Add Prometheus metrics integration (v0.7.4)

- New Metrics settings tab with enable/disable toggle
- PrometheusController for wp_prometheus_collect_metrics hook
- License gauges: total by status, lifetime, expiring, expiring soon
- Download gauges: total downloads, active versions
- API counters: requests, rate limits, validation errors
- Metric tracking in RestApiController and UpdateController

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,28 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.7.4] - 2026-02-03
+
+### Added
+
+- **Prometheus Metrics Integration**: Expose license and API metrics for monitoring
+  - New "Metrics" settings tab with enable/disable toggle
+  - License gauges: total by status, lifetime, expiring, expiring soon
+  - Download gauges: total downloads, active versions count
+  - API counters: requests by endpoint/result, rate limit exceeded events, validation errors by type
+  - Requires [WP Prometheus](https://src.bundespruefstelle.ch/magdev/wp-prometheus) plugin
+
+### New Files
+
+- `src/Metrics/PrometheusController.php` - Prometheus metrics collection and registration
+
+### Technical Details
+
+- Hooks into `wp_prometheus_collect_metrics` action for metric collection
+- API counters stored persistently in WordPress options (`wclp_prometheus_counters`)
+- Static methods for incrementing counters from API controllers
+- Metrics only collected when enabled in settings
+
 ## [0.7.3] - 2026-02-01
 
 ### Fixed

src/Admin/SettingsController.php

@@ -65,6 +65,7 @@ final class SettingsController
             'auto-updates' => __('Auto-Updates', 'wc-licensed-product'),
             'defaults' => __('Default Settings', 'wc-licensed-product'),
             'notifications' => __('Notifications', 'wc-licensed-product'),
+            'metrics' => __('Metrics', 'wc-licensed-product'),
         ];
     }
 
@@ -116,6 +117,7 @@ final class SettingsController
             'auto-updates' => $this->getAutoUpdatesSettings(),
             'defaults' => $this->getDefaultsSettings(),
             'notifications' => $this->getNotificationsSettings(),
+            'metrics' => $this->getMetricsSettings(),
             default => $this->getPluginLicenseSettings(),
         };
     }
@@ -314,6 +316,32 @@ final class SettingsController
         ];
     }
 
+    /**
+     * Get metrics settings
+     */
+    private function getMetricsSettings(): array
+    {
+        return [
+            'metrics_section_title' => [
+                'name' => __('Prometheus Metrics', 'wc-licensed-product'),
+                'type' => 'title',
+                'desc' => __('Expose license and API metrics for Prometheus monitoring. Requires the WP Prometheus plugin to be installed and active.', 'wc-licensed-product'),
+                'id' => 'wc_licensed_product_section_metrics',
+            ],
+            'metrics_enabled' => [
+                'name' => __('Enable Prometheus Metrics', 'wc-licensed-product'),
+                'type' => 'checkbox',
+                'desc' => __('Expose license statistics, API usage, and download metrics via Prometheus.', 'wc-licensed-product'),
+                'id' => 'wc_licensed_product_metrics_enabled',
+                'default' => 'no',
+            ],
+            'metrics_section_end' => [
+                'type' => 'sectionend',
+                'id' => 'wc_licensed_product_section_metrics_end',
+            ],
+        ];
+    }
+
     /**
      * Render settings tab content
      */
@@ -575,4 +603,12 @@ final class SettingsController
             wp_send_json_error(['message' => $error]);
         }
     }
+
+    /**
+     * Check if Prometheus metrics are enabled
+     */
+    public static function isMetricsEnabled(): bool
+    {
+        return get_option('wc_licensed_product_metrics_enabled', 'no') === 'yes';
+    }
 }

src/Api/RestApiController.php

@@ -10,6 +10,7 @@ declare(strict_types=1);
 namespace Jeremias\WcLicensedProduct\Api;
 
 use Jeremias\WcLicensedProduct\License\LicenseManager;
+use Jeremias\WcLicensedProduct\Metrics\PrometheusController;
 use WP_REST_Request;
 use WP_REST_Response;
 use WP_REST_Server;
@@ -108,6 +109,10 @@ final class RestApiController
                 'retry_after' => $retryAfter,
             ], 429);
             $response->header('Retry-After', (string) $retryAfter);
+
+            // Track rate limit event for metrics
+            PrometheusController::incrementRateLimitExceeded('api');
+
             return $response;
         }
 
@@ -209,6 +214,16 @@ final class RestApiController
 
         $statusCode = $this->getStatusCodeForResult($result);
 
+        // Track metrics
+        if ($result['valid']) {
+            PrometheusController::incrementApiRequest('validate', 'success');
+        } else {
+            PrometheusController::incrementApiRequest('validate', 'error');
+            if (!empty($result['error'])) {
+                PrometheusController::incrementValidationError($result['error']);
+            }
+        }
+
         return new WP_REST_Response($result, $statusCode);
     }
 
@@ -247,6 +262,9 @@ final class RestApiController
         $license = $this->licenseManager->getLicenseByKey($licenseKey);
 
         if (!$license) {
+            PrometheusController::incrementApiRequest('status', 'error');
+            PrometheusController::incrementValidationError('license_not_found');
+
             return new WP_REST_Response([
                 'valid' => false,
                 'error' => 'license_not_found',
@@ -254,6 +272,8 @@ final class RestApiController
             ], 404);
         }
 
+        PrometheusController::incrementApiRequest('status', 'success');
+
         return new WP_REST_Response([
             'valid' => $license->isValid(),
             'status' => $license->getStatus(),
@@ -280,6 +300,9 @@ final class RestApiController
         $license = $this->licenseManager->getLicenseByKey($licenseKey);
 
         if (!$license) {
+            PrometheusController::incrementApiRequest('activate', 'error');
+            PrometheusController::incrementValidationError('license_not_found');
+
             return new WP_REST_Response([
                 'success' => false,
                 'error' => 'license_not_found',
@@ -288,6 +311,9 @@ final class RestApiController
         }
 
         if (!$license->isValid()) {
+            PrometheusController::incrementApiRequest('activate', 'error');
+            PrometheusController::incrementValidationError('license_invalid');
+
             return new WP_REST_Response([
                 'success' => false,
                 'error' => 'license_invalid',
@@ -299,6 +325,8 @@ final class RestApiController
 
         // Check if already activated on this domain
         if ($license->getDomain() === $normalizedDomain) {
+            PrometheusController::incrementApiRequest('activate', 'success');
+
             return new WP_REST_Response([
                 'success' => true,
                 'message' => __('License is already activated for this domain.', 'wc-licensed-product'),
@@ -307,6 +335,9 @@ final class RestApiController
 
         // Check if can activate on another domain
         if (!$license->canActivate()) {
+            PrometheusController::incrementApiRequest('activate', 'error');
+            PrometheusController::incrementValidationError('max_activations_reached');
+
             return new WP_REST_Response([
                 'success' => false,
                 'error' => 'max_activations_reached',
@@ -318,6 +349,9 @@ final class RestApiController
         $success = $this->licenseManager->updateLicenseDomain($license->getId(), $domain);
 
         if (!$success) {
+            PrometheusController::incrementApiRequest('activate', 'error');
+            PrometheusController::incrementValidationError('activation_failed');
+
             return new WP_REST_Response([
                 'success' => false,
                 'error' => 'activation_failed',
@@ -325,6 +359,8 @@ final class RestApiController
             ], 500);
         }
 
+        PrometheusController::incrementApiRequest('activate', 'success');
+
         return new WP_REST_Response([
             'success' => true,
             'message' => __('License activated successfully.', 'wc-licensed-product'),

src/Api/UpdateController.php

@@ -12,6 +12,7 @@ declare(strict_types=1);
 namespace Jeremias\WcLicensedProduct\Api;
 
 use Jeremias\WcLicensedProduct\License\LicenseManager;
+use Jeremias\WcLicensedProduct\Metrics\PrometheusController;
 use Jeremias\WcLicensedProduct\Product\VersionManager;
 use Jeremias\WcLicensedProduct\Product\ProductVersion;
 use WP_REST_Request;
@@ -113,6 +114,10 @@ final class UpdateController
                 'retry_after' => $retryAfter,
             ], 429);
             $response->header('Retry-After', (string) $retryAfter);
+
+            // Track rate limit event for metrics
+            PrometheusController::incrementRateLimitExceeded('update-check');
+
             return $response;
         }
 
@@ -179,10 +184,14 @@ final class UpdateController
         $validationResult = $this->licenseManager->validateLicense($licenseKey, $domain);
 
         if (!$validationResult['valid']) {
+            $errorType = $validationResult['error'] ?? 'license_invalid';
+            PrometheusController::incrementApiRequest('update-check', 'error');
+            PrometheusController::incrementValidationError($errorType);
+
             return new WP_REST_Response([
                 'success' => false,
                 'update_available' => false,
-                'error' => $validationResult['error'] ?? 'license_invalid',
+                'error' => $errorType,
                 'message' => $validationResult['message'] ?? __('License validation failed.', 'wc-licensed-product'),
             ], $validationResult['error'] === 'license_not_found' ? 404 : 403);
         }
@@ -190,6 +199,9 @@ final class UpdateController
         // Get license to access product ID
         $license = $this->licenseManager->getLicenseByKey($licenseKey);
         if (!$license) {
+            PrometheusController::incrementApiRequest('update-check', 'error');
+            PrometheusController::incrementValidationError('license_not_found');
+
             return new WP_REST_Response([
                 'success' => false,
                 'update_available' => false,
@@ -202,6 +214,9 @@ final class UpdateController
         $product = wc_get_product($productId);
 
         if (!$product) {
+            PrometheusController::incrementApiRequest('update-check', 'error');
+            PrometheusController::incrementValidationError('product_not_found');
+
             return new WP_REST_Response([
                 'success' => false,
                 'update_available' => false,
@@ -214,6 +229,8 @@ final class UpdateController
         $latestVersion = $this->getLatestVersionForLicense($license);
 
         if (!$latestVersion) {
+            PrometheusController::incrementApiRequest('update-check', 'success');
+
             return new WP_REST_Response([
                 'success' => true,
                 'update_available' => false,
@@ -230,6 +247,8 @@ final class UpdateController
         // Build response
         $response = $this->buildUpdateResponse($product, $latestVersion, $license, $updateAvailable);
 
+        PrometheusController::incrementApiRequest('update-check', 'success');
+
         return new WP_REST_Response($response);
     }
 

src/Metrics/PrometheusController.php

@@ -0,0 +1,259 @@
+<?php
+/**
+ * Prometheus Metrics Controller
+ *
+ * @package Jeremias\WcLicensedProduct\Metrics
+ */
+
+declare(strict_types=1);
+
+namespace Jeremias\WcLicensedProduct\Metrics;
+
+use Jeremias\WcLicensedProduct\Admin\SettingsController;
+use Jeremias\WcLicensedProduct\License\LicenseManager;
+use Jeremias\WcLicensedProduct\Product\VersionManager;
+
+/**
+ * Exposes license and API metrics for Prometheus monitoring
+ */
+final class PrometheusController
+{
+    /**
+     * Option name for storing API counters
+     */
+    private const COUNTERS_OPTION = 'wclp_prometheus_counters';
+
+    private LicenseManager $licenseManager;
+    private VersionManager $versionManager;
+
+    public function __construct(LicenseManager $licenseManager, VersionManager $versionManager)
+    {
+        $this->licenseManager = $licenseManager;
+        $this->versionManager = $versionManager;
+    }
+
+    /**
+     * Register hooks for Prometheus metrics collection
+     */
+    public function register(): void
+    {
+        // Only register if metrics are enabled
+        if (!SettingsController::isMetricsEnabled()) {
+            return;
+        }
+
+        add_action('wp_prometheus_collect_metrics', [$this, 'collectMetrics']);
+    }
+
+    /**
+     * Collect and register all metrics
+     *
+     * @param object $collector The Prometheus collector object
+     */
+    public function collectMetrics(object $collector): void
+    {
+        $this->collectLicenseMetrics($collector);
+        $this->collectDownloadMetrics($collector);
+        $this->collectApiMetrics($collector);
+    }
+
+    /**
+     * Collect license-related metrics
+     */
+    private function collectLicenseMetrics(object $collector): void
+    {
+        $stats = $this->licenseManager->getStatistics();
+
+        // License count by status (gauge)
+        $licensesByStatus = $collector->register_gauge(
+            'wclp_licenses_total',
+            'Total number of licenses by status',
+            ['status']
+        );
+
+        foreach ($stats['by_status'] as $status => $count) {
+            $licensesByStatus->set($count, [$status]);
+        }
+
+        // Lifetime licenses (gauge)
+        $lifetimeLicenses = $collector->register_gauge(
+            'wclp_licenses_lifetime_total',
+            'Total number of lifetime licenses'
+        );
+        $lifetimeLicenses->set($stats['lifetime']);
+
+        // Expiring licenses (gauge)
+        $expiringLicenses = $collector->register_gauge(
+            'wclp_licenses_expiring_total',
+            'Total number of licenses with expiration date'
+        );
+        $expiringLicenses->set($stats['expiring']);
+
+        // Licenses expiring soon - next 30 days (gauge)
+        $expiringSoon = $collector->register_gauge(
+            'wclp_licenses_expiring_soon',
+            'Licenses expiring within 30 days'
+        );
+        $expiringSoon->set($stats['expiring_soon']);
+    }
+
+    /**
+     * Collect download-related metrics
+     */
+    private function collectDownloadMetrics(object $collector): void
+    {
+        $stats = $this->versionManager->getDownloadStatistics();
+
+        // Total downloads (gauge)
+        $totalDownloads = $collector->register_gauge(
+            'wclp_downloads_total',
+            'Total number of file downloads'
+        );
+        $totalDownloads->set($stats['total']);
+
+        // Active versions count (gauge)
+        $activeVersions = $collector->register_gauge(
+            'wclp_versions_active_total',
+            'Total number of active product versions'
+        );
+        $activeVersions->set($this->countActiveVersions());
+    }
+
+    /**
+     * Collect API-related metrics (counters)
+     */
+    private function collectApiMetrics(object $collector): void
+    {
+        $counters = $this->getCounters();
+
+        // API requests by endpoint and result (counter)
+        $apiRequests = $collector->register_counter(
+            'wclp_api_requests_total',
+            'Total API requests by endpoint and result',
+            ['endpoint', 'result']
+        );
+
+        foreach ($counters['api_requests'] ?? [] as $key => $count) {
+            [$endpoint, $result] = explode(':', $key);
+            $apiRequests->incBy($count, [$endpoint, $result]);
+        }
+
+        // Rate limit exceeded events (counter)
+        $rateLimitExceeded = $collector->register_counter(
+            'wclp_rate_limit_exceeded_total',
+            'Total rate limit exceeded events by endpoint',
+            ['endpoint']
+        );
+
+        foreach ($counters['rate_limit'] ?? [] as $endpoint => $count) {
+            $rateLimitExceeded->incBy($count, [$endpoint]);
+        }
+
+        // Validation errors by type (counter)
+        $validationErrors = $collector->register_counter(
+            'wclp_validation_errors_total',
+            'Total validation errors by error type',
+            ['error_type']
+        );
+
+        foreach ($counters['validation_errors'] ?? [] as $errorType => $count) {
+            $validationErrors->incBy($count, [$errorType]);
+        }
+    }
+
+    /**
+     * Count active product versions
+     */
+    private function countActiveVersions(): int
+    {
+        global $wpdb;
+
+        $tableName = \Jeremias\WcLicensedProduct\Installer::getVersionsTable();
+
+        return (int) $wpdb->get_var(
+            "SELECT COUNT(*) FROM {$tableName} WHERE is_active = 1"
+        );
+    }
+
+    /**
+     * Get stored counters
+     */
+    private function getCounters(): array
+    {
+        $counters = get_option(self::COUNTERS_OPTION, []);
+        return is_array($counters) ? $counters : [];
+    }
+
+    /**
+     * Increment an API request counter
+     *
+     * @param string $endpoint The API endpoint (validate, status, activate, update-check)
+     * @param string $result The result (success or error)
+     */
+    public static function incrementApiRequest(string $endpoint, string $result): void
+    {
+        if (!SettingsController::isMetricsEnabled()) {
+            return;
+        }
+
+        $counters = get_option(self::COUNTERS_OPTION, []);
+        if (!is_array($counters)) {
+            $counters = [];
+        }
+
+        $key = "{$endpoint}:{$result}";
+        $counters['api_requests'][$key] = ($counters['api_requests'][$key] ?? 0) + 1;
+
+        update_option(self::COUNTERS_OPTION, $counters, false);
+    }
+
+    /**
+     * Increment rate limit exceeded counter
+     *
+     * @param string $endpoint The API endpoint
+     */
+    public static function incrementRateLimitExceeded(string $endpoint): void
+    {
+        if (!SettingsController::isMetricsEnabled()) {
+            return;
+        }
+
+        $counters = get_option(self::COUNTERS_OPTION, []);
+        if (!is_array($counters)) {
+            $counters = [];
+        }
+
+        $counters['rate_limit'][$endpoint] = ($counters['rate_limit'][$endpoint] ?? 0) + 1;
+
+        update_option(self::COUNTERS_OPTION, $counters, false);
+    }
+
+    /**
+     * Increment validation error counter
+     *
+     * @param string $errorType The error type (license_not_found, domain_mismatch, etc.)
+     */
+    public static function incrementValidationError(string $errorType): void
+    {
+        if (!SettingsController::isMetricsEnabled()) {
+            return;
+        }
+
+        $counters = get_option(self::COUNTERS_OPTION, []);
+        if (!is_array($counters)) {
+            $counters = [];
+        }
+
+        $counters['validation_errors'][$errorType] = ($counters['validation_errors'][$errorType] ?? 0) + 1;
+
+        update_option(self::COUNTERS_OPTION, $counters, false);
+    }
+
+    /**
+     * Reset all counters (useful for testing or maintenance)
+     */
+    public static function resetCounters(): void
+    {
+        delete_option(self::COUNTERS_OPTION);
+    }
+}

src/Plugin.php

@@ -26,6 +26,7 @@ use Jeremias\WcLicensedProduct\Frontend\AccountController;
 use Jeremias\WcLicensedProduct\Frontend\DownloadController;
 use Jeremias\WcLicensedProduct\License\LicenseManager;
 use Jeremias\WcLicensedProduct\License\PluginLicenseChecker;
+use Jeremias\WcLicensedProduct\Metrics\PrometheusController;
 use Jeremias\WcLicensedProduct\Product\LicensedProductType;
 use Jeremias\WcLicensedProduct\Product\VersionManager;
 use Jeremias\WcLicensedProduct\Update\PluginUpdateChecker;
@@ -171,6 +172,9 @@ final class Plugin
         if (!empty($serverUrl) && !$licenseChecker->isSelfLicensing()) {
             PluginUpdateChecker::getInstance()->register();
         }
+
+        // Initialize Prometheus metrics if enabled
+        (new PrometheusController($this->licenseManager, $this->versionManager))->register();
     }
 
     /**

wc-licensed-product.php

@@ -3,7 +3,7 @@
  * Plugin Name: WooCommerce Licensed Product
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wc-licensed-product
  * Description: WooCommerce plugin to sell software products using license keys with domain-based validation.
- * Version: 0.7.3
+ * Version: 0.7.4
  * Author: Marco Graetsch
  * Author URI: https://src.bundespruefstelle.ch/magdev
  * License: GPL-2.0-or-later
@@ -28,7 +28,7 @@ if (!defined('ABSPATH')) {
 }
 
 // Plugin constants
-define('WC_LICENSED_PRODUCT_VERSION', '0.7.3');
+define('WC_LICENSED_PRODUCT_VERSION', '0.7.4');
 define('WC_LICENSED_PRODUCT_PLUGIN_FILE', __FILE__);
 define('WC_LICENSED_PRODUCT_PLUGIN_DIR', plugin_dir_path(__FILE__));
 define('WC_LICENSED_PRODUCT_PLUGIN_URL', plugin_dir_url(__FILE__));