How to create Eway payment gateway for Membership plugin?

I am a Developer & I am using WPMU Membership Plugin.

I need to create Eway Payment Gateway (using Eway Shared Payments API)for this plugin.

I have already read so many posts on the forum where many have suggested to use PayPal Payments Standard Gateway as a reference to create a custom gateway.

But still no one has described an approach to achieve the same.
I mean no one has explained what needs to be changed in the gateway code technically.

I know I need to change a few things as per the Eway API but still a detailed approach will be more appreciated.

Thanks in Advance.