Is there a sane way to extend this out to check if a directory exists, and if not then download and unzip a file to create that directory?

The problem I always have with make and bash is that, for example, I only ever want two possible states-- the successfully unzipped directory or no state at all. And the more steps I add the more little state boogers my build system acquires (e.g., partial download, dangling zip file, etc.)