Open a .sketch file

Sketch is a digital design tool for mac. When you save a file it saves it as .sketch This file is type application/zip so it contains files. What I need is to access the JSON files that it has (path pages/[login to view URL]). Step of what the app will do : 1. have a button which will open a file manager where you can search for the .sketch file 2. access the json file inside the .sketch file (directory pages/[login to view URL]) 3. create NSJSONSerialization object from the json file 4. Write back the NSJSONSerialization to the json file 5. make sure the .sketch file is working Should use objective-c and only native libralies(app kit).