feat: Add Prometheus metrics integration

- Add includes/Prometheus/Integration.php with metrics collection
- Expose content, engagement, user, WooCommerce, and ActivityPub metrics
- Add settings toggle in Integrations tab
- Requires WP Prometheus plugin to be active
- Bump version to 0.5.0

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

CHANGELOG.md

@@ -7,6 +7,38 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.5.0] - 2026-02-02
+
+### Added
+
+- **Prometheus Metrics Integration** - Expose FediStream metrics for monitoring
+  - Content metrics: `fedistream_content_total` (by type/status), `fedistream_genres_total`, `fedistream_moods_total`
+  - Engagement metrics: `fedistream_plays_total`, `fedistream_plays_today`, `fedistream_favorites_total`, `fedistream_local_follows_total`, `fedistream_listening_history_entries`
+  - User metrics: `fedistream_users_with_library`, `fedistream_users_following_artists`, `fedistream_notifications_total`, `fedistream_notifications_pending`
+  - WooCommerce metrics (conditional): `fedistream_purchases_total`, `fedistream_customers_total`, `fedistream_products_total`
+  - ActivityPub metrics (conditional): `fedistream_activitypub_followers_total`, `fedistream_activitypub_followers_by_artist`, `fedistream_activitypub_reactions_total`
+  - New setting in Integrations tab to enable/disable Prometheus metrics
+  - Requires WP Prometheus plugin to be active
+
+## [0.4.9] - 2026-02-02
+
+### Changed
+
+- **Reverted nuclear option** - Restored conditional the_content filter usage
+  - `get_post_data()` now uses the_content filter only when NOT in shortcode context, NOT at depth > 1, and NOT loading page template
+  - All other protections remain in place (render depth, page template loading flag, main template lock, shortcode context)
+  - Memory leak investigation to be continued later
+
+## [0.4.8] - 2026-02-02
+
+### Fixed
+
+- **Nuclear option: NEVER apply the_content filter** - Completely removed the_content filter usage (reverted in 0.4.9)
+  - `get_post_data()` now ALWAYS strips shortcodes and uses raw content
+  - NEVER calls `apply_filters('the_content', ...)` or `get_the_excerpt()`
+  - FediStream posts don't need shortcode processing in their content anyway
+  - This guarantees no recursion through WordPress hook system
+
 ## [0.4.7] - 2026-02-02
 
 ### Fixed
@@ -264,7 +296,9 @@ Initial release of WP FediStream - a WordPress plugin for streaming music over A
 
 ---
 
-[Unreleased]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.7...HEAD
+[Unreleased]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.9...HEAD
+[0.4.9]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.8...v0.4.9
+[0.4.8]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.7...v0.4.8
 [0.4.7]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.6...v0.4.7
 [0.4.6]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.5...v0.4.6
 [0.4.5]: https://src.bundespruefstelle.ch/magdev/wp-fedistream/compare/v0.4.4...v0.4.5

CLAUDE.md

@@ -552,3 +552,58 @@ wp-fedistream/
 - Uses Gitea API directly for release creation (not GitHub Actions)
 - Submodule uses relative URL for CI compatibility
 - Composer symlinks from `lib/wc-licensed-product-client` to vendor
+
+### 2026-02-02 - Memory Leak Investigation v0.4.1 through v0.4.9
+
+**Summary:** Investigated memory exhaustion issue when WP FediStream is used with WP Prometheus plugin. Multiple fix attempts were made but the root cause remains unresolved.
+
+**Problem:**
+
+- PHP Fatal error: Allowed memory size exhausted (1GB)
+- Error locations varied: Twig StagingExtension.php, Environment.php, ExtensionSet.php, WordPress class-wp-hook.php
+- Only occurs when WP Prometheus plugin is also active
+- Suspected infinite recursion through WordPress hook system
+
+**Fix Attempts (v0.4.1 - v0.4.8):**
+
+1. **v0.4.1** - Added recursion depth tracking in `get_post_data()`, skip `the_content` filter at depth > 1
+2. **v0.4.2** - Added `$in_shortcode_context` flag, all shortcode render methods enter context before data loading
+3. **v0.4.3** - Changed boolean to counter (`$shortcode_context_depth`), added context to `template-wrapper.php`
+4. **v0.4.4** - Fixed `get_the_excerpt()` which internally triggers `the_content` filter
+5. **v0.4.5** - Added render depth tracking in `Plugin::render()`, strip shortcodes from content
+6. **v0.4.6** - Added `$loading_page_template` flag to block shortcode rendering during page template loading
+7. **v0.4.7** - Added `$rendering_main_template` hard lock in `Plugin::render()`, reduced MAX_RENDER_DEPTH to 2
+8. **v0.4.8** - Nuclear option: ALWAYS skip `the_content` filter (didn't work, reverted)
+
+**v0.4.9 - Current State:**
+
+- Reverted nuclear option
+- Kept all other protections in place
+- Issue documented in README.md as known incompatibility
+
+**Files Modified:**
+
+- `includes/Frontend/TemplateLoader.php` - Multiple recursion protection mechanisms
+- `includes/Frontend/Shortcodes.php` - Shortcode context entry, page template loading check
+- `includes/Frontend/template-wrapper.php` - Page template loading flag, main template render flag
+- `includes/Plugin.php` - Render depth tracking, main template rendering lock
+- `README.md` - Added Known Issues section
+
+**Protection Mechanisms in Place:**
+
+1. `$recursion_depth` counter in `get_post_data()` (max 3)
+2. `$shortcode_context_depth` counter for nested shortcodes
+3. `$loading_page_template` flag blocks shortcode rendering during page load
+4. `$rendering_main_template` flag in `Plugin::render()` blocks parallel renders
+5. `MAX_RENDER_DEPTH = 2` in `Plugin::render()`
+6. Skip `the_content` and `get_the_excerpt()` when in protected context
+7. Strip shortcodes from content when skipping content filter
+
+**Key Learnings:**
+
+- `get_the_excerpt()` internally calls `apply_filters('the_content', ...)` when generating auto-excerpts
+- `the_content` filter triggers `do_shortcode()` which can cause recursive shortcode processing
+- WordPress hook system (class-wp-hook.php) can itself be the recursion point
+- The interaction between FediStream and WP Prometheus appears to be at a fundamental WordPress level
+
+**Status:** UNRESOLVED - Documented as known incompatibility, investigation to continue later

README.md

@@ -2,7 +2,7 @@
 
 Stream music over ActivityPub - Build your own music streaming platform for Musicians and Labels.
 
-[![Version](https://img.shields.io/badge/version-0.4.0-blue.svg)](CHANGELOG.md)
+[![Version](https://img.shields.io/badge/version-0.5.0-blue.svg)](CHANGELOG.md)
 [![PHP](https://img.shields.io/badge/PHP-%3E%3D8.3-purple.svg)](https://php.net)
 [![WordPress](https://img.shields.io/badge/WordPress-%3E%3D6.4-blue.svg)](https://wordpress.org)
 [![License](https://img.shields.io/badge/license-GPL--2.0%2B-green.svg)](https://www.gnu.org/licenses/gpl-2.0.html)

includes/Frontend/TemplateLoader.php

@@ -292,9 +292,12 @@ class TemplateLoader {
         // Skip the_content filter if:
         // 1. We're in a shortcode context (prevents recursive shortcode processing)
         // 2. We're at depth > 1 (nested data loading)
-        $skip_content_filter = self::$shortcode_context_depth > 0 || self::$recursion_depth > 1;
+        // 3. We're loading a page template
+        $skip_content_filter = self::$shortcode_context_depth > 0
+            || self::$recursion_depth > 1
+            || self::$loading_page_template;
 
-        // When skipping content filter, also use raw excerpt to avoid get_the_excerpt()
+        // When skipping content filter, use raw excerpt to avoid get_the_excerpt()
         // triggering the_content filter internally when generating auto-excerpts.
         if ( $skip_content_filter ) {
             $excerpt = $post->post_excerpt;
@@ -306,7 +309,7 @@ class TemplateLoader {
             $excerpt = get_the_excerpt( $post );
         }
 
-        // When skipping content filter, also strip shortcodes to prevent them from
+        // When skipping content filter, strip shortcodes to prevent them from
         // being processed by anything else that might call do_shortcode on the output.
         if ( $skip_content_filter ) {
             $content = strip_shortcodes( $post->post_content );

includes/Installer.php

@@ -347,6 +347,7 @@ class Installer {
         $defaults = array(
             'wp_fedistream_enable_activitypub'       => 1,
             'wp_fedistream_enable_woocommerce'       => 0,
+            'wp_fedistream_enable_prometheus'        => 0,
             'wp_fedistream_audio_formats'            => array( 'mp3', 'wav', 'flac', 'ogg' ),
             'wp_fedistream_max_upload_size'          => 50, // MB
             'wp_fedistream_default_license'          => 'all-rights-reserved',

includes/Plugin.php

@@ -16,6 +16,7 @@ use WP_FediStream\Frontend\TemplateLoader;
 use WP_FediStream\Frontend\Widgets;
 use WP_FediStream\PostTypes\Artist;
 use WP_FediStream\WooCommerce\Integration as WooCommerceIntegration;
+use WP_FediStream\Prometheus\Integration as PrometheusIntegration;
 use WP_FediStream\WooCommerce\DigitalDelivery;
 use WP_FediStream\WooCommerce\StreamingAccess;
 use WP_FediStream\PostTypes\Album;
@@ -207,6 +208,11 @@ final class Plugin {
             new StreamingAccess();
         }
 
+        // Initialize Prometheus integration.
+        if ( get_option( 'wp_fedistream_enable_prometheus', 0 ) && $this->is_prometheus_active() ) {
+            new PrometheusIntegration();
+        }
+
         // Initialize user library and notifications.
         new UserLibrary();
         new LibraryPage();
@@ -448,6 +454,7 @@ final class Plugin {
         // Get current settings.
         $enable_activitypub = get_option( 'wp_fedistream_enable_activitypub', 1 );
         $enable_woocommerce = get_option( 'wp_fedistream_enable_woocommerce', 0 );
+        $enable_prometheus  = get_option( 'wp_fedistream_enable_prometheus', 0 );
         $max_upload_size    = get_option( 'wp_fedistream_max_upload_size', 50 );
         $default_license    = get_option( 'wp_fedistream_default_license', 'all-rights-reserved' );
 
@@ -486,7 +493,7 @@ final class Plugin {
                         $this->render_settings_tab( $max_upload_size, $default_license );
                         break;
                     case 'integrations':
-                        $this->render_integrations_tab( $enable_activitypub, $enable_woocommerce );
+                        $this->render_integrations_tab( $enable_activitypub, $enable_woocommerce, $enable_prometheus );
                         break;
                 }
                 ?>
@@ -525,6 +532,7 @@ final class Plugin {
             case 'integrations':
                 update_option( 'wp_fedistream_enable_activitypub', isset( $_POST['enable_activitypub'] ) ? 1 : 0 );
                 update_option( 'wp_fedistream_enable_woocommerce', isset( $_POST['enable_woocommerce'] ) ? 1 : 0 );
+                update_option( 'wp_fedistream_enable_prometheus', isset( $_POST['enable_prometheus'] ) ? 1 : 0 );
                 echo '<div class="notice notice-success is-dismissible"><p>' . esc_html__( 'Integration settings saved.', 'wp-fedistream' ) . '</p></div>';
                 break;
         }
@@ -719,9 +727,10 @@ final class Plugin {
      *
      * @param int $enable_activitypub Whether ActivityPub is enabled.
      * @param int $enable_woocommerce Whether WooCommerce integration is enabled.
+     * @param int $enable_prometheus  Whether Prometheus metrics are enabled.
      * @return void
      */
-    private function render_integrations_tab( int $enable_activitypub, int $enable_woocommerce ): void {
+    private function render_integrations_tab( int $enable_activitypub, int $enable_woocommerce, int $enable_prometheus ): void {
         ?>
         <form method="post" action="">
             <?php wp_nonce_field( 'fedistream_save_settings', 'fedistream_settings_nonce' ); ?>
@@ -760,6 +769,23 @@ final class Plugin {
                         <?php endif; ?>
                     </td>
                 </tr>
+                <tr>
+                    <th scope="row"><?php esc_html_e( 'Prometheus Metrics', 'wp-fedistream' ); ?></th>
+                    <td>
+                        <label>
+                            <input type="checkbox" name="enable_prometheus" value="1" <?php checked( $enable_prometheus, 1 ); ?> <?php disabled( ! $this->is_prometheus_active() ); ?>>
+                            <?php esc_html_e( 'Enable Prometheus metrics', 'wp-fedistream' ); ?>
+                        </label>
+                        <?php if ( ! $this->is_prometheus_active() ) : ?>
+                            <p class="description" style="color: #d63638;">
+                                <span class="dashicons dashicons-dismiss" style="font-size: 16px; width: 16px; height: 16px; vertical-align: text-bottom;"></span>
+                                <?php esc_html_e( 'WP Prometheus plugin is not installed or active.', 'wp-fedistream' ); ?>
+                            </p>
+                        <?php else : ?>
+                            <p class="description"><?php esc_html_e( 'Expose FediStream metrics for Prometheus monitoring.', 'wp-fedistream' ); ?></p>
+                        <?php endif; ?>
+                    </td>
+                </tr>
             </table>
 
             <?php submit_button(); ?>
@@ -933,4 +959,13 @@ final class Plugin {
     public function is_activitypub_active(): bool {
         return class_exists( 'Activitypub\Activitypub' );
     }
+
+    /**
+     * Check if WP Prometheus plugin is active.
+     *
+     * @return bool
+     */
+    public function is_prometheus_active(): bool {
+        return defined( 'WP_PROMETHEUS_VERSION' ) || class_exists( 'WP_Prometheus\Plugin' );
+    }
 }

includes/Prometheus/Integration.php

@@ -0,0 +1,422 @@
+<?php
+/**
+ * Prometheus Integration.
+ *
+ * @package WP_FediStream
+ */
+
+namespace WP_FediStream\Prometheus;
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * Main Prometheus integration class.
+ *
+ * Exposes FediStream metrics for Prometheus monitoring via the
+ * wp_prometheus_collect_metrics action hook.
+ */
+class Integration {
+
+	/**
+	 * Whether WP Prometheus is active.
+	 *
+	 * @var bool
+	 */
+	private bool $prometheus_active = false;
+
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		// Check WP Prometheus immediately since we're instantiated during plugins_loaded.
+		$this->check_prometheus();
+
+		// If plugins_loaded hasn't fully completed, hook init at priority 20.
+		// Otherwise, run init directly.
+		if ( ! did_action( 'plugins_loaded' ) || doing_action( 'plugins_loaded' ) ) {
+			add_action( 'plugins_loaded', array( $this, 'init' ), 20 );
+		} else {
+			$this->init();
+		}
+	}
+
+	/**
+	 * Check if WP Prometheus is active.
+	 *
+	 * @return void
+	 */
+	public function check_prometheus(): void {
+		$this->prometheus_active = defined( 'WP_PROMETHEUS_VERSION' )
+			|| class_exists( 'WP_Prometheus\Plugin' );
+	}
+
+	/**
+	 * Initialize Prometheus integration.
+	 *
+	 * @return void
+	 */
+	public function init(): void {
+		if ( ! $this->prometheus_active ) {
+			return;
+		}
+
+		// Register metrics collector.
+		add_action( 'wp_prometheus_collect_metrics', array( $this, 'collect_metrics' ) );
+	}
+
+	/**
+	 * Check if Prometheus is active.
+	 *
+	 * @return bool
+	 */
+	public function is_active(): bool {
+		return $this->prometheus_active;
+	}
+
+	/**
+	 * Collect FediStream metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	public function collect_metrics( $collector ): void {
+		// Register and collect all metric categories.
+		$this->collect_content_metrics( $collector );
+		$this->collect_engagement_metrics( $collector );
+		$this->collect_user_metrics( $collector );
+
+		if ( $this->is_woocommerce_enabled() ) {
+			$this->collect_woocommerce_metrics( $collector );
+		}
+
+		if ( $this->is_activitypub_enabled() ) {
+			$this->collect_activitypub_metrics( $collector );
+		}
+	}
+
+	/**
+	 * Collect content metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	private function collect_content_metrics( $collector ): void {
+		// Content count by type and status.
+		$content_gauge = $collector->register_gauge(
+			'fedistream_content_total',
+			'Total FediStream content count',
+			array( 'type', 'status' )
+		);
+
+		$post_types = array(
+			'fedistream_artist',
+			'fedistream_album',
+			'fedistream_track',
+			'fedistream_playlist',
+		);
+
+		foreach ( $post_types as $post_type ) {
+			$type_label = str_replace( 'fedistream_', '', $post_type );
+			$counts     = wp_count_posts( $post_type );
+
+			foreach ( array( 'publish', 'draft', 'pending' ) as $status ) {
+				$count = isset( $counts->$status ) ? (int) $counts->$status : 0;
+				$content_gauge->set( $count, array( $type_label, $status ) );
+			}
+		}
+
+		// Genre count.
+		$genres_gauge = $collector->register_gauge(
+			'fedistream_genres_total',
+			'Total number of genres',
+			array()
+		);
+		$genre_count  = wp_count_terms( array( 'taxonomy' => 'fedistream_genre' ) );
+		$genres_gauge->set( is_wp_error( $genre_count ) ? 0 : (int) $genre_count, array() );
+
+		// Mood count.
+		$moods_gauge = $collector->register_gauge(
+			'fedistream_moods_total',
+			'Total number of moods',
+			array()
+		);
+		$mood_count  = wp_count_terms( array( 'taxonomy' => 'fedistream_mood' ) );
+		$moods_gauge->set( is_wp_error( $mood_count ) ? 0 : (int) $mood_count, array() );
+	}
+
+	/**
+	 * Collect engagement metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	private function collect_engagement_metrics( $collector ): void {
+		global $wpdb;
+
+		$plays_table     = $wpdb->prefix . 'fedistream_plays';
+		$favorites_table = $wpdb->prefix . 'fedistream_favorites';
+		$follows_table   = $wpdb->prefix . 'fedistream_user_follows';
+		$history_table   = $wpdb->prefix . 'fedistream_listening_history';
+
+		// Total plays.
+		$plays_gauge = $collector->register_gauge(
+			'fedistream_plays_total',
+			'Total track plays',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$total_plays = (int) $wpdb->get_var( "SELECT COUNT(*) FROM {$plays_table}" );
+		$plays_gauge->set( $total_plays, array() );
+
+		// Plays today.
+		$plays_today_gauge = $collector->register_gauge(
+			'fedistream_plays_today',
+			'Track plays today',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$plays_today = (int) $wpdb->get_var(
+			"SELECT COUNT(*) FROM {$plays_table} WHERE DATE(played_at) = CURDATE()"
+		);
+		$plays_today_gauge->set( $plays_today, array() );
+
+		// Favorites by type.
+		$favorites_gauge = $collector->register_gauge(
+			'fedistream_favorites_total',
+			'Total favorites by content type',
+			array( 'type' )
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$favorites_by_type = $wpdb->get_results(
+			"SELECT content_type, COUNT(*) as count FROM {$favorites_table} GROUP BY content_type"
+		);
+		foreach ( $favorites_by_type as $row ) {
+			$favorites_gauge->set( (int) $row->count, array( $row->content_type ) );
+		}
+
+		// Local follows.
+		$follows_gauge = $collector->register_gauge(
+			'fedistream_local_follows_total',
+			'Total local artist follows',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$total_follows = (int) $wpdb->get_var( "SELECT COUNT(*) FROM {$follows_table}" );
+		$follows_gauge->set( $total_follows, array() );
+
+		// Listening history entries.
+		$history_gauge = $collector->register_gauge(
+			'fedistream_listening_history_entries',
+			'Total listening history entries',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$history_count = (int) $wpdb->get_var( "SELECT COUNT(*) FROM {$history_table}" );
+		$history_gauge->set( $history_count, array() );
+	}
+
+	/**
+	 * Collect user metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	private function collect_user_metrics( $collector ): void {
+		global $wpdb;
+
+		$favorites_table     = $wpdb->prefix . 'fedistream_favorites';
+		$follows_table       = $wpdb->prefix . 'fedistream_user_follows';
+		$notifications_table = $wpdb->prefix . 'fedistream_notifications';
+
+		// Users with library (favorites).
+		$users_library_gauge = $collector->register_gauge(
+			'fedistream_users_with_library',
+			'Users who have favorites',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$users_with_library = (int) $wpdb->get_var(
+			"SELECT COUNT(DISTINCT user_id) FROM {$favorites_table}"
+		);
+		$users_library_gauge->set( $users_with_library, array() );
+
+		// Users following artists.
+		$users_following_gauge = $collector->register_gauge(
+			'fedistream_users_following_artists',
+			'Users following at least one artist',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$users_following = (int) $wpdb->get_var(
+			"SELECT COUNT(DISTINCT user_id) FROM {$follows_table}"
+		);
+		$users_following_gauge->set( $users_following, array() );
+
+		// Notifications by type and status.
+		$notifications_gauge = $collector->register_gauge(
+			'fedistream_notifications_total',
+			'Notifications by type and status',
+			array( 'type', 'status' )
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$notifications = $wpdb->get_results(
+			"SELECT type, is_read, COUNT(*) as count FROM {$notifications_table} GROUP BY type, is_read"
+		);
+		foreach ( $notifications as $row ) {
+			$status = $row->is_read ? 'read' : 'unread';
+			$notifications_gauge->set( (int) $row->count, array( $row->type, $status ) );
+		}
+
+		// Pending notifications (simple gauge).
+		$pending_gauge = $collector->register_gauge(
+			'fedistream_notifications_pending',
+			'Total unread notifications',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$pending = (int) $wpdb->get_var(
+			"SELECT COUNT(*) FROM {$notifications_table} WHERE is_read = 0"
+		);
+		$pending_gauge->set( $pending, array() );
+	}
+
+	/**
+	 * Collect WooCommerce metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	private function collect_woocommerce_metrics( $collector ): void {
+		global $wpdb;
+
+		$purchases_table = $wpdb->prefix . 'fedistream_purchases';
+
+		// Purchases by type.
+		$purchases_gauge = $collector->register_gauge(
+			'fedistream_purchases_total',
+			'Total purchases by content type',
+			array( 'type' )
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$purchases = $wpdb->get_results(
+			"SELECT content_type, COUNT(*) as count FROM {$purchases_table} GROUP BY content_type"
+		);
+		foreach ( $purchases as $row ) {
+			$purchases_gauge->set( (int) $row->count, array( $row->content_type ) );
+		}
+
+		// Unique customers.
+		$customers_gauge = $collector->register_gauge(
+			'fedistream_customers_total',
+			'Unique customers with purchases',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$customers = (int) $wpdb->get_var(
+			"SELECT COUNT(DISTINCT user_id) FROM {$purchases_table}"
+		);
+		$customers_gauge->set( $customers, array() );
+
+		// WooCommerce products count (FediStream types).
+		if ( function_exists( 'wc_get_products' ) ) {
+			$products_gauge = $collector->register_gauge(
+				'fedistream_products_total',
+				'FediStream products in WooCommerce',
+				array( 'type' )
+			);
+
+			foreach ( array( 'fedistream_album', 'fedistream_track' ) as $type ) {
+				$products = wc_get_products(
+					array(
+						'type'   => $type,
+						'limit'  => -1,
+						'return' => 'ids',
+					)
+				);
+				$products_gauge->set( count( $products ), array( $type ) );
+			}
+		}
+	}
+
+	/**
+	 * Collect ActivityPub metrics.
+	 *
+	 * @param object $collector The Prometheus collector.
+	 * @return void
+	 */
+	private function collect_activitypub_metrics( $collector ): void {
+		global $wpdb;
+
+		$followers_table = $wpdb->prefix . 'fedistream_followers';
+		$reactions_table = $wpdb->prefix . 'fedistream_reactions';
+
+		// Total ActivityPub followers.
+		$followers_gauge = $collector->register_gauge(
+			'fedistream_activitypub_followers_total',
+			'Total ActivityPub followers across all artists',
+			array()
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$total_followers = (int) $wpdb->get_var( "SELECT COUNT(*) FROM {$followers_table}" );
+		$followers_gauge->set( $total_followers, array() );
+
+		// Followers by artist (top 10 to avoid cardinality explosion).
+		$followers_by_artist_gauge = $collector->register_gauge(
+			'fedistream_activitypub_followers_by_artist',
+			'Followers per artist',
+			array( 'artist_id', 'artist_name' )
+		);
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$followers_by_artist = $wpdb->get_results(
+			"SELECT artist_id, COUNT(*) as count FROM {$followers_table} GROUP BY artist_id ORDER BY count DESC LIMIT 10"
+		);
+		foreach ( $followers_by_artist as $row ) {
+			$artist      = get_post( $row->artist_id );
+			$artist_name = $artist ? $artist->post_title : 'Unknown';
+			$followers_by_artist_gauge->set( (int) $row->count, array( $row->artist_id, $artist_name ) );
+		}
+
+		// Reactions by type (if table exists).
+		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+		$table_exists = $wpdb->get_var(
+			$wpdb->prepare( 'SHOW TABLES LIKE %s', $reactions_table )
+		);
+
+		if ( $table_exists ) {
+			$reactions_gauge = $collector->register_gauge(
+				'fedistream_activitypub_reactions_total',
+				'Fediverse reactions by type',
+				array( 'type' )
+			);
+			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
+			$reactions = $wpdb->get_results(
+				"SELECT reaction_type, COUNT(*) as count FROM {$reactions_table} GROUP BY reaction_type"
+			);
+			foreach ( $reactions as $row ) {
+				$reactions_gauge->set( (int) $row->count, array( $row->reaction_type ) );
+			}
+		}
+	}
+
+	/**
+	 * Check if WooCommerce integration is enabled.
+	 *
+	 * @return bool
+	 */
+	private function is_woocommerce_enabled(): bool {
+		return get_option( 'wp_fedistream_enable_woocommerce', 0 )
+			&& class_exists( 'WooCommerce' );
+	}
+
+	/**
+	 * Check if ActivityPub integration is enabled.
+	 *
+	 * @return bool
+	 */
+	private function is_activitypub_enabled(): bool {
+		return (bool) get_option( 'wp_fedistream_enable_activitypub', 1 );
+	}
+}

includes/Prometheus/index.php

@@ -0,0 +1 @@
+<?php // Silence is golden.

wp-fedistream.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP FediStream
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-fedistream
  * Description: Stream music over ActivityPub - Build your own music streaming platform for Musicians and Labels.
- * Version: 0.4.6
+ * Version: 0.5.0
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -26,7 +26,7 @@ if ( ! defined( 'ABSPATH' ) ) {
  *
  * @var string
  */
-define( 'WP_FEDISTREAM_VERSION', '0.4.7' );
+define( 'WP_FEDISTREAM_VERSION', '0.5.0' );
 
 /**
  * Plugin file path.