use Data::Dumper;
use XML::LibXML;

my $xml = q|<?xml version="1.0"?>
<root><order><id>359</id><order_number>359</order_number><created_at>2019-03-28 10:33:06</created_at>...etc...|;

my @top_level = qw(
	order_number
	created_at
	total
	total_shipping
	total_discount
	customer_id
	currency
);

my @nested = qw(
	shipping_lines
	billing_address
	shipping_address
	fee_lines
);

my @orders;

my $doc = XML::LibXML->load_xml(string => $xml);

my @nodes = $doc->findnodes('//order');

for my $node (@nodes) {
	my %order;
	# get the top level nodes
	for my $name ( @top_level ) {
		$order{$name} = $node->findvalue($name);
	}
	# get the nested nodes
	for my $name ( @nested ) {
		my ($elem) = $node->findnodes($name);
		$order{$name} = process_nested($elem);
	}
	# special case for line_items node
	my ($line_items) = $node->findnodes('line_items');
	$order{'line_items'} = process_line_items( $line_items );
	
	push( @orders, \%order );
}

print Dumper(\@orders);


sub process_nested {
	my ($node) = @_;
	my %item;
	my $elem = $node->firstChild or return '';
	$item{ $elem->nodeName } = $elem->textContent;
	while ( my $next = $elem->nextSibling )  {
		$item{ $next->nodeName } = $next->textContent;
		$elem = $next;
	}
	return \%item;
}

sub process_line_items {
	my ($node) = @_;
	my @items;
	my @id_nodes = $node->findnodes('id') or return '';
	for my $id_node ( @id_nodes ) {
		my $elem = $id_node;
		my %item = ( id => $elem->textContent );
		while ( my $next = $elem->nextSibling )  {
			my $name = $next->nodeName;
			# exit if we have reached the next item
			last if $name eq 'id';
			$item{$name} = $next->textContent;
			$elem = $next;
		}
		push(@items, \%item);
	}
	return \@items;
}