Open vim, type code. Done. Hold `u` for playing backwards, or `Ctrl-r` for playing forwards. If you want to show your undos too, then remap `g-` and `g+` to something you can hold and use those instead. If you want to save that undo history, set options `undofile` and `undodir` and perhaps `undolevels` if 1000 is too little.