;;; git-email.el --- Work with git and email -*- lexical-binding: t; -*-

;; Copyright (C) 2021 yoctocell

;; Author: yoctocell <public@yoctocell.xyz>
;; URL: https://git.sr.ht/~yoctocell/git-email
;; Version: 0.1.0
;; Package-Requires: ((emacs "25.1"))
;; Keywords: git email
;; License: GNU General Public License >= 3

;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This package integrates with git and email and offers two main functions
;; - `git-email-send-email' and `git-email-apply-patch'.
;;
;; `git-email-send-email' sends an email based on a patch file generated by
;; 'git format-patch'.  It inserts the relevant headers and the diff into the
;; message buffer.
;;
;; `git-email-apply-patch' will apply the patch that you are currently viewing
;; and it will ask to for the project that the patch belongs to.

;;; TODO:

;; * Add proper syntax highlighting to diffs in the message buffer.

;;; Code:

(defgroup git-email nil
  "Work with git and email."
  :group 'convenience)

(defcustom git-email--compose-message-function 'message-mail
  "The function used to compose patch mail."
  :group 'git-email
  :type 'symbol)

(defun git-email--extract-header (header patch-file)
  "Extract HEADER from PATCH-FILE.
If the header is not found, return an empty string."
  (with-temp-buffer
    (insert-file-contents patch-file)
    (goto-char (point-min))
    (buffer-substring-no-properties
     (if (re-search-forward (format " *%s: +" header) nil t)
	 (point)
       (point-at-eol))
     (point-at-eol))))

(defun git-email--extract-diff (patch-file)
  "Extract the diff from PATCH-FILE."
  (with-temp-buffer
    (insert-file-contents patch-file)
    (goto-char (point-min))
    (buffer-substring-no-properties
     (- (re-search-forward "\n\n") 1)
     (point-max))))

(defun git-email-send-email (patch-file)
  "Given a PATCH-FILE, send an email.
Extracts the relevant headers and the diff from the PATCH-FILE and inserts
them into the message buffer."
  (interactive)
  (let* ((default-directory (cdr (project-current)))
	 (subject (git-email--extract-header "subject" patch-file))
	 (from (git-email--extract-header "from" patch-file))
	 (sendemail-to
	  (shell-command-to-string "git config --list | grep sendemail.to"))
	 (to (if (string-equal sendemail-to "")
		 "to"
	       (substring sendemail-to 13 -1))) ; Remove newline
	 (in-reply-to (git-email--extract-header "in-reply-to" patch-file))
	 (msg-id (git-email--extract-header "message-id" patch-file))
	 (diff (git-email--extract-diff patch-file)))
    (funcall git-email--compose-message-function to subject
	     `(("in-reply-to" ,in-reply-to)
	       ("message-id" ,msg-id)
	       ("from" ,from)))
    ;; (let ((body (or (re-search-forward "<#part .*>")
    ;; 		   (re-search-forward "--text follows this line--"))))
    (goto-char (point-max))
    (insert diff)))


(provide 'git-email)
;;; git-email.el ends here