Calculate a Running Total as a variable which Resets based on a condition

Hi Members,

Im new to the world of PowerBI and I need help with the following Running Total I need to calculate in DAX.

Definition -> BalancePick = OpeningStockPosition + POs Pick - Demand

I want to calculate a Running Total on BalancePick by Date and Item (StockAfter Picks).

So My Current DAX Works well in the instance we have a large OpeningStockPosition and plentiful POs Pick on certain Dates:

Item Example 37816 where DAX Works

Item Example 37916 where DAX doesnt work

It doesnt work as No Opening Stock Position, plus not enough POs Pick.

Currently:

What I actually need StockAfter Picks to show (Yellow Highlights):

So what I actually need DAX to do is compute a running total between the current row and row above and check if its negative set to zero or its fine, then use that in the next running total computation.

In Variable Form

Let Opening Stock Postion= A

Let POs Pick = B

Let Demand = C

StockAfter Picks Row 1 = IF( A(1)+B(1)-C(1) <0 ,0 A(1)+B(1)-C(1) ) 

Let StockAfter Picks Row 1 = NewStockPosition(1)

StockAfter Picks Row 2 = IF( NewStockPostion(1) +B(2)-C(2) <0 ,0 ,NewStockPostion(1)+B(2)-C(2) )

Let StockAfter Picks Row 2 = NewStockPosition(2)

And it iterates so on based on the date column and item number column.