feat(admin): screen options on the picker page

Wires WordPress's standard Screen Options dropdown for the picker:

- Per-page setting backed by user meta (msls_tp_per_page) with a 20-item
  default, persisted via the set-screen-option / set_screen_option_*
  filters. The list table reads it through get_items_per_page so the
  pagination args reflect the user's choice.

- Column toggles surface automatically: on load-<hook> we register a
  manage_<screen>_columns filter that returns the table's columns. WP
  then renders a checkbox per column and stores hidden ones in
  manage<screen>columnshidden user meta. prepare_items now passes
  get_hidden_columns into _column_headers so hidden columns are
  honored at render time.

The columns filter instantiates a temporary table without requiring a
source blog, so the toggle list is available before the user picks a
source. Taxonomy lookup falls back to the current (target) blog when
no source is set.

Author: apermo

includes/MslsTranslationPickerPage.php

@@ -22,6 +22,10 @@ class MslsTranslationPickerPage {
 
 	const SCRIPT_HANDLE = 'msls-translation-picker';
 
+	const PER_PAGE_OPTION = 'msls_tp_per_page';
+
+	const PER_PAGE_DEFAULT = 20;
+
 	/**
 	 * Kept for template callers that reference a single slug; equal to
 	 * the base slug for the 'post' post type.
@@ -36,6 +40,26 @@ public static function init(): void {
 		// Late-priority reorder: put our entries right under "All Posts"
 		// regardless of what other plugins do to the submenu array.
 		add_action( 'admin_menu', array( self::class, 'reorder_submenu' ), 999 );
+
+		add_filter( 'set-screen-option', array( self::class, 'save_per_page_option' ), 10, 3 );
+		add_filter( 'set_screen_option_' . self::PER_PAGE_OPTION, array( self::class, 'save_per_page_option' ), 10, 3 );
+	}
+
+	/**
+	 * Persists the chosen per-page value submitted via screen options.
+	 *
+	 * @param mixed  $status
+	 * @param string $option
+	 * @param mixed  $value
+	 *
+	 * @return mixed
+	 */
+	public static function save_per_page_option( $status, $option, $value ) {
+		if ( self::PER_PAGE_OPTION === $option ) {
+			$value = (int) $value;
+			return $value > 0 ? $value : self::PER_PAGE_DEFAULT;
+		}
+		return $status;
 	}
 
 	/**
@@ -53,17 +77,62 @@ public static function register(): void {
 				continue;
 			}
 
-			add_submenu_page(
+			$hook = add_submenu_page(
 				$parent,
 				__( 'Add Post from Translation', 'multisite-language-switcher' ),
 				__( 'Add from Translation', 'multisite-language-switcher' ),
 				'edit_posts',
 				self::page_slug( $post_type ),
 				array( self::class, 'render' )
 			);
+
+			if ( $hook ) {
+				add_action(
+					'load-' . $hook,
+					static function () use ( $post_type ) {
+						MslsTranslationPickerPage::on_page_load( $post_type );
+					}
+				);
+			}
 		}
 	}
 
+	/**
+	 * Called once per request when the picker page is being loaded for a
+	 * specific post type. Registers the screen options (per-page and the
+	 * automatic column-toggle dropdown).
+	 *
+	 * @codeCoverageIgnore
+	 */
+	public static function on_page_load( string $post_type ): void {
+		add_screen_option(
+			'per_page',
+			array(
+				'label'   => __( 'Posts per page', 'multisite-language-switcher' ),
+				'default' => self::PER_PAGE_DEFAULT,
+				'option'  => self::PER_PAGE_OPTION,
+			)
+		);
+
+		$screen = get_current_screen();
+		if ( ! $screen ) {
+			return;
+		}
+
+		// Surface the table's columns to WordPress so the screen-options
+		// dropdown shows toggles for them and hidden-column user prefs
+		// persist through manage{$screen->id}columnshidden.
+		add_filter(
+			'manage_' . $screen->id . '_columns',
+			static function () use ( $post_type ) {
+				// phpcs:ignore WordPress.Security.NonceVerification.Recommended
+				$source = isset( $_GET['msls_source'] ) ? absint( wp_unslash( (string) $_GET['msls_source'] ) ) : 0;
+				$table  = new MslsTranslationPickerTable( $source, $post_type );
+				return $table->get_columns();
+			}
+		);
+	}
+
 	/**
 	 * Moves each of our submenu entries to the slot directly after the
 	 * parent's first item ("All Posts" / "All Pages" / "All CPTs"). Runs

includes/MslsTranslationPickerTable.php

@@ -80,14 +80,22 @@ protected function get_admin_column_taxonomies(): array {
 			return $this->taxonomies_cache;
 		}
 
-		switch_to_blog( $this->source_blog_id );
+		$switched = false;
+		if ( $this->source_blog_id > 0 ) {
+			switch_to_blog( $this->source_blog_id );
+			$switched = true;
+		}
+
 		$this->taxonomies_cache = array();
 		foreach ( get_object_taxonomies( $this->post_type, 'objects' ) as $tax ) {
 			if ( ! empty( $tax->show_admin_column ) ) {
 				$this->taxonomies_cache[ $tax->name ] = $tax;
 			}
 		}
-		restore_current_blog();
+
+		if ( $switched ) {
+			restore_current_blog();
+		}
 
 		return $this->taxonomies_cache;
 	}
@@ -99,10 +107,13 @@ protected function get_bulk_actions(): array {
 	}
 
 	public function prepare_items(): void {
-		$this->_column_headers = array( $this->get_columns(), array(), array() );
+		$columns               = $this->get_columns();
+		$hidden                = is_object( $this->screen ) ? get_hidden_columns( $this->screen ) : array();
+		$this->_column_headers = array( $columns, $hidden, array() );
 
 		$target_lang  = MslsBlogCollection::get_blog_language( get_current_blog_id() );
 		$current_page = $this->get_pagenum();
+		$per_page     = (int) $this->get_items_per_page( MslsTranslationPickerPage::PER_PAGE_OPTION, self::PER_PAGE );
 
 		switch_to_blog( $this->source_blog_id );
 
@@ -111,7 +122,7 @@ public function prepare_items(): void {
 		$args = array(
 			'post_type'      => $this->post_type,
 			'post_status'    => array( 'publish', 'draft', 'pending', 'future' ),
-			'posts_per_page' => self::PER_PAGE,
+			'posts_per_page' => $per_page,
 			'paged'          => $current_page,
 			'post__not_in'   => $translated_ids,
 			'orderby'        => 'date',
@@ -153,8 +164,8 @@ public function prepare_items(): void {
 		$this->set_pagination_args(
 			array(
 				'total_items' => $total,
-				'per_page'    => self::PER_PAGE,
-				'total_pages' => (int) ceil( $total / self::PER_PAGE ),
+				'per_page'    => $per_page,
+				'total_pages' => $per_page > 0 ? (int) ceil( $total / $per_page ) : 0,
 			)
 		);
 	}