I am currently looking at creating a new type of site archive within WordPress that allows users to filter by category AND by year rather than the default category OR year.

I am hoping to build a sidebar widget that creates the interface but I am looking for ideas and advice on creating the custom permalink setup. Ideally the archive will work with URLs along the lines of:

/category/year/

/category-1/year/

etc.

I have no requirement to filter any deeper than year. I have discovered this snippet of code but it does not work as expected.

Thanks