protected function expand_data( $data ) {
		$data = apply_filters( 'woocommerce_product_importer_pre_expand_data', $data );

		// Images field maps to image and gallery id fields.
		if ( isset( $data['images'] ) ) {
			$images               = $data['images'];
			$data['raw_image_id'] = array_shift( $images );

			if ( ! empty( $images ) ) {
				$data['raw_gallery_image_ids'] = $images;
			}
			unset( $data['images'] );
		}

		// Type, virtual and downloadable are all stored in the same column.
		if ( isset( $data['type'] ) ) {
			$data['type']         = array_map( 'strtolower', $data['type'] );
			$data['virtual']      = in_array( 'virtual', $data['type'], true );
			$data['downloadable'] = in_array( 'downloadable', $data['type'], true );

			// Convert type to string.
			$data['type'] = current( array_diff( $data['type'], array( 'virtual', 'downloadable' ) ) );

			if ( ! $data['type'] ) {
				$data['type'] = 'simple';
			}
		}

		// Status is mapped from a special published field.
		if ( isset( $data['published'] ) ) {
			$statuses       = array(
				-1 => 'draft',
				0  => 'private',
				1  => 'publish',
			);
			$data['status'] = isset( $statuses[ $data['published'] ] ) ? $statuses[ $data['published'] ] : -1;

			unset( $data['published'] );
		}

		if ( isset( $data['stock_quantity'] ) ) {
			if ( '' === $data['stock_quantity'] ) {
				$data['manage_stock'] = false;
				$data['stock_status'] = isset( $data['stock_status'] ) ? $data['stock_status'] : true;
			} else {
				$data['manage_stock'] = true;
			}
		}

		// Stock is bool or 'backorder'.
		if ( isset( $data['stock_status'] ) ) {
			if ( 'backorder' === $data['stock_status'] ) {
				$data['stock_status'] = 'onbackorder';
			} else {
				$data['stock_status'] = $data['stock_status'] ? 'instock' : 'outofstock';
			}
		}

		// Prepare grouped products.
		if ( isset( $data['grouped_products'] ) ) {
			$data['children'] = $data['grouped_products'];
			unset( $data['grouped_products'] );
		}

		// Tag ids.
		if ( isset( $data['tag_ids_spaces'] ) ) {
			$data['tag_ids'] = $data['tag_ids_spaces'];
			unset( $data['tag_ids_spaces'] );
		}

		// Handle special column names which span multiple columns.
		$attributes = array();
		$downloads  = array();
		$meta_data  = array();

		foreach ( $data as $key => $value ) {
			if ( $this->starts_with( $key, 'attributes:name' ) ) {
				if ( ! empty( $value ) ) {
					$attributes[ str_replace( 'attributes:name', '', $key ) ]['name'] = $value;
				}
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'attributes:value' ) ) {
				$attributes[ str_replace( 'attributes:value', '', $key ) ]['value'] = $value;
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'attributes:taxonomy' ) ) {
				$attributes[ str_replace( 'attributes:taxonomy', '', $key ) ]['taxonomy'] = wc_string_to_bool( $value );
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'attributes:visible' ) ) {
				$attributes[ str_replace( 'attributes:visible', '', $key ) ]['visible'] = wc_string_to_bool( $value );
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'attributes:default' ) ) {
				if ( ! empty( $value ) ) {
					$attributes[ str_replace( 'attributes:default', '', $key ) ]['default'] = $value;
				}
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'downloads:name' ) ) {
				if ( ! empty( $value ) ) {
					$downloads[ str_replace( 'downloads:name', '', $key ) ]['name'] = $value;
				}
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'downloads:url' ) ) {
				if ( ! empty( $value ) ) {
					$downloads[ str_replace( 'downloads:url', '', $key ) ]['url'] = $value;
				}
				unset( $data[ $key ] );

			} elseif ( $this->starts_with( $key, 'meta:' ) ) {
				$meta_data[] = array(
					'key'   => str_replace( 'meta:', '', $key ),
					'value' => $value,
				);
				unset( $data[ $key ] );
			}
		}

		if ( ! empty( $attributes ) ) {
			// Remove empty attributes and clear indexes.
			foreach ( $attributes as $attribute ) {
				if ( empty( $attribute['name'] ) ) {
					continue;
				}

				$data['raw_attributes'][] = $attribute;
			}
		}

		if ( ! empty( $downloads ) ) {
			$data['downloads'] = array();

			foreach ( $downloads as $key => $file ) {
				if ( empty( $file['url'] ) ) {
					continue;
				}

				$data['downloads'][] = array(
					'name' => $file['name'] ? $file['name'] : wc_get_filename_from_url( $file['url'] ),
					'file' => $file['url'],
				);
			}
		}

		if ( ! empty( $meta_data ) ) {
			$data['meta_data'] = $meta_data;
		}

		return $data;
	}