[PATCH 3/4] emacs: possibility to customize the rendering of tags

[Damien Cassou]

This patch extracts the rendering of tags in notmuch-show to a
dedicated notmuch-tagger file.

This new file introduces a `notmuch-tagger-formats' variable that
associates each tag to a particular format. For example,

(("unread"
  (:propertize "unread" face
               (:foreground "red")))
 ("flagged"
  (:propertize "flagged" display
               (image :type svg :file "~/notmuch/emacs/resources/star.svg" :ascent center :mask heuristic))))

associates a red font to the "unread" tag and a star picture to
the "flagged" tag.

In the future, I would like to use the Customization interface of
Emacs to edit this variable and also to provide high-lever
functions to manipulate it such
that (notmuch-tagger-propertize "unread" :foreground "red")
and (notmuch-tagger-picture "flagged" "star.svg").

`mode-line-format' templates are used to represent the format for
each tag. This is a concize format that can also be used in
`header-line-format' if later desired.

Signed-off-by: Damien Cassou <damien.cassou at gmail.com>
---
 emacs/notmuch-show.el   |    7 ++---
 emacs/notmuch-tagger.el |   75 +++++++++++++++++++++++++++++++++++++++++++++++
 emacs/notmuch.el        |    5 ++--
 3 files changed, 80 insertions(+), 7 deletions(-)
 create mode 100644 emacs/notmuch-tagger.el

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 1864dd1..7bf9f3c 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -36,6 +36,7 @@
 (require 'notmuch-mua)
 (require 'notmuch-crypto)
 (require 'notmuch-print)
+(require 'notmuch-tagger)
 
 (declare-function notmuch-call-notmuch-process "notmuch" (&rest args))
 (declare-function notmuch-fontify-headers "notmuch" nil)
@@ -362,8 +363,7 @@ operation on the contents of the current buffer."
     (if (re-search-forward "(\\([^()]*\\))$" (line-end-position) t)
 	(let ((inhibit-read-only t))
 	  (replace-match (concat "("
-				 (propertize (mapconcat 'identity tags " ")
-					     'face 'notmuch-tag-face)
+				 (notmuch-tagger-present-tags tags)
 				 ")"))))))
 
 (defun notmuch-clean-address (address)
@@ -441,8 +441,7 @@ message at DEPTH in the current thread."
 	    " ("
 	    date
 	    ") ("
-	    (propertize (mapconcat 'identity tags " ")
-			'face 'notmuch-tag-face)
+	    (notmuch-tagger-present-tags tags)
 	    ")\n")
     (overlay-put (make-overlay start (point)) 'face 'notmuch-message-summary-face)))
 
diff --git a/emacs/notmuch-tagger.el b/emacs/notmuch-tagger.el
new file mode 100644
index 0000000..90730f6
--- /dev/null
+++ b/emacs/notmuch-tagger.el
@@ -0,0 +1,75 @@
+;; notmuch-tagger.el --- Library to improve the way tags are displayed
+;;
+;; Copyright © Damien Cassou
+;;
+;; This file is part of Notmuch.
+;;
+;; Notmuch 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.
+;;
+;; Notmuch 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 Notmuch.  If not, see <http://www.gnu.org/licenses/>.
+;;
+;; Authors: Damien Cassou <damien.cassou at gmail.com>
+;;; Commentary:
+;;
+;;; Comments
+;;
+;;; Code:
+;;
+
+(require 'cl)
+
+(defvar notmuch-tagger-formats
+  `(("unread"
+     (:propertize "unread" face
+                  (:foreground "red")))
+    ("flagged"
+     (:propertize "flagged" display
+                  (image :type svg :file
+                         ,(expand-file-name
+                           "resources/star.svg"
+                           (file-name-directory
+                            (or
+                             (locate-library "notmuch-tagger")
+                             (buffer-file-name))))
+                         :ascent center :mask heuristic))))
+  "Contains pairs of (KEY FORMAT) to format a tag matching KEY.
+
+KEY must be a string with a tag name. In the future, KEY could
+also be a regexp or list of keys to be matched against tags.
+
+The default value set the unread tag to be red and the flagged
+tag to have a star picture attached. Those are just examples so
+you get an idea of what you can do.")
+
+(defun notmuch-tagger-tag-format (tag)
+  "Format TAG as a `mode-line-format' template.
+
+The format to apply to TAG is searched in
+`notmuch-tagger-formats'. If not found, the default
+`notmuch-tag-face' is used."
+  (let ((match (assoc tag notmuch-tagger-formats)))
+    (if match
+        (cadr match)
+      `(:propertize ,tag face notmuch-tag-face))))
+
+(defun notmuch-tagger-tags-format (tags)
+  "Format TAGS as a `mode-line-format' template."
+  (notmuch-intersperse
+   (remove nil (mapcar #'notmuch-tagger-tag-format tags))
+   " "))
+
+(defun notmuch-tagger-present-tags (tags)
+  "Return a string that represent TAGS with their format."
+  (format-mode-line (notmuch-tagger-tags-format tags)))
+
+(provide 'notmuch-tagger)
+;;; notmuch-tagger.el ends here
diff --git a/emacs/notmuch.el b/emacs/notmuch.el
index c98a4fe..c607905 100644
--- a/emacs/notmuch.el
+++ b/emacs/notmuch.el
@@ -797,9 +797,8 @@ non-authors is found, assume that all of the authors match."
     (notmuch-search-insert-authors format-string (plist-get result :authors)))
 
    ((string-equal field "tags")
-    (let ((tags-str (mapconcat 'identity (plist-get result :tags) " ")))
-      (insert (propertize (format format-string tags-str)
-			  'face 'notmuch-tag-face))))))
+    (let ((tags (plist-get result :tags)))
+      (insert (format format-string (notmuch-tagger-present-tags tags)))))))
 
 (defun notmuch-search-show-result (result &optional pos)
   "Insert RESULT at POS or the end of the buffer if POS is null."
-- 
1.7.10.4