Handles importer uploading and adds attachment.

function wp_import_handle_upload() {
	if ( ! isset( $_FILES['import'] ) ) {
		return array(
			'error' => sprintf(
				/* translators: 1: php.ini, 2: post_max_size, 3: upload_max_filesize */
				__( 'File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your %1$s file or by %2$s being defined as smaller than %3$s in %1$s.' ),
				'php.ini',
				'post_max_size',
				'upload_max_filesize'
			),
		);
	}

	$overrides                 = array(
		'test_form' => false,
		'test_type' => false,
	);
	$_FILES['import']['name'] .= '.txt';
	$upload                    = wp_handle_upload( $_FILES['import'], $overrides );

	if ( isset( $upload['error'] ) ) {
		return $upload;
	}

	// Construct the attachment array.
	$attachment = array(
		'post_title'     => wp_basename( $upload['file'] ),
		'post_content'   => $upload['url'],
		'post_mime_type' => $upload['type'],
		'guid'           => $upload['url'],
		'context'        => 'import',
		'post_status'    => 'private',
	);

	// Save the data.
	$id = wp_insert_attachment( $attachment, $upload['file'] );

	/*
	 * Schedule a cleanup for one day from now in case of failed
	 * import or missing wp_import_cleanup() call.
	 */
	wp_schedule_single_event( time() + DAY_IN_SECONDS, 'importer_scheduled_cleanup', array( $id ) );

	return array(
		'file' => $upload['file'],
		'id'   => $id,
	);
}