changing legends on pie chart

HI

i have two columns connected each other

for example 

category-> product

for each product a sum sales.

i have slicer with the categories.

i have a pie chart and i want it to act like this:

when no category selected, to show the legend -"all" and the value will be the whole sales

when categroy is selected, to show the category's products legend/

now, when no category is selected the pie shows billion of products legends

do you have an idea? hope i was clear

thanks!