_last_order( $customer_id ) {
		global $wpdb;
		$orders_table = $wpdb->prefix . 'wc_order_stats';

		$last_order = $wpdb->get_var(
			$wpdb->prepare(
				// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared
				"SELECT order_id, date_created_gmt FROM {$orders_table}
				WHERE customer_id = %d
				ORDER BY date_created_gmt DESC, order_id DESC LIMIT 1",
				// phpcs:enable
				$customer_id
			)
		);
		if ( ! $last_order ) {
			return false;
		}
		return wc_get_order( absint( $last_order ) );
	}

	/**
	 * Retrieve the oldest orders made by a customer.
	 *
	 * @param int $customer_id Customer ID.
	 * @return array Orders.
	 */
	public static function get_oldest_orders( $customer_id ) {
		global $wpdb;
		$orders_table                = $wpdb->prefix . 'wc_order_stats';
		$excluded_statuses           = array_map( array( __CLASS__, 'normalize_order_status' ), self::get_excluded_report_order_statuses() );
		$excluded_statuses_condition = '';
		if ( ! empty( $excluded_statuses ) ) {
			$excluded_statuses_str       = implode( "','", $excluded_statuses );
			$excluded_statuses_condition = "AND status NOT IN ('{$excluded_statuses_str}')";
		}

		return $wpdb->get_results(
			$wpdb->prepare(
				// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
				"SELECT order_id, date_created FROM {$orders_table} WHERE customer_id = %d {$excluded_statuses_condition} ORDER BY date_created, order_id ASC LIMIT 2",
				$customer_id
			)
		);
	}

	/**
	 * Retrieve the amount of orders made by a customer.
	 *
	 * @param int $customer_id Customer ID.
	 * @return int|null Amount of orders for customer or null on failure.
	 */
	public static function get_order_count( $customer_id ) {
		global $wpdb;
		$customer_id = absint( $customer_id );

		if ( 0 === $customer_id ) {
			return null;
		}

		$result = $wpdb->get_var(
			$wpdb->prepare(
				"SELECT COUNT( order_id ) FROM {$wpdb->prefix}wc_order_stats WHERE customer_id = %d",
				$customer_id
			)
		);

		if ( is_null( $result ) ) {
			return null;
		}

		return (int) $result;
	}

	/**
	 * Update the database with customer data.
	 *
	 * @param int $user_id WP User ID to update customer data for.
	 * @return int|bool|null Number or rows modified or false on failure.
	 */
	public static function update_registered_customer( $user_id ) {
		global $wpdb;

		$customer = new \WC_Customer( $user_id );

		if ( ! self::is_valid_customer( $user_id ) ) {
			return false;
		}

		$last_order = $customer->get_last_order();

		if ( ! $last_order ) {
			$first_name = get_user_meta( $user_id, 'first_name', true );
			$last_name  = get_user_meta( $user_id, 'last_name', true );
		} else {
			$first_name = $last_order->get_customer_first_name();
			$last_name  = $last_order->get_customer_last_name();
		}

		$last_active = $customer->get_meta( 'wc_last_active', true, 'edit' );
		$data        = array(
			'user_id'          => $user_id,
			'username'         => $customer->get_username( 'edit' ),
			'first_name'       => $first_name,
			'last_name'        => $last_name,
			'email'            => $customer->get_email( 'edit' ),
			'city'             => $customer->get_billing_city( 'edit' ),
			'state'            => $customer->get_billing_state( 'edit' ),
			'postcode'         => $customer->get_billing_postcode( 'edit' ),
			'country'          => $customer->get_billing_country( 'edit' ),
			'date_registered'  => $customer->get_date_created( 'edit' )->date( TimeInterval::$sql_datetime_format ),
			'date_last_active' => $last_active ? gmdate( 'Y-m-d H:i:s', $last_active ) : null,
		);
		$format      = array(
			'%d',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
			'%s',
		);

		$customer_id = self::get_customer_id_by_user_id( $user_id );

		if ( $customer_id ) {
			// Preserve customer_id for existing user_id.
			$data['customer_id'] = $customer_id;
			$format[]            = '%d';
		}

		$results = $wpdb->replace( self::get_db_table_name(), $data, $format );

		/**
		 * Fires when customser's reports are updated.
		 *
		 * @param int $customer_id Customer ID.
		 */
		do_action( 'woocommerce_analytics_update_customer', $customer_id );

		ReportsCache::invalidate();

		return $results;
	}

	/**
	 * Check if a user ID is a valid customer or other user role with past orders.
	 *
	 * @param int $user_id User ID.
	 * @return bool
	 */
	protected static function is_valid_customer( $user_id ) {
		$customer = new \WC_Customer( $user_id );

		if ( absint( $customer->get_id() ) !== absint( $user_id ) ) {
			return false;
		}

		$customer_roles = (array) apply_filters( 'woocommerce_analytics_customer_roles', array( 'customer' ) );
		if ( $customer->get_order_count() < 1 && ! in_array( $customer->get_role(), $customer_roles, true ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Delete a customer lookup row.
	 *
	 * @param int $customer_id Customer ID.
	 */
	public static function delete_customer( $customer_id ) {
		global $wpdb;

		$customer_id = (int) $customer_id;
		$num_deleted = $wpdb->delete( self::get_db_table_name(), array( 'customer_id' => $customer_id ) );

		if ( $num_deleted ) {
			/**
			 * Fires when a customer is deleted.
			 *
			 * @param int $order_id Order ID.
			 */
			do_action( 'woocommerce_analytics_delete_customer', $customer_id );

			ReportsCache::invalidate();
		}
	}

	/**
	 * Delete a customer lookup row by WordPress User ID.
	 *
	 * @param int $user_id WordPress User ID.
	 */
	public static function delete_customer_by_user_id( $user_id ) {
		global $wpdb;

		$user_id     = (int) $user_id;
		$num_deleted = $wpdb->delete( self::get_db_table_name(), array( 'user_id' => $user_id ) );

		if ( $num_deleted ) {
			ReportsCache::invalidate();
		}
	}

	/**
	 * Initialize query objects.
	 */
	protected function initialize_queries() {
		$this->clear_all_clauses();
		$table_name     = self::get_db_table_name();
		$this->subquery = new SqlQuery( $this->context . '_subquery' );
		$this->subquery->add_sql_clause( 'from', $table_name );
		$this->subquery->add_sql_clause( 'select', "{$table_name}.customer_id" );
		$this->subquery->add_sql_clause( 'group_by', "{$table_name}.customer_id" );
	}
}