complex formula/array, Column Matching, and Data formatting and Populating

A C E G H

20 AB1 0 57
30 AB2 0 91
0 AB3 0 0
9 AB4 21 6
4 AB5 31 0
120 AB6 120 2
0 AB7 0 7
1 AB8 1 12
25 AB9 25 200
10 AB10 6 165


When comparing columns A, E and G,
I want column H to populate based on the following conditions:-

Priority given to value in column D.
If value in Column D is Zero, the Priority should be given to Column A
If Column A is also Zero, the value from Column G should populate in column H

I hope I have clarified my Question.

I think the conditions are making it more complex. Thats where I am stuck.