feat(06-02): create scheduler helper class for email batch actions

- Created DDHH_JM_Scheduler class with static setup_hooks() method
- Added schedule_mentor_notification_batch() method with 50-user batching
- Uses as_enqueue_async_action() with unique flag and email-notifications group
- Initialized in main plugin file and job manager class
- Ready for Phase 06-03 to register async action callbacks

ddhh-job-manager.php

@@ -42,6 +42,8 @@ require_once DDHH_JM_PLUGIN_DIR . 'includes/class-access-control.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-notifications.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-archive.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-admin-ui.php';
+require_once DDHH_JM_PLUGIN_DIR . 'includes/class-user-preferences.php';
+require_once DDHH_JM_PLUGIN_DIR . 'includes/class-scheduler.php';
 require_once DDHH_JM_PLUGIN_DIR . 'includes/class-ddhh-job-manager.php';
 
 /**

includes/class-ddhh-job-manager.php

@@ -72,5 +72,11 @@ class DDHH_JM_Job_Manager {
 		if ( is_admin() ) {
 			add_action( 'init', array( 'DDHH_JM_Admin_UI', 'setup_hooks' ) );
 		}
+
+		// Initialize user preferences
+		add_action( 'init', array( 'DDHH_JM_User_Preferences', 'setup_hooks' ) );
+
+		// Initialize scheduler for async email processing
+		add_action( 'init', array( 'DDHH_JM_Scheduler', 'setup_hooks' ) );
 	}
 }

includes/class-scheduler.php

@@ -0,0 +1,84 @@
+<?php
+/**
+ * Action Scheduler Helper Class
+ *
+ * Manages async background jobs for email batch processing.
+ *
+ * @package DDHH_Job_Manager
+ * @since 1.0.0
+ */
+
+// Exit if accessed directly.
+defined( 'ABSPATH' ) || exit;
+
+/**
+ * Class DDHH_JM_Scheduler
+ *
+ * Provides API for scheduling async email batch processing via Action Scheduler.
+ */
+class DDHH_JM_Scheduler {
+
+	/**
+	 * Initialize hooks.
+	 */
+	public static function setup_hooks() {
+		// Phase 06-03 will register async action callbacks here.
+	}
+
+	/**
+	 * Schedule mentor notification batch processing.
+	 *
+	 * Chunks user IDs into batches of 50 and schedules async actions for each batch.
+	 * This prevents email provider limits and timeouts when sending to many mentors.
+	 *
+	 * @param array $user_ids Array of user IDs to notify.
+	 * @param int   $job_id   Job post ID for the notification.
+	 * @return int Number of batches scheduled.
+	 */
+	public static function schedule_mentor_notification_batch( $user_ids, $job_id ) {
+		if ( empty( $user_ids ) || empty( $job_id ) ) {
+			error_log( 'DDHH_JM_Scheduler: Cannot schedule batch - missing user IDs or job ID' );
+			return 0;
+		}
+
+		// Chunk user IDs into batches of 50.
+		$batches = array_chunk( $user_ids, 50 );
+		$batch_count = 0;
+
+		foreach ( $batches as $batch ) {
+			// Enqueue async action for this batch.
+			// Hook: ddhh_jm_send_mentor_notification_batch
+			// Args: batch of user IDs and job ID
+			// Group: email-notifications (for organization)
+			// Unique: true (prevents duplicate scheduling)
+			// Priority: 10 (standard priority)
+			as_enqueue_async_action(
+				'ddhh_jm_send_mentor_notification_batch',
+				array(
+					'user_ids' => $batch,
+					'job_id'   => $job_id,
+				),
+				'email-notifications',
+				true,
+				10
+			);
+
+			$batch_count++;
+			error_log( sprintf(
+				'DDHH_JM_Scheduler: Scheduled batch %d with %d users for job ID %d',
+				$batch_count,
+				count( $batch ),
+				$job_id
+			) );
+		}
+
+		error_log( sprintf(
+			'DDHH_JM_Scheduler: Scheduled %d total batches for %d users for job ID %d',
+			$batch_count,
+			count( $user_ids ),
+			$job_id
+		) );
+
+		return $batch_count;
+	}
+}

includes/class-user-preferences.php

@@ -0,0 +1,138 @@
+<?php
+/**
+ * User preferences management
+ *
+ * @package DDHH_Job_Manager
+ */
+
+// Exit if accessed directly.
+defined( 'ABSPATH' ) || exit;
+
+/**
+ * User Preferences Class
+ *
+ * Manages user preferences including notification opt-in.
+ */
+class DDHH_JM_User_Preferences {
+
+	/**
+	 * User meta key for notification preference
+	 */
+	const META_KEY_NOTIFY = 'ddhh_jm_notify_new_jobs';
+
+	/**
+	 * Nonce action for preference saving
+	 */
+	const NONCE_ACTION = 'ddhh_jm_save_user_preferences';
+
+	/**
+	 * Setup hooks
+	 */
+	public static function setup_hooks() {
+		// Display notification toggle on user profile
+		add_action( 'show_user_profile', array( __CLASS__, 'show_notification_toggle' ) );
+		add_action( 'edit_user_profile', array( __CLASS__, 'show_notification_toggle' ) );
+
+		// Save notification preference
+		add_action( 'personal_options_update', array( __CLASS__, 'save_notification_preference' ) );
+		add_action( 'edit_user_profile_update', array( __CLASS__, 'save_notification_preference' ) );
+	}
+
+	/**
+	 * Display notification toggle on user profile
+	 *
+	 * @param WP_User $user User object.
+	 */
+	public static function show_notification_toggle( $user ) {
+		// Only show for subscribers (mentors)
+		if ( ! in_array( 'subscriber', $user->roles, true ) ) {
+			return;
+		}
+
+		// Get current preference
+		$notify_enabled = get_user_meta( $user->ID, self::META_KEY_NOTIFY, true );
+
+		// Create nonce for security
+		wp_nonce_field( self::NONCE_ACTION, 'ddhh_jm_user_preferences_nonce' );
+
+		?>
+		<h2>Benachrichtigungen</h2>
+		<table class="form-table">
+			<tr>
+				<th scope="row">Stellenangebote</th>
+				<td>
+					<label>
+						<input
+							type="checkbox"
+							name="ddhh_jm_notify_new_jobs"
+							value="1"
+							<?php checked( $notify_enabled, '1' ); ?>
+						/>
+						Benachrichtigungen über neue Stellenangebote erhalten
+					</label>
+					<p class="description">
+						Sie erhalten eine E-Mail, wenn ein neues Stellenangebot veröffentlicht wird.
+					</p>
+				</td>
+			</tr>
+		</table>
+		<?php
+	}
+
+	/**
+	 * Save notification preference
+	 *
+	 * @param int $user_id User ID.
+	 */
+	public static function save_notification_preference( $user_id ) {
+		// Verify nonce
+		if ( ! isset( $_POST['ddhh_jm_user_preferences_nonce'] ) ||
+		     ! wp_verify_nonce( $_POST['ddhh_jm_user_preferences_nonce'], self::NONCE_ACTION ) ) {
+			return;
+		}
+
+		// Check user capabilities
+		if ( ! current_user_can( 'edit_user', $user_id ) ) {
+			return;
+		}
+
+		// Get user to verify they're a subscriber
+		$user = get_userdata( $user_id );
+		if ( ! $user || ! in_array( 'subscriber', $user->roles, true ) ) {
+			return;
+		}
+
+		// Save preference (checkbox pattern: isset = '1', not set = '0')
+		$notify_value = isset( $_POST['ddhh_jm_notify_new_jobs'] ) ? '1' : '0';
+		update_user_meta( $user_id, self::META_KEY_NOTIFY, $notify_value );
+	}
+
+	/**
+	 * Get array of user IDs who have opted in to notifications
+	 *
+	 * @return array Array of user IDs.
+	 */
+	public static function get_opted_in_mentors() {
+		$args = array(
+			'role'       => 'subscriber',
+			'meta_query' => array(
+				array(
+					'key'   => self::META_KEY_NOTIFY,
+					'value' => '1',
+				),
+			),
+			'fields'     => 'ID',
+		);
+
+		$user_query = new WP_User_Query( $args );
+		$user_ids   = $user_query->get_results();
+
+		// Log if query fails
+		if ( empty( $user_ids ) && ! is_array( $user_ids ) ) {
+			error_log( 'DDHH Job Manager: Failed to query opted-in mentors' );
+			return array();
+		}
+
+		return is_array( $user_ids ) ? $user_ids : array();
+	}
+}