;;; eudcb-mailabbrev.el --- EUDC - mailabbrev backend -*- lexical-binding: t -*-

;; Copyright (C) 2022 condition-alpha.com

;; 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 an interface to the mailabbrev package as
;;    an EUDC data source.

;;; Usage:
;;    To load the library, first `require' it:
;;
;;      (require 'eudcb-mailabbrev)
;;
;;    In the simplest case then just use:
;;
;;      (eudc-mailabbrev-set-server "localhost")
;;
;;    When using `eudc-server-hotlist', instead use:
;;
;;      (add-to-list 'eudc-server-hotlist '("localhost" . mailabbrev))

;;; Code:

(require 'eudc)
(require 'mailabbrev)
(require 'mail-parse)

;; hook ourselves into the EUDC framework
(eudc-protocol-set 'eudc-query-function
		   'eudc-mailabbrev-query-internal
		   'mailabbrev)
(eudc-protocol-set 'eudc-list-attributes-function
		   nil
		   'mailabbrev)
(eudc-protocol-set 'eudc-protocol-attributes-translation-alist
		   nil
		   'mailabbrev)
(eudc-protocol-set 'eudc-protocol-has-default-query-attributes
		   nil
		   'mailabbrev)

(defun eudc-mailabbrev-query-internal (query &optional _return-attrs)
  "Query `mailabbrev' with QUERY.
QUERY is a list of cons cells (ATTR . VALUE).  Since `mailabbrev'
does not provide attributes in the usual sense, the
back-end-specific attribute names in
`eudc-mailabbrev-attributes-translation-alist' are used as the
KEY (that is, the \"type\" of match) when looking for matches in
`mailabbrev-database'.

RETURN-ATTRS is a list of attributes to return, defaulting to
`eudc-default-return-attributes'."
  (mail-abbrevs-setup)
  (let (result)
    (dolist (term query)
      (let* ((attr (car term))
             (value (cdr term))
             (match (symbol-value (intern-soft value mail-abbrevs))))
        (when (and match
                   (memq attr '(email firstname name)))
          ;; try to decompose email construct
          (let* ((decoded (mail-header-parse-address match t))
                 (name (cdr decoded))
                 (email (car decoded)))
            (if decoded
                ;; decoding worked, push individual fields
                (push `((email . ,email)
                        ,@(when name (list (cons 'name name))))
                      result)
              ;; else, just forward the value as-is
              (push (list (cons 'email match)) result))))))
    result))

(defun eudc-mailabbrev-set-server (dummy)
  "Set the EUDC server to `mailabbrev'.
The server in DUMMY is not actually used, since this backend
always and implicitly uses the mailabbrev package in the current
Emacs instance running on the local host."
  (interactive)
  (eudc-set-server dummy 'mailabbrev)
  (message "[eudc] mailabbrev server selected"))

(eudc-register-protocol 'mailabbrev)

(provide 'eudcb-mailabbrev)

;;; eudcb-mailabbrev.el ends here