Take recency into account when scoring

Also add new user option `mailaprop-show-scores' to control whether or
not to display each candidate's score next to the sent/received counts.

mailaprop.el

@@ -19,6 +19,7 @@
 
 (require 'cl-lib)
 (require 'company)
+(require 'org) ; just for `org-time-stamp-to-now'
 
 ;; The user must set this.
 (defvar mailaprop-address-file nil
@@ -147,6 +148,12 @@ would return for that candidate substring.")
   "*How much of the address to be completed must be present before
 mailaprop offers completion.  This is a positive integer.")
 
+(defvar mailaprop-show-scores nil
+  "*If non-nil, show each candidate's score (rounded to two decimal
+  places) in square braces, to the right of the candidate's
+  sent/received counts in parentheses.  This is useful if you
+  want to monitor how the scoring formula is doing.")
+
 (defvar mailaprop-drop-address-fn nil
   "*If non-nil, a user-defined function to decide whether to drop an address.
 The function returns non-nil iff the given address should be dropped.
@@ -235,12 +242,14 @@ RAW-ADDRESSES is a list as read from `mailaprop-address-file'."
                        (funcall mailaprop-drop-address-fn
                                 group-key-addr group-size addr)))
               (let* ((date (nth 1 addr-entry))
+                     (days (abs (condition-case nil
+                                    (org-time-stamp-to-now date)
+                                  (error 65536))))
                      (sent (nth 2 addr-entry))
                      (recv (nth 3 addr-entry))
-                     ;; Sending to counts twice as much as receiving from.
-                     ;; (We should use the date and incorporate
-                     ;; recency into the score too.)
-                     (score (+ (* sent 2) recv)))
+                     ;; Sending to counts twice as much as receiving from,
+                     ;; and recency counts (with square-root dropoff).
+                     (score (/ (+ (* sent 2) recv) (sqrt days))))
                 (setq lst (cons (list addr date score) lst))
                 (let ((annotation (vector date sent recv score)))
                   (puthash addr annotation mailaprop-annotations)))))
@@ -428,7 +437,8 @@ If there is no score corresponding to ADDR, return zero."
                         (mailaprop-get-candidates arg)))
     (post-completion  nil)
     (annotation       (let ((sent-count (mailaprop-find-sent-count arg))
-                            (recv-count (mailaprop-find-recv-count arg)))
+                            (recv-count (mailaprop-find-recv-count arg))
+                            (score      (mailaprop-find-score      arg)))
                         (concat 
                          ;; Should we offer customizable annotations?
                          "  |  " (mailaprop-find-date arg)
@@ -439,11 +449,9 @@ If there is no score corresponding to ADDR, return zero."
                                    ", "
                                    (number-to-string recv-count)))
                          ")"
-                         ;; We used to have another entry here, showing
-                         ;; the raw score in parentheses.  But now that
-                         ;; we show the sent count and received count,
-                         ;; the raw score is less useful, so we dropped it.
-                         )))
+                         (if mailaprop-show-scores
+                             (concat "  [" (format "%.2f" score) "]")
+                           ""))))
     (sorted           t)
     (ignore-case      t)
     (no-cache         t)