Conversion of Plsql function to support snowflake - plsql

Question

I need some help here to convert the below oracle function to Snowflake sql. The requirement here is the below code converts the local currency amount to USD for with the specific rate at the particular date.
Condition here is we dont have dates below 2017, so whatever the contracts created should pick the minimum value from that particular table for that respective currency, and if there are any future contracts which is more than sysdate, then it shoudl pick latest (max rate) dates rate for that currency.
Please help me here.
create or replace
FUNCTION get_exchange_rate(
p_rate_amount IN NUMBER,
p_exchange_source IN VARCHAR2,
p_exchange_target IN VARCHAR2,
p_date IN DATE)
RETURN NUMBER
is
l_rate number := null;
BEGIN
BEGIN
SELECT exchange_rate
INTO l_rate
FROM exchange_rate_table
WHERE exchange_period='Daily'
AND exchange_target =p_exchange_target
AND exchange_source =p_exchange_source
AND begin_effect_date=p_date;
RETURN l_rate*p_rate_amount;
EXCEPTION
WHEN no_data_found THEN
SELECT exchange_rate
INTO l_rate
FROM exchange_rate_table
WHERE exchange_period='Daily'
AND exchange_target =p_exchange_target
AND exchange_source =p_exchange_source
AND begin_effect_date=
(SELECT MIN(begin_effect_date)
FROM exchange_rate_table
where 1 = 1
and exchange_source = p_exchange_source
AND exchange_target =p_exchange_target
);
RETURN l_rate*p_rate_amount;
WHEN OTHERS THEN
return null;
END;
EXCEPTION
WHEN OTHERS THEN
RETURN NULL;
END get_exchange_rate;
Sample Data:
Desired result :
Explanation :
In exchange table we have all the conversion rates from all source currencies to target currencies for all the exchange periods like Daily, Monthly,Annual.
Here in my scenario, All the source currencies should convert to target currencies as USD for that respective dates(daily rates) . like matching dates, with matching source currency codes.
When we dont have currency rates for particular local currency to USD :
Here in this case, exchange dim table has started from 01-10-2021, where contracted started on 01-09-2021, then it should pick minimum date from exchange table, (lets say in case of EUR currency.) And at the same time, we may have contracts which starts from future dates also, in that case we should pick maximum date currency rate. (eg CAD currency)
My code in snowflake:
[![enter image description here][3]][3]