WP_REST_Terms_Controller::get_items() WordPress Method

	public function get_items( $request ) {

		// Retrieve the list of registered collection query parameters.
		$registered = $this->get_collection_params();

		/*
		 * This array defines mappings between public API query parameters whose
		 * values are accepted as-passed, and their internal WP_Query parameter
		 * name equivalents (some are the same). Only values which are also
		 * present in $registered will be set.
		 */
		$parameter_mappings = array(
			'exclude'    => 'exclude',
			'include'    => 'include',
			'order'      => 'order',
			'orderby'    => 'orderby',
			'post'       => 'post',
			'hide_empty' => 'hide_empty',
			'per_page'   => 'number',
			'search'     => 'search',
			'slug'       => 'slug',
		);

		$prepared_args = array( 'taxonomy' => $this->taxonomy );

		/*
		 * For each known parameter which is both registered and present in the request,
		 * set the parameter's value on the query $prepared_args.
		 */
		foreach ( $parameter_mappings as $api_param => $wp_param ) {
			if ( isset( $registered[ $api_param ], $request[ $api_param ] ) ) {
				$prepared_args[ $wp_param ] = $request[ $api_param ];
			}
		}

		if ( isset( $prepared_args['orderby'] ) && isset( $request['orderby'] ) ) {
			$orderby_mappings = array(
				'include_slugs' => 'slug__in',
			);

			if ( isset( $orderby_mappings[ $request['orderby'] ] ) ) {
				$prepared_args['orderby'] = $orderby_mappings[ $request['orderby'] ];
			}
		}

		if ( isset( $registered['offset'] ) && ! empty( $request['offset'] ) ) {
			$prepared_args['offset'] = $request['offset'];
		} else {
			$prepared_args['offset'] = ( $request['page'] - 1 ) * $prepared_args['number'];
		}

		$taxonomy_obj = get_taxonomy( $this->taxonomy );

		if ( $taxonomy_obj->hierarchical && isset( $registered['parent'], $request['parent'] ) ) {
			if ( 0 === $request['parent'] ) {
				// Only query top-level terms.
				$prepared_args['parent'] = 0;
			} else {
				if ( $request['parent'] ) {
					$prepared_args['parent'] = $request['parent'];
				}
			}
		}

		/**
		 * Filters get_terms() arguments when querying terms via the REST API.
		 *
		 * The dynamic portion of the hook name, `$this->taxonomy`, refers to the taxonomy slug.
		 *
		 * Possible hook names include:
		 *
		 *  - `rest_category_query`
		 *  - `rest_post_tag_query`
		 *
		 * Enables adding extra arguments or setting defaults for a terms
		 * collection request.
		 *
		 * @since 4.7.0
		 *
		 * @link /reference/functions/get_terms/
		 *
		 * @param array           $prepared_args Array of arguments for get_terms().
		 * @param WP_REST_Request $request       The REST API request.
		 */
		$prepared_args = apply_filters( "rest_{$this->taxonomy}_query", $prepared_args, $request );

		if ( ! empty( $prepared_args['post'] ) ) {
			$query_result = wp_get_object_terms( $prepared_args['post'], $this->taxonomy, $prepared_args );

			// Used when calling wp_count_terms() below.
			$prepared_args['object_ids'] = $prepared_args['post'];
		} else {
			$query_result = get_terms( $prepared_args );
		}

		$count_args = $prepared_args;

		unset( $count_args['number'], $count_args['offset'] );

		$total_terms = wp_count_terms( $count_args );

		// wp_count_terms() can return a falsey value when the term has no children.
		if ( ! $total_terms ) {
			$total_terms = 0;
		}

		$response = array();

		foreach ( $query_result as $term ) {
			$data       = $this->prepare_item_for_response( $term, $request );
			$response[] = $this->prepare_response_for_collection( $data );
		}

		$response = rest_ensure_response( $response );

		// Store pagination values for headers.
		$per_page = (int) $prepared_args['number'];
		$page     = ceil( ( ( (int) $prepared_args['offset'] ) / $per_page ) + 1 );

		$response->header( 'X-WP-Total', (int) $total_terms );

		$max_pages = ceil( $total_terms / $per_page );

		$response->header( 'X-WP-TotalPages', (int) $max_pages );

		$base = add_query_arg( urlencode_deep( $request->get_query_params() ), rest_url( $this->namespace . '/' . $this->rest_base ) );
		if ( $page > 1 ) {
			$prev_page = $page - 1;

			if ( $prev_page > $max_pages ) {
				$prev_page = $max_pages;
			}

			$prev_link = add_query_arg( 'page', $prev_page, $base );
			$response->link_header( 'prev', $prev_link );
		}
		if ( $max_pages > $page ) {
			$next_page = $page + 1;
			$next_link = add_query_arg( 'page', $next_page, $base );

			$response->link_header( 'next', $next_link );
		}

		return $response;
	}