pdf-annot: Add function to sort the date field

Previously, the `date` field was sorted alphabetically, instead of
according to date.

Changes:
* lisp/pdf-annot.el (pdf-annot--make-entry-formatter): Propertize
string to include the lisp date.
(pdf-annot-list-mode): Add function to sort date.

Notes:
- Why use `propertize` instead of parsing the string back?
  + Because there are annotations with no associated dates. In this
  case, we display the string "No date". Our parsing code would have
  to handle that, `propertize` is just simpler and covers all edge-cases
  correctly.
- What can we do better?
  + Currently, the index of the field we are looking up is hard-coded.
  So any change in the fields will impact this code silently. We need
  to add tests to ensure this is caught.

Closes: #75

1 files changed, 24 insertions, 3 deletions

diff --git a/lisp/pdf-annot.el b/lisp/pdf-annot.el
index 86b483e..4a8c2e9 100644
--- a/lisp/pdf-annot.el
+++ b/lisp/pdf-annot.el
@@ -1642,7 +1642,9 @@ pretty-printed output."
            (lambda (str)
              (replace-regexp-in-string "\n" " " str t t))))
       (cl-ecase entry-type
-        (date (pdf-annot-print-property a 'modified))
+        (date (propertize (pdf-annot-print-property a 'modified)
+                          'date
+                          (pdf-annot-get a 'modified)))
         (page (pdf-annot-print-property a 'page))
         (label (funcall prune-newlines
                         (pdf-annot-print-property a 'label)))
@@ -1669,19 +1671,38 @@ pretty-printed output."
                  pdf-annot-list-format))))
 
 (define-derived-mode pdf-annot-list-mode tablist-mode "Annots"
+  ;; @TODO: Remove the hard-coded index values here, and figure out a
+  ;; way to properly link this to the index values of
+  ;; `pdf-annot-list-format'.
+
+  ;; @TODO: Add tests for annotation formatting and display
   (let* ((page-sorter
           (lambda (a b)
             (< (string-to-number (aref (cadr a) 0))
                (string-to-number (aref (cadr b) 0)))))
+         (date-sorter
+          (lambda (a b)
+            (time-less-p (get-text-property 0 'date (aref (cadr a) 3))
+                         (get-text-property 0 'date (aref (cadr b) 3)))))
          (format-generator
           (lambda (format)
             (let ((field (car format))
                   (width (cdr format)))
               (cl-case field
-                (page `("Pg." 3 ,page-sorter :read-only t :right-alight t))
+                (page `("Pg."
+                        ,width
+                        ,page-sorter
+                        :read-only t
+                        :right-align t))
+                (date `("Date"
+                        ,width
+                        ,date-sorter
+                        :read-only t))
                 (t (list
                     (capitalize (symbol-name field))
-                    width t :read-only t)))))))
+                    width
+                    t
+                    :read-only t)))))))
     (setq tabulated-list-entries 'pdf-annot-list-entries
           tabulated-list-format (vconcat
                                  (mapcar