Is there something as Re-Indent (in Xcode) or Smart Indent (in Matlab) for TeXShop?
Unfortunately there is no way to do this in TeXShop. It's probably the one major failing of it as an editor. You can select portions of text and indent them but since TeXShop soft-wraps lines, this doesn't always do what you want it to do. The code is open-source, and new additions are always welcome, though.