Create Function To Find Candle Index Based Off Datetime (on higher tf)

Hi guys, 

I need a function that returns the index of the candle when passed a datetime value.

Similar to iBarShift(), but I need this function to handle different time frames.

Example.

I pass the datetime of a daily candle, I need it to return the weekly candle's index in which the daily candle is contained within.

Same with say a 1 hour candle timestamp, this function should be able to return the index of the relevant 4 hour candle and so on.

So the function will accept a datetime, and a timeframe to search on.

function(datetime timeStamp, int timeFrameToSearch)

Thanks