Show tag statistics using rules

I want to do the following using Rules.

When new or existing content item is saved and has "positive" or "negative" tag selected and a specific taxonomy vocabulary term selected

Count the total number of content items for the selected vocabulary term with a "positive" or "negative tag"

divided by

total number of entity content items for the selected entity vocabulary term with a "positive" tag

show total as percentage

Put value in read-only custom field of the selected entity vocabulary term selected for this content item.

Is this doable using Rules? A I on the wrong track? Are you confused -- I am confused ;).

Any pointers are greatly appreciated