Add pagination header for the campaign endpoint

src/API/Google/AdsCampaign.php

@@ -102,11 +102,12 @@ public function __construct( GoogleAdsClient $client, AdsCampaignBudget $budget,
 	 * @param bool  $exclude_removed Exclude removed campaigns (default true).
 	 * @param bool  $fetch_criterion Combine the campaign data with criterion data (default true).
 	 * @param array $args Arguments for the Ads Campaign Query for example: per_page for limiting the number of results.
+	 * @param bool  $return_pagination_params Whether to return pagination params (default false).
 	 *
 	 * @return array
 	 * @throws ExceptionWithResponseData When an ApiException is caught.
 	 */
-	public function get_campaigns( bool $exclude_removed = true, bool $fetch_criterion = true, $args = [] ): array {
+	public function get_campaigns( bool $exclude_removed = true, bool $fetch_criterion = true, $args = [], $return_pagination_params = false ): array {
 		try {
 			$query = ( new AdsCampaignQuery( $args ) )->set_client( $this->client, $this->options->get_ads_id() );
 
@@ -118,7 +119,10 @@ public function get_campaigns( bool $exclude_removed = true, bool $fetch_criteri
 			$campaign_results    = $query->get_results();
 			$converted_campaigns = [];
 
-			foreach ( $campaign_results->getPage()->getIterator()  as $row ) {
+			/** @var Page $page */
+			$page = $campaign_results->getPage();
+
+			foreach ( $page->getIterator()  as $row ) {
 				++$campaign_count;
 				$campaign                               = $this->convert_campaign( $row );
 				$converted_campaigns[ $campaign['id'] ] = $campaign;
@@ -137,6 +141,16 @@ public function get_campaigns( bool $exclude_removed = true, bool $fetch_criteri
 				$converted_campaigns = $this->combine_campaigns_and_campaign_criterion_results( $converted_campaigns );
 			}
 
+			if ( $return_pagination_params ) {
+				// Total results across all pages.
+				$total_results   = $page->getResponseObject()->getTotalResultsCount();
+				$next_page_token = $page->getNextPageToken();
+				return [
+					'campaigns'       => array_values( $converted_campaigns ),
+					'total_results'   => $total_results,
+					'next_page_token' => $next_page_token,
+				];
+			}
 			return array_values( $converted_campaigns );
 		} catch ( ApiException $e ) {
 			do_action( 'woocommerce_gla_ads_client_exception', $e, __METHOD__ );

src/API/Google/Query/AdsQuery.php

@@ -91,6 +91,8 @@ protected function query_results() {
 		}
 
 		$request = new SearchGoogleAdsRequest();
+		// Allow us to get the total number of results for pagination.
+		$request->setReturnTotalResultsCount( true );
 
 		if ( ! empty( $this->search_args['pageSize'] ) ) {
 			$request->setPageSize( $this->search_args['pageSize'] );

src/API/Site/Controllers/Ads/CampaignController.php

@@ -99,15 +99,33 @@ public function register_routes(): void {
 	protected function get_campaigns_callback(): callable {
 		return function ( Request $request ) {
 			try {
-				$exclude_removed = $request->get_param( 'exclude_removed' );
+				$exclude_removed          = $request->get_param( 'exclude_removed' );
+				$return_pagination_params = true;
+				$campaign_data            = $this->ads_campaign->get_campaigns( $exclude_removed, true, $request->get_params(), $return_pagination_params );
 
-				return array_map(
+				$campaigns = array_map(
 					function ( $campaign ) use ( $request ) {
 						$data = $this->prepare_item_for_response( $campaign, $request );
 						return $this->prepare_response_for_collection( $data );
 					},
-					$this->ads_campaign->get_campaigns( $exclude_removed, true, $request->get_params() )
+					$campaign_data['campaigns']
 				);
+
+				$response = rest_ensure_response( $campaigns );
+
+				$total_campaigns = (int) $campaign_data['total_results'];
+				$response->header( 'X-WP-Total', $total_campaigns );
+				// If per_page is not set, then set it to total number of campaigns.
+				$per_page  = $request->get_param( 'per_page' ) ?: $total_campaigns;
+				$max_pages = $per_page > 0 ? ceil( $total_campaigns / $per_page ) : 1;
+				$response->header( 'X-WP-TotalPages', (int) $max_pages );
+
+				if ( ! empty( $campaign_data['next_page_token'] ) ) {
+					$response->header( 'X-GLA-NextPageToken', $campaign_data['next_page_token'] );
+				}
+
+				return $response;
+
 			} catch ( Exception $e ) {
 				return $this->response_from_exception( $e );
 			}