;;; db-mail.el --- Utility Functions for sending mail -*- lexical-binding: t -*-

;;; Commentary:

;;; Code:

(require 'cl-lib)
(require 'cl-macs)
(require 'mail-extr)
(require 'epg)
(require 'mml-sec)

(defun db/public-key (address &optional method)
  "Return valid public keys for ADDRESS and given METHOD.

METHOD can be \"smime\" or \"pgpmime\"; defaults to \"pgpmime\".
ADDRESS is a string containing exactly one email address."
  (check-type address string)
  (unless method (setq method "pgpmime"))
  (epg-list-keys (epg-make-context
                  (cond
                    ((string= method "smime")
                     'CMS)
                    ((string= method "pgpmime")
                     'OpenPGP)
                    (t (error "Unknown method %s" method))))
                 address))

(defun db/encryption-possible-p (recipients method)
  "Check whether sending encrypted emails to all RECIPIENTS is possible.

METHOD specifies the encrypt method used.  Can be either
\"smime\" or \"pgpmime\"."
  (cl-every (lambda (recipient)
              (not (null (db/public-key recipient method))))
            recipients))

(defun db/message-recipients ()
  "Return all recipients of the email in the current buffer."
  (cl-mapcan (lambda (field)
               (let ((field-value (message-field-value field)))
                 (when field-value
                   (mapcar #'cadr
                           (mail-extract-address-components field-value t)))))
             (list "to" "cc" "bcc")))

(defun db/signencrypt-message-when-possible ()
  "Add mml markers for signing and encryption of an email if possible."
  (interactive)
  (when (eq major-mode 'message-mode)
    (let ((from (message-field-value "from")))
      (when from
        (let ((methods (if (string-match "@tu-dresden\.de>" from)
                           (list "smime" "pgpmime")
                         (list "pgpmime")))
              (recipients (db/message-recipients)))

          ;; if there is no recipient, encrypt with default method
          (if (null recipients)
              (mml-secure-message (cl-first methods) 'signencrypt)

            ;; go through available keys
            (let ((available-method
                   (cl-find-if (lambda (method)
                                 (db/encryption-possible-p recipients method))
                               methods)))

              (if available-method
                  (mml-secure-message available-method 'signencrypt)

                ;; if nothing works, sign with default method
                (mml-secure-message (cl-first methods) 'sign)))))))))

(defun db/gnus-save-newsrc-with-whitespace-1 ()
  "Save ~/.newsrc.eld with extra whitespace."
  ;; http://ding.gnus.narkive.com/pq3Z8ZjQ/pretty-printing-newsrc-eld#post3
  (gnus-message 5 "Adding whitespace to .newsrc.eld")
  (save-excursion
    (goto-char (point-min))
    (while (re-search-forward "(\\\"\\| ((\\| (nn" nil t)
      (replace-match "\n \\&" t))
    (delete-trailing-whitespace)))

(defun db/gnus-summary-open-Link ()
  "Open link named \"Link\" in current article."
  (interactive)
  (save-window-excursion
   (save-mark-and-excursion
    (save-restriction
     (widen)
     (let ((url nil))
       (unless (eq major-mode 'gnus-article-mode)
         (gnus-summary-select-article-buffer))
       (goto-char (point-min))
       (while (and (not url)
                   (search-forward "Link"))
         (backward-char)
         (setq url (get-text-property (point) 'shr-url)))
       (when url
         (browse-url url)))))))

(defun db/gnus-html-mime-part-to-org ()
  "Convert current gnus article to org mode."
  (interactive)
  (let ((return-code (gnus-mime-pipe-part "pandoc -f html -t org")))
    (unless (zerop return-code)
      (error "Error in extracting text"))
    (with-current-buffer "*Shell Command Output*"
      (kill-ring-save (point-min) (point-max)))))

(defun db/set-smtp-server-from-header (orig-fun &rest args)
  "Choose smtp-settings dynamically, based on the From: header
entry of the current mail."
  (require 'mail-extr)
  (let* ((from    (or (save-restriction
                        (message-narrow-to-headers)
                        (mail-fetch-field "From"))
                      user-mail-address))
         (address (cadr (mail-extract-address-components from)))
         (account (assoc address db/mail-accounts)))
    (message "Using address: %s" address)
    (if account
        (progn
          (message "Sending with account for %s" address)
          ;; XXX: these calls to `nth’ should be abstracted away
          (let ((smtpmail-smtp-server (nth 3 account))
                (smtpmail-stream-type (nth 4 account))
                (smtpmail-smtp-service (nth 5 account))
                (smtpmail-smtp-user (nth 6 account)))
            (apply orig-fun args)))
      (progn
        (message "Sending with default account settings")
        (apply orig-fun args)))))

(provide 'db-mail)
;;; db-mail ends here