public static function process_batch_request() {
		// Batch ID.
		$batch_id = isset( $_REQUEST['batch_id'] ) ? sanitize_key( $_REQUEST['batch_id'] ) : false;

		if ( ! $batch_id ) {
			wp_send_json_error(
				array(
					'error' => __( 'A batch process ID must be present to continue.', 'popup-maker' ),
				)
			);
		}

		// Nonce.
		if ( ! isset( $_REQUEST['nonce'] ) || ( isset( $_REQUEST['nonce'] ) && false === wp_verify_nonce( $_REQUEST['nonce'], "{$batch_id}_step_nonce" ) ) ) {
			wp_send_json_error(
				array(
					'error' => __( 'You do not have permission to initiate this request. Contact an administrator for more information.', 'popup-maker' ),
				)
			);
		}

		// Attempt to retrieve the batch attributes from memory.
		$batch = PUM_Batch_Process_Registry::instance()->get( $batch_id );

		if ( false === $batch ) {
			wp_send_json_error(
				array(
					'error' => sprintf( __( '%s is an invalid batch process ID.', 'popup-maker' ), esc_html( $_REQUEST['batch_id'] ) ),
				)
			);
		}

		$class      = isset( $batch['class'] ) ? sanitize_text_field( $batch['class'] ) : '';
		$class_file = isset( $batch['file'] ) ? $batch['file'] : '';

		if ( empty( $class_file ) || ! file_exists( $class_file ) ) {
			wp_send_json_error(
				array(
					'error' => sprintf( __( 'An invalid file path is registered for the %1$s batch process handler.', 'popup-maker' ), "<code>{$batch_id}</code>" ),
				)
			);
		} else {
			require_once $class_file;
		}

		if ( empty( $class ) || ! class_exists( $class ) ) {
			wp_send_json_error(
				array(
					'error' => sprintf( __( '%1$s is an invalid handler for the %2$s batch process. Please try again.', 'popup-maker' ), "<code>{$class}</code>", "<code>{$batch_id}</code>" ),
				)
			);
		}

		$step = sanitize_text_field( $_REQUEST['step'] );

		/**
		 * Instantiate the batch class.
		 *
		 * @var PUM_Interface_Batch_Exporter|PUM_Interface_Batch_Process|PUM_Interface_Batch_PrefetchProcess $process
		 */
		if ( isset( $_REQUEST['data']['upload']['file'] ) ) {

			// If this is an import, instantiate with the file and step.
			$file    = sanitize_text_field( $_REQUEST['data']['upload']['file'] );
			$process = new $class( $file, $step );

		} else {

			// Otherwise just the step.
			$process = new $class( $step );

		}

		// Garbage collect any old temporary data.
		// TODO Should this be here? Likely here to prevent case ajax passes step 1 without resetting process counts?
		if ( $step < 2 ) {
			$process->finish();
		}

		$using_prefetch = ( $process instanceof PUM_Interface_Batch_PrefetchProcess );

		// Handle pre-fetching data.
		if ( $using_prefetch ) {
			// Initialize any data needed to process a step.
			$data = isset( $_REQUEST['form'] ) ? $_REQUEST['form'] : array();

			$process->init( $data );
			$process->pre_fetch();
		}

		/** @var int|string|WP_Error $step */
		$step = $process->process_step();

		if ( is_wp_error( $step ) ) {
			wp_send_json_error( $step );
		} else {
			$response_data = array( 'step' => $step );

			// Map fields if this is an import.
			if ( isset( $process->field_mapping ) && ( $process instanceof PUM_Interface_CSV_Importer ) ) {
				$response_data['columns'] = $process->get_columns();
				$response_data['mapping'] = $process->field_mapping;
			}

			// Finish and set the status flag if done.
			if ( 'done' === $step ) {
				$response_data['done']    = true;
				$response_data['message'] = $process->get_message( 'done' );

				// If this is an export class and not an empty export, send the download URL.
				if ( method_exists( $process, 'can_export' ) ) {

					if ( ! $process->is_empty ) {
						$response_data['url'] = pum_admin_url(
							'tools',
							array(
								'step'       => $step,
								'nonce'      => wp_create_nonce( 'pum-batch-export' ),
								'batch_id'   => $batch_id,
								'pum_action' => 'download_batch_export',
							)
						);
					}
				}

				// Once all calculations have finished, run cleanup.
				$process->finish();
			} else {
				$response_data['done']       = false;
				$response_data['percentage'] = $process->get_percentage_complete();
			}

			wp_send_json_success( $response_data );
		}

	}