Pandas replace zero as the nearest average non-zero value

I have a dataframe:

 df = pd.DataFrame({'A':[0,0,15,0,0,12,0,0,0,5]})

And I want to replace the 0 value with the nearest non zero value,

For example, the first value is 0, then I find the the nearest non-zero value is 15, so I replace it as 15, then the data becomes:[15,0,15,0,0,12,0,0,0,5],

Then for all the value except first one, I need to find the both side of the nearest non-zero value, and average them. So for the second 0, it would be (15+15)/2; And the third zero would be (15+12)/2

I only know how to replace zero to the nearest value by:

df['A'].replace(to_replace=0, method='ffill')0     01     02    153    154    155    126    127    128    129     5

But the first two zero value cannot be replaced, and this way is not getting the average value.