How to have your files always tidy: no trailing spaces, no tabs and properly indented on emacs

gistfile1.el

;;; Clean up the current buffer: indent it, remove tabs and delete the
;;; trailing whitespace.
(defun tidy-up-buffer ()
  " Do a cleanup of the current buffer: tabs, spaces and indent
it."
  (interactive)
  (indent-buffer)
  (delete-trailing-whitespace)
  (untabify-buffer))


;;; Do a general buffer cleanup before save. Markdown and text modes don't dig "blind" automatic indentation.
(add-hook 'before-save-hook #'(lambda() (unless (member major-mode '(fundamental-mode debian-changelog-mode debian-control-mode markdown-mode text-mode)) (tidy-up-buffer))))

If you want to enable on a local buffer basis do:

(add-hook 'php-mode-hook #'(lambda() (set (make-local-var'before-save-hook) #'tidy-up-buffer)))

Replace php-mode-hook with whichever mode you want this to tidying up to be active.