How to create custom auto generated item description through EFF values based on the user item type?

Summary:

How can i create a custom and unique auto generated item description through EFF values based on the user item type? Catch is that the number of values to be used in the description differs as per the item type. So some descriptions might require 4 values and some might need 2 only. But if the user doesn't pass the value for one of the EFF where 4 values are required for description, it should throw an error.

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