;;; moggle.el --- iterate headers and body in message-mode -*- lexical-binding: t -*-
;;
;; Author: Emanuel Berg <incal@dataswamp.org>
;; Created: 2014-07-04
;; Keywords: news, mail
;; License: GPL3+
;; URL: https://dataswamp.org/~incal/emacs-init/gnus/moggle.el
;; Version: 2.2.4
;;
;;; Commentary:
;;
;; In the current message, hit one (1) key to go to the next
;; field to type. The first fields in a message are the
;; headers -- "To", "Subject", and so on -- and the last one
;; is the body.
;;
;; And, there is another key to do the exact same thing, only
;; in the opposite direction!
;;
;; By default, `next-header' is bound to TAB ("\t"), and
;; `previous-header' to BACKTAB (<backtab>; i.e., right-shift
;; and TAB).
;;
;; This also plays seamlessly with the abbrevs of the
;; ~/.mailrc file. Try it: setup an alias, type it in the
;; "To" header, and hit TAB.
;;
;; For example, for mail addresses, ~/.mailrc can look like
;; this:
;;
;; alias john "John DiFool <difool@incal.com>"
;; alias kate "Katherine Moss <enquiries@katemossagency.com>"
;; alias friends john kate
;;
;; (For Usenet/Gmane groups, ordinary abbrevs are setup: geh
;; -> gnu.emacs.help (gmane.emacs.help) and so on.)
;;
;; All in all, this makes for rapid, mouse-free editing of
;; mails and Usenet/Gmane posts.
;;
;;; Code:

(require 'message)

(defun get-header-separator-pos ()
  "Get the position of `mail-header-separator'."
  (save-excursion
    (rfc822-goto-eoh)
    (point) ))

(defun at-end-of-line-p ()
  "True iff point is at the end of the current line."
  (looking-at "$"))

(defun next-line-header-or-body ()
  "Go to the next header field.
If already at the last header field go to the message body."
  (if (re-search-forward ": " (get-header-separator-pos) t)
      (end-of-line)
    (message-goto-body) ))

(defun end-of-line-or-next-line ()
  "If not at the end of a line go there.
Else got to the next header field if it exists."
  (if (at-end-of-line-p)
      (next-line-header-or-body)
    (end-of-line) ))

(defun next-header ()
  "Go to the next header field.
If already at the last one go to the message body."
  (interactive)
  (if (< (point) (get-header-separator-pos))
      (progn
        (expand-abbrev)
        (end-of-line-or-next-line) )
    (goto-char (point-min))
    (end-of-line-or-next-line) ))

(defun prev-header ()
  "Go to the previous header field.
If already at the first one got to the message body."
  (interactive)
  (if (< (point) (get-header-separator-pos))
      (progn
        (expand-abbrev)
        (if (= 1 (line-number-at-pos))
            (message-goto-body)
          (forward-line -1) )
        (end-of-line) )
    (goto-char (get-header-separator-pos))
    (backward-char 1) ))

(define-key message-mode-map "\t"      #'next-header)
(define-key message-mode-map [backtab] #'prev-header)

(provide 'moggle)
;;; moggle.el ends here