Normalize variable as an expanding window

Hi,

I would like to normalize the price of the following as an expanding window taking into account all information up to time t (but not after t, to avoid look-ahead bias). So far, I have the code that takes into account the entire dataset, and hence, induces a look-ahead bias. Can someone help me edit the code? Thanks

Code:

clear
local ticker "BTC-USD"
getsymbols `ticker', fm(1) fd(1) fy(2012) lm(12) frequency(d) price(adjclose) yahoo clear
keep period p_adjclose_BTC_USD

* Normalization:
local To_Norm p_adjclose_BTC_USD
foreach var in `To_Norm' {
    sum `var', meanonly 
    gen n_`var' = (`var' - r(min)) / (r(max) - r(min)) 
}