Contour plot for consonant random variables

I wanted to plot a Contour function which is in following form. pi(x) = { fi (x/0.5) 0 < x <= 0.5 1 0.5 <=x <= 0.79 fi((2-x)/(2 - 0.79)) 0.79

I don't know which package allows me to give input in this format where intervals are random. Please suggest how to do this. Thanking You