Make course lessons publicly previewable by default (#2866)

Closes #2807

wp-content/plugins/wporg-learn/inc/post-meta.php

@@ -22,6 +22,7 @@
 add_action( 'save_post_meeting', __NAMESPACE__ . '\save_meeting_metabox_fields' );
 add_action( 'admin_footer', __NAMESPACE__ . '\render_locales_list' );
 add_action( 'enqueue_block_editor_assets', __NAMESPACE__ . '\enqueue_editor_assets' );
+add_action( 'wp_insert_post', __NAMESPACE__ . '\set_default_lesson_preview', 10, 3 );
 
 /**
  * Register all post meta keys.
@@ -53,6 +54,34 @@ function register_lesson_meta() {
 	);
 }
 
+/**
+ * Set public preview to be enabled on lessons created within a course by default.
+ * This post meta is registered by Sensei with no default value, so we set it here on lesson creation.
+ *
+ * @param int     $post_ID Post ID.
+ * @param WP_Post $post    Post object.
+ * @param bool    $update  Whether this is an existing post being updated.
+ */
+function set_default_lesson_preview( $post_ID, $post, $update ) {
+	// Only run for new lessons.
+	if ( $update || 'lesson' !== $post->post_type ) {
+		return;
+	}
+
+	// Check if the lesson belongs to a course.
+	$course_id = get_post_meta( $post_ID, '_lesson_course', true );
+
+	if ( empty( $course_id ) ) {
+		return;
+	}
+
+	$existing_value = get_post_meta( $post_ID, '_lesson_preview', true );
+
+	if ( '' === $existing_value ) {
+		update_post_meta( $post_ID, '_lesson_preview', 'preview' );
+	}
+}
+
 /**
  * Register post meta keys for lesson plans.
  */