UsageStatsPlugin.inc.php

<?php

/**
 * @file plugins/generic/usageStats/UsageStatsPlugin.inc.php
 *
 * Copyright (c) 2013-2020 Simon Fraser University
 * Copyright (c) 2003-2020 John Willinsky
 * Distributed under the GNU GPL v3. For full terms see the file docs/COPYING.
 *
 * @class UsageStatsPlugin
 * @ingroup plugins_generic_usageStats
 *
 * @brief Provide usage statistics to data objects.
 */

use PKP\plugins\GenericPlugin;
use PKP\core\JSONMessage;
use PKP\file\PrivateFileManager;
use PKP\linkAction\request\AjaxModal;
use PKP\linkAction\LinkAction;
use PKP\notification\PKPNotification;
use PKP\statistics\PKPStatisticsHelper;
use PKP\core\PKPApplication;
use PKP\plugins\HookRegistry;
use PKP\plugins\PluginRegistry;

use APP\submission\Submission;
use APP\notification\NotificationManager;
use APP\core\Application;

class UsageStatsPlugin extends GenericPlugin {

	/** @var $_currentUsageEvent array */
	var $_currentUsageEvent;

	/** @var $_dataPrivacyOn boolean */
	var $_dataPrivacyOn;

	/** @var $_optedOut boolean */
	var $_optedOut;

	/** @var $_saltpath string */
	var $_saltpath;

	/**
	 * Constructor.
	 */
	function __construct() {
		parent::__construct();

		// The upgrade and install processes will need access
		// to constants defined in that report plugin.
		$application = Application::get();
		$applicationName = $application->getName();
		switch ($applicationName) {
			case 'ojs2':
				import('plugins.generic.usageStats.OJSUsageStatsReportPlugin');
				break;
			case 'omp':
				import('plugins.generic.usageStats.OMPUsageStatsReportPlugin');
				break;
			case 'ops':
				import('plugins.generic.usageStats.OPSUsageStatsReportPlugin');
				break;
		}
	}


	//
	// Public methods.
	//
	/**
	 * Determine whether the plugin can be enabled.
	 *
	 * Can only be enabled or disabled at the site-wide level.
	 *
	 * @return boolean
	 */
	function getCanEnable() {
		return !((bool) Application::get()->getRequest()->getContext());
	}

	/**
	 * Determine whether the plugin can be disabled.
	 *
	 * Can only be enabled or disabled at the site-wide level.
	 *
	 * @return boolean
	 */
	function getCanDisable() {
		return !((bool) Application::get()->getRequest()->getContext());
	}

	/**
	 * Get the report plugin object that implements
	 * the metric type details.
	 * @return UsageStatsReportPlugin
	 */
	function getReportPlugin() {
		$application = Application::get();
		$applicationName = $application->getName();
		switch ($applicationName) {
			case 'ojs2':
				$this->import('OJSUsageStatsReportPlugin');
				return new OJSUsageStatsReportPlugin();
			case 'omp':
				$this->import('OMPUsageStatsReportPlugin');
				return new OMPUsageStatsReportPlugin();
			case 'ops':
				$this->import('OPSUsageStatsReportPlugin');
				return new OPSUsageStatsReportPlugin();
			default:
				assert(false);
		}
	}


	//
	// Implement methods from Plugin.
	//
	/**
	 * @copydoc Plugin::register()
	 */
	function register($category, $path, $mainContextId = null) {
		$success = parent::register($category, $path, $mainContextId);

		HookRegistry::register('AcronPlugin::parseCronTab', array($this, 'callbackParseCronTab'));

		if ($this->getEnabled($mainContextId) && $success) {

			$this->_dataPrivacyOn = $this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'dataPrivacyOption');
			$this->_saltpath = $this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'saltFilepath');
			// Check config for backward compatibility.
			if (!$this->_saltpath) $this->_saltpath = Config::getVar('usageStats', 'salt_filepath');
			$request = Application::get()->getRequest();
			$this->_optedOut = $request->getCookieVar('usageStats-opt-out');
			if ($this->_optedOut) {
				// Renew the Opt-Out cookie if present.
				$request->setCookieVar('usageStats-opt-out', true, time() + 60*60*24*365);
			}

			if ($this->_dataPrivacyOn) {
				$this->import('UsageStatsOptoutBlockPlugin');
				PluginRegistry::register('blocks', new UsageStatsOptoutBlockPlugin($this), $this->getPluginPath());
			}

			PluginRegistry::register('reports', $this->getReportPlugin(), $this->getPluginPath());

			// Register callbacks.
			HookRegistry::register('LoadHandler', array($this, 'callbackLoadHandler'));

			// If the plugin will provide the access logs,
			// register to the usage event hook provider.
			if ($this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'createLogFiles')) {
				HookRegistry::register('UsageEventPlugin::getUsageEvent', array(&$this, 'logUsageEvent'));
			}

			$this->_registerTemplateResource(true);

			$this->displayReaderStatistics();
		}

		return $success;
	}

	/**
	 * Register assets and output hooks to display statistics on the reader
	 * frontend.
	 *
	 * @return null
	 */
	function displayReaderStatistics() {
		$application = Application::get();
		$applicationName = $application->getName();
		switch($applicationName) {
			case 'ojs2':
			// Add chart to article view page
			HookRegistry::register('Templates::Article::Main', array($this, 'displayReaderArticleGraph'));
				break;
			case 'omp':
				// Add chart to book view page
				HookRegistry::register('Templates::Catalog::Book::Main', array($this, 'displayReaderMonographGraph'));
				break;
			case 'ops':
				// Add chart to preprint view page
				HookRegistry::register('Templates::Preprint::Main', array($this, 'displayReaderPreprintGraph'));
				break;
			default:
				assert(false);
		}
	}

	/**
	 * Get the path to the salt file.
	 * @return string
	 */
	function getSaltpath() {
		return $this->_saltpath;
	}

	/**
	 * @copydoc Plugin::getDisplayName()
	 */
	function getDisplayName() {
		return __('plugins.generic.usageStats.displayName');
	}

	/**
	 * @copydoc Plugin::getDescription()
	 */
	function getDescription() {
		return __('plugins.generic.usageStats.description');
	}

	/**
	 * @copydoc Plugin::isSitePlugin()
	 */
	function isSitePlugin() {
		return true;
	}

	/**
	 * @copydoc Plugin::getInstallSitePluginSettingsFile()
	 */
	function getInstallSitePluginSettingsFile() {
		return $this->getPluginPath() . DIRECTORY_SEPARATOR . 'settings.xml';
	}

	/**
	 * @copydoc Plugin::getInstallMigration()
	 */
	function getInstallMigration() {
		$this->import('UsageStatsMigration');
		return new UsageStatsMigration();
	}

	/**
	 * @copydoc Plugin::manage()
	 */
	function manage($args, $request) {
		$singleContextSite = (Services::get('context')->getCount() == 1);
		if ($request->getContext() && !$singleContextSite) {
			$this->import('UsageStatsSettingsForm');
			$settingsForm = new UsageStatsSettingsForm($this);
		} else {
			$this->import('UsageStatsSiteSettingsForm');
			$settingsForm = new UsageStatsSiteSettingsForm($this);
		}
		switch($request->getUserVar('verb')) {
			case 'settings':
				$settingsForm->initData();
				return new JSONMessage(true, $settingsForm->fetch($request));
			case 'save':
				$settingsForm->readInputData();
				if ($settingsForm->validate()) {
					$settingsForm->execute();
					$notificationManager = new NotificationManager();
					$notificationManager->createTrivialNotification(
						$request->getUser()->getId(),
						PKPNotification::NOTIFICATION_TYPE_SUCCESS,
						array('contents' => __('plugins.generic.usageStats.settings.saved'))
					);
					return new JSONMessage(true);
				}
				return new JSONMessage(true, $settingsForm->fetch($request));
		}
		return parent::manage($args, $request);
	}


	//
	// Implement template methods from GenericPlugin.
	//
	/**
	 * @copydoc Plugin::getActions()
	 */
	function getActions($request, $verb) {
		$router = $request->getRouter();
		return array_merge(
			$this->getEnabled()?array(
				new LinkAction(
					'settings',
					new AjaxModal(
						$router->url($request, null, null, 'manage', null, array('verb' => 'settings', 'plugin' => $this->getName(), 'category' => 'generic')),
						$this->getDisplayName()
					),
					__('manager.plugins.settings'),
					null
				),
			):array(),
			parent::getActions($request, $verb)
		);
	}


	//
	// Hook implementations.
	//
	/**
 	 * @see PKPPageRouter::route()
 	 * @param $hookName string
 	 * @param $args array [
	 *  @option string page
	 *  @option string op
	 *  @option string handler file
	 * ]
 	 *
	 */
	function callbackLoadHandler($hookName, $args) {
		// Check the page.
		$page = $args[0];
		if ($page !== 'usageStats') return;
		// Check the operation.
		$availableOps = array('privacyInformation');
		$op = $args[1];
		if (!in_array($op, $availableOps)) return;
		// The handler had been requested.
		define('HANDLER_CLASS', 'UsageStatsHandler');
		define('USAGESTATS_PLUGIN_NAME', $this->getName());
		$handlerFile =& $args[2];
		$handlerFile = $this->getPluginPath() . '/' . 'UsageStatsHandler.inc.php';
	}

	/**
	 * @see AcronPlugin::parseCronTab()
	 * @param $hookName string
 	 * @param $args array [
	 *  @option array Task files paths
	 * ]
	 * @return bolean
	 */
	function callbackParseCronTab($hookName, $args) {
		if ($this->getEnabled() || !Application::isInstalled()) {
			$taskFilesPath =& $args[0]; // Reference needed.
			$taskFilesPath[] = $this->getPluginPath() . DIRECTORY_SEPARATOR . 'scheduledTasksAutoStage.xml';
		}
		return false;
	}

	/**
	 * Validate that the path of the salt file exists and is writable.
	 * @param $saltpath string
	 * @return boolean
	 */
	function validateSaltpath($saltpath) {
		if (!file_exists($saltpath)) {
			touch($saltpath);
		}
		if (is_writable($saltpath)) {
			return true;
		}
		return false;
	}

	/**
	 * Get all hooks that define the
	 * finished file download.
	 * @return array
	 */
	protected function getDownloadFinishedEventHooks() {
		$hooks = array('FileManager::downloadFileFinished');
		$application = Application::get();
		$applicationName = $application->getName();
		switch ($applicationName) {
			case 'ojs2':
				$hooks[] = 'HtmlArticleGalleyPlugin::articleDownloadFinished';
				$hooks[] = 'LensGalleyPlugin::articleDownloadFinished';
				break;
			case 'omp':
				$hooks[] = 'HtmlMonographFilePlugin::monographDownloadFinished';
				break;
			case 'ops':
				$hooks[] = 'HtmlArticleGalleyPlugin::articleDownloadFinished';
				break;
		}
		return $hooks;
	}

	/**
	 * Log the usage event into a file.
	 * @param $hookName string
	 * @param $args array [
	 *  @option string hook name
	 *  @option array usage event = compact(
	 *		'time', 'pubObject', 'assocType', 'canonicalUrl', 'mimeType',
	 *		'identifiers', 'downloadSuccess', 'serviceUri',
	 *		'ip', 'host', 'user', 'roles', 'userAgent', 'referrer',
	 *		'classification')
	 * ]
	 * @return boolean
	 */
	function logUsageEvent($hookName, $args) {
		$hookName = $args[0];
		$usageEvent = $args[1];

		// Check the statistics opt-out.
		if ($this->_optedOut) return false;

		if (in_array($hookName, $this->getDownloadFinishedEventHooks()) && !$usageEvent && $this->_currentUsageEvent) {
			// File download is finished, try to log the current usage event.
			$downloadSuccess = $args[2];
			if ($downloadSuccess && !connection_aborted()) {
				$this->_currentUsageEvent['downloadSuccess'] = true;
				$usageEvent = $this->_currentUsageEvent;
			}
		}

		if ($usageEvent && !$usageEvent['downloadSuccess']) {
			// Don't log until we get the download finished hook call.
			$this->_currentUsageEvent = $usageEvent;
			return false;
		}

		if ($usageEvent) {
			$this->_writeUsageEventInLogFile($usageEvent);
		}

		return false;
	}

	/**
	 * Get the geolocation tool to process geo localization
	 * data.
	 * @return mixed GeoLocationTool object or null
	 */
	function &getGeoLocationTool() {
		/** Geo location tool wrapper class. If changing the geo location tool
		* is required, change the code inside this class, keeping the public
		* interface. */
		$this->import('GeoLocationTool');

		$null = null;
		$tool = new GeoLocationTool();
		if ($tool->isPresent()) {
			return $tool;
		} else {
			return $null;
		}
	}

	/**
	 * Get the plugin's files path.
	 * @return string
	 */
	function getFilesPath() {
		$fileMgr = new PrivateFileManager();

		return realpath($fileMgr->getBasePath()) . DIRECTORY_SEPARATOR . 'usageStats';
	}

	/**
	 * Get the plugin's usage event logs path.
	 * @return string
	 */
	function getUsageEventLogsPath() {
		return $this->getFilesPath() . DIRECTORY_SEPARATOR . 'usageEventLogs';
	}

	/**
	 * Get current day usage event log name.
	 * @return string
	 */
	function getUsageEventCurrentDayLogName() {
		return 'usage_events_' . date("Ymd") . '.log';
	}

	/**
	 * Load the JavaScript assets and pass data to the scripts
	 *
	 * @param $contexts string|array Contexts in which to load the scripts.
	 * @return null
	 */
	function loadJavascript($contexts) {

		$request = Application::get()->getRequest();
		$templateMgr = TemplateManager::getManager($request);

		// Register Chart.js on the frontend article view
		$templateMgr->addJavaScript(
			'chartJS',
			'https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.0.1/Chart.js',
			array(
				'contexts' => $contexts,
			)
		);

		// Add locale and configuration data
		$context = $request->getContext();
		$chartType = $this->_getPluginSetting($context, 'chartType');
		$script_data = 'var pkpUsageStats = pkpUsageStats || {};';
		$script_data .= 'pkpUsageStats.locale = pkpUsageStats.locale || {};';
		$script_data .= 'pkpUsageStats.locale.months = ' . json_encode(explode(' ', __('plugins.generic.usageStats.monthInitials'))) . ';';
		$script_data .= 'pkpUsageStats.config = pkpUsageStats.config || {};';
		$script_data .= 'pkpUsageStats.config.chartType = ' . json_encode($chartType) . ';';
		$templateMgr->addJavaScript(
			'pkpUsageStatsConfig',
			$script_data,
			array(
				'inline' => true,
				'contexts' => $contexts,
			)
		);

		// Register the JS which initializes the chart
		$baseImportPath = $request->getBaseUrl() . DIRECTORY_SEPARATOR . $this->getPluginPath() . DIRECTORY_SEPARATOR;
		$templateMgr->addJavaScript(
			'usageStatsFrontend',
			$baseImportPath . 'js/UsageStatsFrontendHandler.js',
			array(
				'contexts' => $contexts,
			)
		);
	}

	/**
	 * Add a data set to the script data output
	 *
	 * @param $data array JS data to pass to the scripts
	 * @param $pubObjectType string The type of object this data is for
	 * @param $pubObjectId string The id of the object this data is for
	 * @param $contexts string|array Contexts in which to load the scripts.
	 * @return null
	 */
	function addJavascriptData($data, $pubObjectType, $pubObjectId, $contexts) {

		// Initialize the name space
		$script_data = 'var pkpUsageStats = pkpUsageStats || {};';
		$script_data .= 'pkpUsageStats.data = pkpUsageStats.data || {};';
		$script_data .= 'pkpUsageStats.data.' . $pubObjectType . ' = pkpUsageStats.data.' . $pubObjectType . ' || {};';
		$namespace = $pubObjectType . '[' . $pubObjectId . ']';
		$script_data .= 'pkpUsageStats.data.' . $namespace . ' = ' . json_encode($data) .';';

		// Register the data
		$request = Application::get()->getRequest();
		$templateMgr = TemplateManager::getManager($request);
		$templateMgr->addJavaScript(
			'pkpUsageStatsData',
			$script_data,
			array(
				'inline' => true,
				'contexts' => $contexts,
			)
		);
	}

	/**
	 * Fetch a template with the requested params
	 *
	 * @param $args array Variables to assign to the template
	 * @param $template string Template file name
	 * @param $smarty object Smarty template object
	 * @return string
	 */
	function getTemplate($args, $template, $smarty) {
		$smarty->assign($args);
		return $smarty->fetch($this->getTemplateResource($template));
	}

	/**
	 * Add chart to article view page
	 *
	 * Hooked to `Templates::Article::Main`
	 * @param $hookName string
	 * @param $params array [
	 *  @option Smarty
	 *  @option string HTML output to return
	 * ]
	 */
	function displayReaderArticleGraph($hookName, $params) {
		$smarty =& $params[1];
		$output =& $params[2];

		$context = $smarty->getTemplateVars('currentContext');
		$pluginSettingsDao = DAORegistry::getDAO('PluginSettingsDAO');
		$contextDisplaySettingExists = $pluginSettingsDao->settingExists($context->getId(), $this->getName(), 'displayStatistics');
		$contextDisplaySetting = $this->getSetting($context->getId(), 'displayStatistics');
		$siteDisplaySetting = $this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'displayStatistics');
		if (($contextDisplaySettingExists && $contextDisplaySetting) ||
			(!$contextDisplaySettingExists && $siteDisplaySetting)) {

				$pubObject = $smarty->getTemplateVars('article');
				assert($pubObject instanceof Submission);
				$pubObjectId = $pubObject->getId();
				$pubObjectType = 'Submission';

				$output .= $this->getTemplate(
					array(
						'pubObjectType' => $pubObjectType,
						'pubObjectId'   => $pubObjectId,
					),
					'outputFrontend.tpl',
					$smarty
				);

				$this->addJavascriptData($this->getAllDownloadsStats($pubObjectId), $pubObjectType, $pubObjectId, 'frontend-article-view');
				$this->loadJavascript('frontend-article-view' );
		}
		return false;
	}

	/**
	 * Add chart to book view page
	 *
	 * Hooked to `Templates::Catalog::Book::Main`
	 * @param $hookName string
	 * @param $params arrayarray [
	 *  @option Smarty
	 *  @option string HTML output to return
	 * ]
	 */
	function displayReaderMonographGraph($hookName, $params) {
		$smarty =& $params[1];
		$output =& $params[2];

		$context = $smarty->getTemplateVars('currentContext');
		$pluginSettingsDao = DAORegistry::getDAO('PluginSettingsDAO');
		$contextDisplaySettingExists = $pluginSettingsDao->settingExists($context->getId(), $this->getName(), 'displayStatistics');
		$contextDisplaySetting = $this->getSetting($context->getId(), 'displayStatistics');
		$siteDisplaySetting = $this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'displayStatistics');
		if (($contextDisplaySettingExists && $contextDisplaySetting) ||
			(!$contextDisplaySettingExists && $siteDisplaySetting)) {

				$pubObject = $smarty->getTemplateVars('publishedSubmission');
				assert($pubObject instanceof Submission);
				$pubObjectId = $pubObject->getId();
				$pubObjectType = 'Submission';

				$output .= $this->getTemplate(
					array(
						'pubObjectType' => $pubObjectType,
						'pubObjectId'   => $pubObjectId,
					),
					'outputFrontend.tpl',
					$smarty
				);

				$this->addJavascriptData($this->getAllDownloadsStats($pubObjectId), $pubObjectType, $pubObjectId, 'frontend-catalog-book');
				$this->loadJavascript('frontend-catalog-book' );
		}
		return false;
	}

	/**
	 * Add chart to preprint view page
	 *
	 * Hooked to `Templates::Preprint::Main`
	 * @param $hookName string
	 * @param $params array [
	 *  @option Smarty
	 *  @option string HTML output to return
	 * ]
	 */
	function displayReaderPreprintGraph($hookName, $params) {
		$smarty =& $params[1];
		$output =& $params[2];

		$context = $smarty->getTemplateVars('currentContext');
		$pluginSettingsDao = DAORegistry::getDAO('PluginSettingsDAO');
		$contextDisplaySettingExists = $pluginSettingsDao->settingExists($context->getId(), $this->getName(), 'displayStatistics');
		$contextDisplaySetting = $this->getSetting($context->getId(), 'displayStatistics');
		$siteDisplaySetting = $this->getSetting(PKPApplication::CONTEXT_ID_NONE, 'displayStatistics');
		if (($contextDisplaySettingExists && $contextDisplaySetting) ||
			(!$contextDisplaySettingExists && $siteDisplaySetting)) {

				$pubObject = $smarty->getTemplateVars('preprint');
				assert($pubObject instanceof Submission);
				$pubObjectId = $pubObject->getId();
				$pubObjectType = 'Submission';

				$output .= $this->getTemplate(
					array(
						'pubObjectType' => $pubObjectType,
						'pubObjectId'   => $pubObjectId,
					),
					'outputFrontend.tpl',
					$smarty
				);

				$this->addJavascriptData($this->getAllDownloadsStats($pubObjectId), $pubObjectType, $pubObjectId, 'frontend-preprint-view');
				$this->loadJavascript('frontend-preprint-view' );
		}
		return false;
	}


	//
	// Private helper methods.
	//
	/**
	 * @param $usageEvent array = compact(
	 *		'time', 'pubObject', 'assocType', 'canonicalUrl', 'mimeType',
	 *		'identifiers', 'downloadSuccess', 'serviceUri',
	 *		'ip', 'host', 'user', 'roles', 'userAgent', 'referrer',
	 *		'classification')
	 */
	function _writeUsageEventInLogFile($usageEvent) {
		$salt = null;
		if ($this->_dataPrivacyOn) {
			// Salt management.
			$saltFilename = $this->getSaltpath();
			if (!$this->validateSaltpath($saltFilename)) return false;
			$currentDate = date("Ymd");
			$saltFilenameLastModified = date("Ymd", filemtime($saltFilename));
			$file = fopen($saltFilename, 'r');
			$salt = trim(fread($file,filesize($saltFilename)));
			fclose($file);
			if (empty($salt) || ($currentDate != $saltFilenameLastModified)) {
				if(function_exists('mcrypt_create_iv')) {
					$newSalt = bin2hex(mcrypt_create_iv(16, MCRYPT_DEV_URANDOM|MCRYPT_RAND));
				} elseif (function_exists('openssl_random_pseudo_bytes')){
					$newSalt = bin2hex(openssl_random_pseudo_bytes(16, $cstrong));
				} elseif (file_exists('/dev/urandom')){
					$newSalt = bin2hex(file_get_contents('/dev/urandom', false, null, 0, 16));
				} else {
					$newSalt = mt_rand();
				}
				$file = fopen($saltFilename,'wb');
				if (flock($file, LOCK_EX)) {
					fwrite($file, $newSalt);
					flock($file, LOCK_UN);
				} else {
					assert(false);
				}
				fclose($file);
				$salt = $newSalt;
			}
		}

		// Manage the IP address (evtually hash it)
		if ($this->_dataPrivacyOn) {
			if (!isset($salt)) return false;
			// Hash the IP
			$hashedIp = $this->_hashIp($usageEvent['ip'], $salt);
			// Never store unhashed IPs!
			if ($hashedIp === false) return false;
			$desiredParams = array($hashedIp);
		} else {
			$desiredParams = array($usageEvent['ip']);
		}

		if (isset($usageEvent['classification'])) {
			$desiredParams[] = $usageEvent['classification'];
		} else {
			$desiredParams[] = '-';
		}

		if (!$this->_dataPrivacyOn && isset($usageEvent['user'])) {
			$desiredParams[] = $usageEvent['user']->getId();
		} else {
			$desiredParams[] = '-';
		}

		$desiredParams = array_merge($desiredParams,
		array('"' . $usageEvent['time'] . '"', $usageEvent['canonicalUrl'],
						'200', // The usage event plugin always log requests that returned this code.
						'"' . $usageEvent['userAgent'] . '"'));

		$usageLogEntry = implode(' ', $desiredParams) . PHP_EOL;

		$fileMgr = new PrivateFileManager();

		// Get the current day filename.
		$filename = $this->getUsageEventCurrentDayLogName();

		// Check the plugin file directory.
		$usageEventFilesPath = $this->getUsageEventLogsPath();
		if (!$fileMgr->fileExists($usageEventFilesPath, 'dir')) {
			$success = $fileMgr->mkdirtree($usageEventFilesPath);
			if (!$success) {
				// Files directory wrong configuration?
				assert(false);
				return false;
			}
		}

		$filePath = $usageEventFilesPath . DIRECTORY_SEPARATOR . $filename;
		$fp = fopen($filePath, 'ab');
		if (flock($fp, LOCK_EX)) {
			fwrite($fp, $usageLogEntry);
			flock($fp, LOCK_UN);
		} else {
			// Couldn't lock the file.
			assert(false);
		}
		fclose($fp);
	}

	/**
	* Hash (SHA256) the given IP using the given SALT.
	*
	* NB: This implementation was taken from OA-S directly. See
	* http://sourceforge.net/p/openaccessstati/code-0/3/tree/trunk/logfile-parser/lib/logutils.php
	*
	* @param $ip string
	* @param $salt string
	* @return string|boolean The hashed IP or boolean false if something went wrong.
	*/
	function _hashIp($ip, $salt) {
		if(function_exists('mhash')) {
			return bin2hex(mhash(MHASH_SHA256, $ip.$salt));
		} else {
			assert(function_exists('hash'));
			if (!function_exists('hash')) return false;
			return hash('sha256', $ip.$salt);
		}
	}

	/**
	 * Get prepared download statistics from the DB
	 * @param $pubObjectId integer
	 * @return array
	 */
	function _getDownloadStats($pubObjectId) {
		$cache = CacheManager::getManager()->getCache('downloadStats', $pubObjectId, array($this, '_downloadStatsCacheMiss'));
		if (time() - $cache->getCacheTime() > 60 * 60 * 24) {
			// Cache is older than one day, erase it.
			$cache->flush();
		}
		$statsReports = $cache->get($pubObjectId);

		$currentYear = date("Y");
		$months = range(1, 12);
		$statsByFormat = $statsByMonth = $years = array();
		$totalDownloads = 0;
		foreach ($statsReports as $statsReport) {
			$month = (int) substr($statsReport[PKPStatisticsHelper::STATISTICS_DIMENSION_MONTH], -2);
			$year = (int) substr($statsReport[PKPStatisticsHelper::STATISTICS_DIMENSION_MONTH], 0, 4);
			$metric = $statsReport[PKPStatisticsHelper::STATISTICS_METRIC];

			// Keep track of the years, avoiding duplicates.
			$years[$year] = null;

			$representationId = $statsReport[PKPStatisticsHelper::STATISTICS_DIMENSION_REPRESENTATION_ID];

			// Prepare the stats aggregating by Representation.
			// Create entries for all months, so all representations will have the same entries count.
			if (!array_key_exists($representationId, $statsByFormat)) {
				$representationDao = Application::getRepresentationDAO();
				$representation = $representationDao->getById($representationId);
				if (empty($representation)) {
					continue;
				}
				$statsByFormat[$representationId] = array(
					'data' => array(),
					'label' => $representation->getLocalizedName(),
					'color' => $this->_getColor($representationId),
					'total' => 0);
			}

			// Make sure we have entries for all years with stats.
			if (!array_key_exists($year, $statsByFormat[$representationId]['data'])) {
				$statsByFormat[$representationId]['data'][$year] = array_fill_keys($months, 0);
			}
			$statsByFormat[$representationId]['data'][$year][$month] = $metric;
			$statsByFormat[$representationId]['total'] += $metric;

			// Prepare the stats aggregating only by Month.
			if (!array_key_exists($year, $statsByMonth)) {
				$statsByMonth[$year] = array_fill_keys($months, 0);
			}
			$statsByMonth[$year][$month] += $metric;
			$totalDownloads += $metric;
		}

		if ($statsByMonth) {
			$datasetId = 'allDownloads'; // GraphJS works with datasets.
			$statsByMonth = array($datasetId => array(
				'data' => $statsByMonth,
				'label' => __('common.allDownloads'),
				'color' => $this->_getColor(REALLY_BIG_NUMBER),
				'total' => $totalDownloads
			));
		}

		return array($statsByFormat, $statsByMonth, array_keys($years));
	}

	/**
	 * Retrieve the `allDownloads` dataset from the download stats
	 *
	 * @param $pubObjectId int ID of the object to get stats for
	 * @param $stats array Optionally pass in stats that have already been
	 *   fetched from _getDownloadStats().
	 * @return $allDownloadStats array The `allDownloads` dataset
	 */
	function getAllDownloadsStats($pubObjectId, $stats = array()) {

		if (empty($stats)) {
			$stats = $this->_getDownloadStats($pubObjectId);
		}

		$allDownloadStats = array();
		foreach($stats as $dataset) {
			if (array_key_exists('allDownloads', $dataset)) {
				$allDownloadStats = $dataset['allDownloads'];
			}
		}

		return $allDownloadStats;
	}

	/**
	 * Callback to fill cache with data, if empty.
	 * @param $cache FileCache
	 * @param $pubObjectId int
	 * @return array
	 */
	function _downloadStatsCacheMiss($cache, $pubObjectId) {
		$filter = array(
				PKPStatisticsHelper::STATISTICS_DIMENSION_SUBMISSION_ID => $pubObjectId,
				PKPStatisticsHelper::STATISTICS_DIMENSION_ASSOC_TYPE => ASSOC_TYPE_SUBMISSION_FILE
		);
		$orderBy = array(PKPStatisticsHelper::STATISTICS_DIMENSION_MONTH => PKPStatisticsHelper::STATISTICS_ORDER_ASC);
		$reportPlugin = $this->getReportPlugin();

		$application = Application::get();

		$statsReports = $application->getMetrics(current($reportPlugin->getMetricTypes()), array(PKPStatisticsHelper::STATISTICS_DIMENSION_MONTH, PKPStatisticsHelper::STATISTICS_DIMENSION_REPRESENTATION_ID), $filter, $orderBy);
		$cache->setEntireCache(array($pubObjectId => $statsReports));
		return $statsReports;
	}

	/**
	 * Return a color RGB code to be used in the graph.
	 * @private
	 * @param $num integer
	 * @return string
	 */
	function _getColor($num) {
		$hash = md5('color' . $num * 2);
		return hexdec(substr($hash, 0, 2)) . ',' . hexdec(substr($hash, 2, 2)) . ',' . hexdec(substr($hash, 4, 2));
	}

	/**
	 * Get context wide setting. If the context or the setting does not exist,
	 * get the site wide setting.
	 * @param $context Context
	 * @param $name Setting name
	 * @return mixed
	 */
	function _getPluginSetting($context, $name) {
		$pluginSettingsDao = DAORegistry::getDAO('PluginSettingsDAO');
		if ($context && $pluginSettingsDao->settingExists($context->getId(), $this->getName(), $name)) {
			return $this->getSetting($context->getId(), $name);
		} else {
			return $this->getSetting(PKPApplication::CONTEXT_ID_NONE, $name);
		}
	}

}