;;; piem-gnus.el --- Gnus integration for piem  -*- lexical-binding: t; -*-

;; Copyright (C) 2020-2021  Kyle Meyer

;; Author: Kyle Meyer <kyle@kyleam.com>
;; Keywords: vc, tools
;; Package-Requires: ((emacs "26.3"))

;; 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 library provides a minor mode, `piem-gnus-mode', that modifies
;; `piem' variables to teach functions like `piem-inbox' and
;; `piem-am-ready-mbox' how to extract information from Gnus buffers.

;;; Code:

(require 'gnus)
(require 'gnus-sum)
(require 'message)
(require 'piem)
(require 'rfc2047)

(defgroup piem-gnus nil
  "Gnus integration for piem."
  :group 'piem)

(defun piem-gnus-get-inbox ()
  "Return inbox name from a Gnus article"
  (when (derived-mode-p 'gnus-article-mode 'gnus-summary-mode)
    (with-current-buffer gnus-original-article-buffer
      (piem-inbox-by-header-match))))

(defun piem-gnus-get-mid ()
  "Return the message ID of a Gnus article."
  (when (derived-mode-p 'gnus-article-mode 'gnus-summary-mode)
    (with-current-buffer gnus-original-article-buffer
      (when-let ((mid (message-field-value "Message-ID")))
        (if (string-match (rx string-start (zero-or-more space) "<"
                              (group (one-or-more (not (any ">"))))
                              ">" (zero-or-more space) string-end)
                          mid)
            (match-string 1 mid)
          mid)))))

;; If there is an easy way to generate an mbox for a thread in Gnus, a
;; function for `piem-mid-to-thread-functions' should be defined.

(defun piem-gnus-am-ready-mbox ()
  "Return a function that inserts an am-ready mbox.
If the buffer has any MIME parts that look like a patch, use
those parts' contents (in order) as the mbox.  Otherwise, use the
message itself if it looks like a patch."
  (when (derived-mode-p 'gnus-article-mode 'gnus-summary-mode)
    (cond
     (gnus-article-mime-handles
      (when-let ((patches
                  (delq nil
                        (mapcar (lambda (handle)
                                  (and (listp handle)
                                       (piem-am-patch-attachment-p
                                        (mm-handle-media-type handle)
                                        (mm-handle-filename handle))
                                       (with-temp-buffer
                                         (mm-display-inline handle)
                                         (buffer-substring-no-properties
                                          (point-min) (point-max)))))
                                gnus-article-mime-handles))))
        (cons (lambda ()
                (dolist (patch patches)
                  (insert patch)))
              "mbox")))
     (gnus-article-buffer
      (when-let ((patch (with-current-buffer gnus-article-buffer
                          (save-restriction
                            (widen)
                            (and (string-match-p
                                  piem-patch-subject-re
                                  (rfc2047-decode-string
                                   (message-field-value "subject")))
                                 (buffer-substring-no-properties
                                  (point-min) (point-max)))))))
        (cons (lambda () (insert patch))
              "mbox"))))))

;;;###autoload
(define-minor-mode piem-gnus-mode
  "Toggle Gnus support for piem.
With a prefix argument ARG, enable piem-gnus mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil."
  :global t
  :init-value nil
  (if piem-gnus-mode
      (progn
        (add-hook 'piem-am-ready-mbox-functions #'piem-gnus-am-ready-mbox)
        (add-hook 'piem-get-inbox-functions #'piem-gnus-get-inbox)
        (add-hook 'piem-get-mid-functions #'piem-gnus-get-mid))
    (remove-hook 'piem-am-ready-mbox-functions #'piem-gnus-am-ready-mbox)
    (remove-hook 'piem-get-inbox-functions #'piem-gnus-get-inbox)
    (remove-hook 'piem-get-mid-functions #'piem-gnus-get-mid)))

;;; piem-gnus.el ends here
(provide 'piem-gnus)