I am trying to find out how to calculate the highest high and lowest low values for an indicator over a period in MQL4.

For example:

Using amibroker (similar sor metastock) the formula would be as below to calculate the highest high of the 30 day moving average over the last 10 periods.

Highest high = HHV(MA(Close,30),10 )
I have tried using ArrayMaximum() but this returns the position and not the value of the highest value.
Also Highest() does not work with indicators.

Any help will be much appreciated