[Python] Pandas: set all values that are <= 0 to the maximum value in a column by group, but...

I am trying to set all values that are <= 0, by group, to the maximum value in that group, but only after the last positive value. That is, all values <=0 in the group that come before the last positive value must be ignored. Example:

data = {'group':['A', 'A', 'A', 'A', 'A', 'B', 'B',
'B', 'B', 'B', 'B', 'C', 'C', 'C', 'C', 'C'],
'value':[3, 0, 8, 7, 0, -1, 0, 9, -2, 0, 0, 2, 0, 5, 0, 1]}
df = pd.DataFrame(data)
df

group value
0 A 3
1 A 0
2 A 8
3 A 7
4 A 0
5 B -1
6 B 0
7 B 9
8 B -2
9 B 0
10 B 0
11 C 2
12 C 0
13 C 5
14 C 0
15 C 1


and the result must be:

group value
0 A 3
1 A 0
2 A 8
3 A 7
4 A 8
5 B -1
6 B 0
7 B 9
8 B 9
9 B 9
10 B 9
11 C 2
12 C 0
13 C 5
14 C 0
15 C 1


Thanks to advise

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