($_GET['puc_update_check_result']);
            if ( $status == 'no_update' ) {
                $message = 'This plugin is up to date.';
            } else if ( $status == 'update_available' ) {
                $message = 'A new version of this plugin is available.';
            } else {
                $message = sprintf('Unknown update checker status "%s"', htmlentities($status));
            }
            printf(
                '<div class="updated"><p>%s</p></div>',
                apply_filters('puc_manual_check_message-' . $this->slug, $message, $status)
            );
        }
    }

    /**
     * Check if the plugin file is inside the mu-plugins directory.
     *
     * @return bool
     */
    protected function isMuPlugin() {
        static $cachedResult = null;

        if ( $cachedResult === null ) {
            //Convert both paths to the canonical form before comparison.
            $muPluginDir = realpath(WPMU_PLUGIN_DIR);
            $pluginPath  = realpath($this->pluginAbsolutePath);

            $cachedResult = (strpos($pluginPath, $muPluginDir) === 0);
        }

        return $cachedResult;
    }

    /**
     * Clear the cached plugin version. This method can be set up as a filter (hook) and will
     * return the filter argument unmodified.
     *
     * @param mixed $filterArgument
     * @return mixed
     */
    public function clearCachedVersion($filterArgument = null) {
        $this->cachedInstalledVersion = null;
        return $filterArgument;
    }

    /**
     * Register a callback for filtering query arguments.
     *
     * The callback function should take one argument - an associative array of query arguments.
     * It should return a modified array of query arguments.
     *
     * @uses add_filter() This method is a convenience wrapper for add_filter().
     *
     * @param callable $callback
     * @return void
     */
    public function addQueryArgFilter($callback){
        add_filter('puc_request_info_query_args-'.$this->slug, $callback);
    }

    /**
     * Register a callback for filtering arguments passed to wp_remote_get().
     *
     * The callback function should take one argument - an associative array of arguments -
     * and return a modified array or arguments. See the WP documentation on wp_remote_get()
     * for details on what arguments are available and how they work.
     *
     * @uses add_filter() This method is a convenience wrapper for add_filter().
     *
     * @param callable $callback
     * @return void
     */
    public function addHttpRequestArgFilter($callback){
        add_filter('puc_request_info_options-'.$this->slug, $callback);
    }

    /**
     * Register a callback for filtering the plugin info retrieved from the external API.
     *
     * The callback function should take two arguments. If the plugin info was retrieved
     * successfully, the first argument passed will be an instance of  PluginInfo. Otherwise,
     * it will be NULL. The second argument will be the corresponding return value of
     * wp_remote_get (see WP docs for details).
     *
     * The callback function should return a new or modified instance of PluginInfo or NULL.
     *
     * @uses add_filter() This method is a convenience wrapper for add_filter().
     *
     * @param callable $callback
     * @return void
     */
    public function addResultFilter($callback){
        add_filter('puc_request_info_result-'.$this->slug, $callback, 10, 2);
    }

    /**
     * Register a callback for one of the update checker filters.
     *
     * Identical to add_filter(), except it automatically adds the "puc_" prefix
     * and the "-$plugin_slug" suffix to the filter name. For example, "request_info_result"
     * becomes "puc_request_info_result-your_plugin_slug".
     *
     * @param string $tag
     * @param callable $callback
     * @param int $priority
     * @param int $acceptedArgs
     */
    public function addFilter($tag, $callback, $priority = 10, $acceptedArgs = 1) {
        add_filter('puc_' . $tag . '-' . $this->slug, $callback, $priority, $acceptedArgs);
    }

    /**
     * Initialize the update checker Debug Bar plugin/add-on thingy.
     */
    public function initDebugBarPanel() {
        if ( class_exists('Debug_Bar') ) {
            require_once dirname(__FILE__) . '/debug-bar-plugin.php';
            $this->debugBarPlugin = new PucDebugBarPlugin($this);
        }
    }
}

endif;

if ( !class_exists('PluginInfo_2_0') ):

/**
 * A container class for holding and transforming various plugin metadata.
 *
 * @author Janis Elsts
 * @copyright 2015
 * @version 2.0
 * @access public
 */
class PluginInfo_2_0 {
    //Most fields map directly to the contents of the plugin's info.json file.
    //See the relevant docs for a description of their meaning.
    public $name;
    public $slug;
    public $version;
    public $homepage;
    public $sections;
    public $banners;
    public $download_url;

    public $author;
    public $author_homepage;

    public $requires;
    public $tested;
    public $upgrade_notice;

    public $rating;
    public $num_ratings;
    public $downloaded;
    public $last_updated;

    public $id = 0; //The native WP.org API returns numeric plugin IDs, but they're not used for anything.

    public $filename; //Plugin filename relative to the plugins directory.

    /**
     * Create a new instance of PluginInfo from JSON-encoded plugin info
     * returned by an external update API.
     *
     * @param string $json Valid JSON string representing plugin info.
     * @param bool $triggerErrors
     * @return PluginInfo|null New instance of PluginInfo, or NULL on error.
     */
    public static function fromJson($json, $triggerErrors = false){
        /** @var StdClass $apiResponse */
        $apiResponse = json_decode($json);
        if ( empty($apiResponse) || !is_object($apiResponse) ){
            if ( $triggerErrors ) {
                trigger_error(
                    "Failed to parse plugin metadata. Try validating your .json file with http://jsonlint.com/",
                    E_USER_NOTICE
                );
            }
            return null;
        }

        //Very, very basic validation.
        $valid = isset($apiResponse->name) && !empty($apiResponse->name) && isset($apiResponse->version) && !empty($apiResponse->version);
        if ( !$valid ){
            if ( $triggerErrors ) {
                trigger_error(
                    "The plugin metadata file does not contain the required 'name' and/or 'version' keys.",
                    E_USER_NOTICE
                );
            }
            return null;
        }

        $info = new self();
        foreach(get_object_vars($apiResponse) as $key => $value){
            $info->$key = $value;
        }

        return $info;
    }

    /**
     * Transform plugin info into the format used by the native WordPress.org API
     *
     * @return object
     */
    public function toWpFormat(){
        $info = new StdClass;

        //The custom update API is built so that many fields have the same name and format
        //as those returned by the native WordPress.org API. These can be assigned directly.
        $sameFormat = array(
            'name', 'slug', 'version', 'requires', 'tested', 'rating', 'upgrade_notice',
            'num_ratings', 'downloaded', 'homepage', 'last_updated',
        );
        foreach($sameFormat as $field){
            if ( isset($this->$field) ) {
                $info->$field = $this->$field;
            } else {
                $info->$field = null;
            }
        }

        //Other fields need to be renamed and/or transformed.
        $info->download_link = $this->download_url;

        if ( !empty($this->author_homepage) ){
            $info->author = sprintf('<a href="%s">%s</a>', $this->author_homepage, $this->author);
        } else {
            $info->author = $this->author;
        }

        if ( is_object($this->sections) ){
            $info->sections = get_object_vars($this->sections);
        } elseif ( is_array($this->sections) ) {
            $info->sections = $this->sections;
        } else {
            $info->sections = array('description' => '');
        }

        if ( !empty($this->banners) ) {
            //WP expects an array with two keys: "high" and "low". Both are optional.
            //Docs: https://wordpress.org/plugins/about/faq/#banners
            $info->banners = is_object($this->banners) ? get_object_vars($this->banners) : $this->banners;
            $info->banners = array_intersect_key($info->banners, array('high' => true, 'low' => true));
        }

        return $info;
    }
}

endif;

if ( !class_exists('PluginUpdate_2_0') ):

/**
 * A simple container class for holding information about an available update.
 *
 * @author Janis Elsts
 * @copyright 2015
 * @version 2.0
 * @access public
 */
class PluginUpdate_2_0 {
    public $id = 0;
    public $slug;
    public $version;
    public $homepage;
    public $download_url;
    public $upgrade_notice;
    public $filename; //Plugin filename relative to the plugins directory.

    private static $fields = array('id', 'slug', 'version', 'homepage', 'download_url', 'upgrade_notice', 'filename');

    /**
     * Create a new instance of PluginUpdate from its JSON-encoded representation.
     *
     * @param string $json
     * @param bool $triggerErrors
     * @return PluginUpdate|null
     */
    public static function fromJson($json, $triggerErrors = false){
        //Since update-related information is simply a subset of the full plugin info,
        //we can parse the update JSON as if it was a plugin info string, then copy over
        //the parts that we care about.
        $pluginInfo = PluginInfo_2_0::fromJson($json, $triggerErrors);
        if ( $pluginInfo != null ) {
            return self::fromPluginInfo($pluginInfo);
        } else {
            return null;
        }
    }

    /**
     * Create a new instance of PluginUpdate based on an instance of PluginInfo.
     * Basically, this just copies a subset of fields from one object to another.
     *
     * @param PluginInfo $info
     * @return PluginUpdate
     */
    public static function fromPluginInfo($info){
        return self::fromObject($info);
    }

    /**
     * Create a new instance of PluginUpdate by copying the necessary fields from
     * another object.
     *
     * @param StdClass|PluginInfo|PluginUpdate $object The source object.
     * @return PluginUpdate The new copy.
     */
    public static function fromObject($object) {
        $update = new self();
        $fields = self::$fields;
        if (!empty($object->slug)) $fields = apply_filters('puc_retain_fields-'.$object->slug, $fields);
        foreach($fields as $field){
            if (property_exists($object, $field)) {
                $update->$field = $object->$field;
            }
        }
        return $update;
    }

    /**
     * Create an instance of StdClass that can later be converted back to
     * a PluginUpdate. Useful for serialization and caching, as it avoids
     * the "incomplete object" problem if the cached value is loaded before
     * this class.
     *
     * @return StdClass
     */
    public function toStdClass() {
        $object = new StdClass();
        $fields = self::$fields;
        if (!empty($this->slug)) $fields = apply_filters('puc_retain_fields-'.$this->slug, $fields);
        foreach($fields as $field){
            if (property_exists($this, $field)) {
                $object->$field = $this->$field;
            }
        }
        return $object;
    }


    /**
     * Transform the update into the format used by WordPress native plugin API.
     *
     * @return object
     */
    public function toWpFormat(){
        $update = new StdClass;

        $update->id = $this->id;
        $update->slug = $this->slug;
        $update->new_version = $this->version;
        $update->url = $this->homepage;
        $update->package = $this->download_url;
        $update->plugin = $this->filename;

        if ( !empty($this->upgrade_notice) ){
            $update->upgrade_notice = $this->upgrade_notice;
        }

        return $update;
    }
}

endif;

if ( !class_exists('PucFactory') ):

/**
 * A factory that builds instances of other classes from this library.
 *
 * When multiple versions of the same class have been loaded (e.g. PluginUpdateChecker 1.2
 * and 1.3), this factory will always use the latest available version. Register class
 * versions by calling {@link PucFactory::addVersion()}.
 *
 * At the moment it can only build instances of the PluginUpdateChecker class. Other classes
 * are intended mainly for internal use and refer directly to specific implementations. If you
 * want to instantiate one of them anyway, you can use {@link PucFactory::getLatestClassVersion()}
 * to get the class name and then create it with <code>new $class(...)</code>.
 */
class PucFactory {
    protected static $classVersions = array();
    protected static $sorted = false;

    /**
     * Create a new instance of PluginUpdateChecker.
     *
     * @see PluginUpdateChecker::__construct()
     *
     * @param $metadataUrl
     * @param $pluginFile
     * @param string $slug
     * @param int $checkPeriod
     * @param string $optionName
     * @param string $muPluginFile
     * @return PluginUpdateChecker
     */
    public static function buildUpdateChecker($metadataUrl, $pluginFile, $slug = '', $checkPeriod = 12, $optionName = '', $muPluginFile = '') {
        $class = self::getLatestClassVersion('PluginUpdateChecker');
        return new $class($metadataUrl, $pluginFile, $slug, $checkPeriod, $optionName, $muPluginFile);
    }

    /**
     * Get the specific class name for the latest available version of a class.
     *
     * @param string $class
     * @return string|null
     */
    public static function getLatestClassVersion($class) {
        if ( !self::$sorted ) {
            self::sortVersions();
        }

        if ( isset(self::$classVersions[$class]) ) {
            return reset(self::$classVersions[$class]);
        } else {
            return null;
        }
    }

    /**
     * Sort available class versions in descending order (i.e. newest first).
     */
    protected static function sortVersions() {
        foreach ( self::$classVersions as $class => $versions ) {
            uksort($versions, array(__CLASS__, 'compareVersions'));
            self::$classVersions[$class] = $versions;
        }
        self::$sorted = true;
    }

    protected static function compareVersions($a, $b) {
        return -version_compare($a, $b);
    }

    /**
     * Register a version of a class.
     *
     * @access private This method is only for internal use by the library.
     *
     * @param string $generalClass Class name without version numbers, e.g. 'PluginUpdateChecker'.
     * @param string $versionedClass Actual class name, e.g. 'PluginUpdateChecker_1_2'.
     * @param string $version Version number, e.g. '1.2'.
     */
    public static function addVersion($generalClass, $versionedClass, $version) {
        if ( !isset(self::$classVersions[$generalClass]) ) {
            self::$classVersions[$generalClass] = array();
        }
        self::$classVersions[$generalClass][$version] = $versionedClass;
        self::$sorted = false;
    }
}

endif;

// require_once(dirname(__FILE__) . '/github-checker.php');

//Register classes defined in this file with the factory.
PucFactory::addVersion('PluginUpdateChecker', 'PluginUpdateChecker_2_0', '2.0');
PucFactory::addVersion('PluginUpdate', 'PluginUpdate_2_0', '2.0');
PucFactory::addVersion('PluginInfo', 'PluginInfo_2_0', '2.0');
// PucFactory::addVersion('PucGitHubChecker', 'PucGitHubChecker_2_0', '2.0');

/**
 * Create non-versioned variants of the update checker classes. This allows for backwards
 * compatibility with versions that did not use a factory, and it simplifies doc-comments.
 */
if ( !class_exists('PluginUpdateChecker') ) {
    class PluginUpdateChecker extends PluginUpdateChecker_2_0 { }
}

if ( !class_exists('PluginUpdate') ) {
    class PluginUpdate extends PluginUpdate_2_0 {}
}

if ( !class_exists('PluginInfo') ) {
    class PluginInfo extends PluginInfo_2_0 {}
}