The concept and logic
TL;DR
Use this addon to create Shipping Methods for Simple Commerce that work with the Australia Post PAC API.
Each Shipping Method you create can include up to one Domestic and up to one International Australia Post Service Code. This addon can create Australia Post-compatible Shipping Methods for you using a command.
Your Simple Commerce Products will need to have package dimensions and weight attributes added.
Australia Post's Postage Assessment Calculator (PAC) allows you to get a quote for any of their services, including both domestic (within Australia) and international (from Australia to overseas) options.
You will need to know your package dimensions and weight for Australia Post's calculator.
This addon attempts to bundle the Products in a customer's Simple Commerce Order in to as few packages as possible while following the Australia Post package size and volume restrictions. Each package gets a quote from the Australia Post PAC, and is summed to give you a total cost for the shipping method.
Because Simple Commerce's shipping methods are simple and singular in nature, for each Australia Post service, you will need to create a new Shipping Method for your Simple Commerce site. Don't worry: this addon has a command to help you do this.
Each Shipping Method can be configured to work for both Domestic and International service codes. This means that you could use "Parcel Post" with one Service Code for Domestic calculations, and one Service Code for International. You can even disable domestic or international costings for a specific Shipping Method too.
For example, let's say you wanted to offer Parcel Post to both Domestic and International customers, and Express Post for Australian customers only, you would need:
A Parcel Post Shipping Method, with two Service Codes - one for Domestic and one for International
An Express Post Shipping Method, with a Domestic Service Code only
It sounds more complicated than it is - and this addon will do the heavy lifting for you. You can use this addon's command to make a new Shipping Method that will work with the Australia Post PAC, and run another command to find the right service codes to use.
If anything goes awry while getting a shipping cost, the Shipping Method will be hidden from the user. This can include:
exceeding Australia Post's restrictions
Australia Post not allowing that service code to the destination location
general API connectivity errors (such as Australia Post being offline, invalid API key, etc)
Don't forget to update your Shipping Method selection view with appropriate handling of the case where there are no shipping methods available.