XML Reference Guide

At this point, we've built a Perl script that sends a request to the Amazon Electronic Commerce Service and gets information on the first 10 items on your wish list. Now we want to turn that script into a Movable Type plug-in that displays a random item on that list when the pages built or dynamically displayed. To do that, will need to work out how to select one random item, and then convert the script into a plug-in.

First, the logic.

So far, we've displayed all of the first 10 items on the list. To display a single item, we need to access the items as an array:

#!/usr/local/bin/perl

use SOAP::Lite;

my $lookup = SOAP::Lite->uri('http://webservices.amazon.com/AWSECommerceService/2005-07-26')->proxy('http://soap.amazon.com/onca/soap?Service=AWSECommerceService');


my $SubscriptionIdElement = SOAP::Data->name('SubscriptionId')
                              ->value('0NQJY4BXVZP3SFWWPZG2');
my $AssociateTagElement = SOAP::Data->name('AssociateTag')
                            ->value('thevanguardsc-20');

my $ListIdElement = SOAP::Data->name('ListId')
                              ->value('4M6WEGGRFLZO');
my $ListTypeElement = SOAP::Data->name('ListType')
                            ->value('WishList');
my $ResponseGroupElement = SOAP::Data->name('ResponseGroup')
                            ->value('Medium');
my $RequestElementType = SOAP::Data->value($ListIdElement, $ListTypeElement, $ResponseGroupElement);

my $RequestElement = SOAP::Data->name('Request')
                            ->value($RequestElementType);

my $ListLookupRequest = SOAP::Data->value($SubscriptionIdElement, $RequestElement);


my $response =  $lookup->ListLookup($ListLookupRequest);


print "RequestProcessingTime = ";
print $response->dataof('//RequestProcessingTime')->value;
print "\n";

      @itemarray = $response->valueof('//Item');
      my $item = $itemarray[7];

      print "<p><a href='" . $item->{DetailPageURL} . "'>";
      print "<img src='" . $item->{SmallImage}->{URL} . "' />";
      print "</a>";
      print "<br />";
      print $item->{ItemAttributes}->{Title};
      print "</p>\n";

Notice that I've also changed the output to match the HTML we'll ultimately want to display, so the resulting text looks something like this:

RequestProcessingTime = 0.948960065841675
<a href='http://www.amazon.com/exec/obidos/redirect?tag=ws%26link_code=sp1%26camp=2025%26creative=165953%26path=http://www.amazon.com/gp/redirect.html%253fASIN=0764549103%2526tag=ws%2526lcode=sp1%2526cID=2025%2526ccmID=165953%2526location=/o/ASIN/0764549103%25253FSubscriptionId=0NQJY4BXVZP3SFWWPZG2%252526coliid=IZD3O6ZXGY3OC%252526colid=4M6WEGGRFLZO'><img src='https://images.amazon.com/images/P/0764549103.01._SCTHUMBZZZ_.jpg' /></a><br />UML Weekend Crash Course</p>

As for which item to display, we need a number between one and the number of items on the list:

...
my $response =  $lookup->ListLookup($ListLookupRequest);


print "RequestProcessingTime = ";
print $response->dataof('//RequestProcessingTime')->value;

print "\n";

      $totalItems = 24;
      $thisItem = sprintf("%d", rand $totalItems);

      print "Requesting item " . $thisItem . "\n";

      @itemarray = $response->valueof('//Item');
      my $item = $itemarray[$thisItem];
...

Here we're using Perl's rand function to create a fractional number between 0 and the number of items on the list, and then using sprintf to turn it into an integer.

Note that I'm specifying the number of items on the list. We could do a list look up and find out the current size of the list, it's not a good idea for performance reasons. We're already going to significantly slow down the rebuild process by requiring a Web service call for each page. Two calls would be ridiculous. In fact, according to Amazon's terms of service, we need to limit our activity to a maximum of one call per second:

...
      print "<br />";
      print $item->{ItemAttributes}->{Title};
      print "</p>\n";

      sleep(1);
      print "Ready for the next one.\n";

Now we need to make sure the target item is available. Each page includes 10 items, so we need to add the ProductPage parameter to our request:

#!/usr/local/bin/perl
use lib qw(/home/nicholaschase/www/cgi-bin/lib/5.6.1/i386-linux
/home/nicholaschase/www/cgi-bin/lib/site_perl/5.6.1);

use SOAP::Lite;

      $totalItems = 24;
      $thisItem = sprintf("%.0f", rand $totalItems);

      print "Requesting item " . $thisItem . "\n";

      $rawProductPage = ($thisItem/10);
      $productPage = sprintf("%.0f", $rawProductPage);

      if ($rawProductPage - $productPage > 0) {
         $productPage = $productPage + 1;
      }

my $lookup = SOAP::Lite->uri('http://webservices.amazon.com/AWSECommerceService/2005-07-26')->proxy('http://soap.amazon.com/onca/soap?Service=AWSECommerceService');

my $SubscriptionIdElement = SOAP::Data->name('SubscriptionId')
                              ->value('0NQJY4BXVZP3SFWWPZG2');
my $AssociateTagElement = SOAP::Data->name('AssociateTag')
                            ->value('thevanguardsc-20');
my $ListIdElement = SOAP::Data->name('ListId')
                              ->value('4M6WEGGRFLZO');

my $ListTypeElement = SOAP::Data->name('ListType')
                            ->value('WishList');
my $ResponseGroupElement = SOAP::Data->name('ResponseGroup')
                            ->value('Medium');
my $ProductPageElement = SOAP::Data->name('ProductPage')
                            ->value($productPage);

my $RequestElementType = SOAP::Data->value($ListIdElement, $ListTypeElement, $ResponseGroupElement, $ProductPageElement);
my $RequestElement = SOAP::Data->name('Request')
                               ->value($RequestElementType);
my $ListLookupRequest = SOAP::Data->value($SubscriptionIdElement, $RequestElement);


my $response =  $lookup->ListLookup($ListLookupRequest);


print "RequestProcessingTime = ";
print $response->dataof('//RequestProcessingTime')->value;

print "\n";
print "Product page =".$productPage."\n";
         
      $thisArrayItem = $thisItem - (($productPage-1) * 10) -1;
      
      print "Requesting array item " . $thisArrayItem . "\n";

      @itemarray = $response->valueof('//Item');
      my $item = $itemarray[$thisArrayItem];
...

Now when we run the script, will get a different item each time:

[nicholaschase@spinel cgi-bin]$ perl amz2.cgi
Requesting item 3
RequestProcessingTime = 3.87524199485779
Product page = 1
Requesting array item 2

Evita: The Complete Motion Picture Music Soundtrack
Ready for the next one.
[nicholaschase@spinel cgi-bin]$ perl amz2.cgi
Requesting item 17
RequestProcessingTime = 0.854296207427979
Product page = 2
Requesting array item 6

The Pleasure of Finding Things Out and the Meaning of It All
Ready for the next one.

At this point, we're finally ready to turn this thing into a plug-in. To do that, copy the Perl script into your Movable Type plugins directory and strip out the debugging information. Next, add a package declaration and the template context:

#!/usr/local/bin/perl

package MT::Plugin::AmazonWishList;

use SOAP::Lite;
use MT::Template::Context;
MT::Template::Context->add_tag(AmazonWishList => \&wishlist);

sub wishlist() {

      $totalItems = 24;
      $thisItem = sprintf("%.0f", rand $totalItems);

      $rawProductPage = ($thisItem/10);
      $productPage = sprintf("%.0f", $rawProductPage);
...
      $thisArrayItem = $thisItem - (($productPage-1) * 10) -1;   

      @itemarray = $response->valueof('//Item');
      my $item = $itemarray[$thisArrayItem];


      $returnString = "<p><a href='" . $item->{DetailPageURL} . "'>";
      $returnString = $returnString . "<img border='0' src='" . $item->{SmallIma
ge}->{URL} . "' />";
      $returnString = $returnString . "<br />";
      $returnString = $returnString . $item->{ItemAttributes}->{Title};
      $returnString = $returnString . "</a>";

      $returnString = $returnString . "</p>\n";

      sleep(1);

      return "Results are ".$returnString;

}

What we're actually doing here is associating a tag, which we'll add to the template, with the Perl subroutine. As such, we've also made a subroutine out of our code, returning the final string instead of directly printing it.

Now we need to add the tag to our page. In your template, add the MTAmazonWishList tag:

This is a test.  It is only a test. 
<MTAmazonWishList />

Now first of all, I've obviously created a simple template for testing here. Second, notice that while we mapped the subroutine to the AmazonWishList tag, when we actually use it it becomes the MTAmazonWishList tag.

Finally, we rebuild the page, and see the results.

Our final task is to make it possible to pass in user-configurable information, such as the list ID. We can do that by adding attributes to the tag:

This is a test.  It is only a test. 
<MTAmazonWishList totalItems="24" token="0NQJY4BXVZP3SFWWPZG2" 
                     listId="4M6WEGGRFLZO" associateTag="thevanguardsc-20" />

We can then read the attributes from the plug-in, which receives them as an argument:

#!/usr/local/bin/perl
package MT::Plugin::AmazonWishList;

use SOAP::Lite;
use MT::Template::Context;
MT::Template::Context->add_tag(AmazonWishList => \&wishlist); 

sub wishlist() {

      my $context = shift;
      my $attributes = shift;
      $totalItems = $attributes->{totalItems};
      $token = $attributes->{token};
      $associateTag = $attributes->{associateTag};
      $listId = $attributes->{listId}

      $thisItem = sprintf("%.0f", rand $totalItems);

      $rawProductPage = ($thisItem/10);
      $productPage = sprintf("%.0f", $rawProductPage);
      
      if ($rawProductPage - $productPage > 0) {
         $productPage = $productPage + 1;
      }

my $lookup = SOAP::Lite->uri('http://webservices.amazon.com/AWSECommerceService/
2005-07-26')->proxy('http://soap.amazon.com/onca/soap?Service=AWSECommerceServic
e');


my $SubscriptionIdElement = SOAP::Data->name('SubscriptionId')
                                      ->value($token);
my $AssociateTagElement = SOAP::Data->name('AssociateTag')
                                      ->value($associateTag);

my $ListIdElement = SOAP::Data->name('ListId')
                              ->value($listId);
my $ListTypeElement = SOAP::Data->name('ListType')
                            ->value('WishList');
...

You can also use these attributes to set styles for the final output, or to determine other features such as surrounding text. And now, because the plugin's been generalized, you can simply install the Perl script on any Movable Type installation and go from there.