config/cron/job.guile: Don't sync emails when key is not cached.

This avoid unexpected lost of focus in Emacs.

.config/cron/job.guile

@@ -1,8 +1,36 @@
 ;; -*- mode: scheme; -*-
+(use-modules (ice-9 popen))
+(use-modules (rnrs io ports))
 
 ;; This cannot be let-bound within `job'.
 (define currency-file (string-append (getenv "HOME") "/.cache/currency.units"))
 
+(define* (system-to-string #:rest args)
+  (let* ((port (apply open-pipe* OPEN_READ args))
+         (str (get-string-all port)))
+    (close-pipe port)
+    str))
+
+(define (gpg-keyinfo)
+  "Return GPG keyinfo as a list of list of strings.
+Typical output is:
+
+S KEYINFO ???????????????????????????????????????? D - - - P - - -
+S KEYINFO ???????????????????????????????????????? D - - 1 P - - -
+
+The \"1\" means the key is cached."
+  (filter (lambda (info) (string= (car info) "S"))
+          (map (lambda (s) (string-split s #\space))
+               (string-split
+                (system-to-string "gpg-connect-agent" "keyinfo --list" "/bye")
+                #\newline))))
+
+(define (gpg-key-cached?)
+  "Return #t of a key is cached in the GPG agent, #f otherwise."
+  (let ((keyinfo (gpg-keyinfo)))
+    (not (null? (filter (lambda (info) (string= (list-ref info 6) "1"))
+                        keyinfo)))))
+
 (job
  (lambda (current-time)
    (let* ((seconds-in-a-day (* 60 60 24))
@@ -21,5 +49,8 @@
 (job '(next-hour (range 0 24 3)) "updatedb-local")
 
 (job '(next-minute (range 0 60 15))
-     '(system* "notmuch" "new")         ; Email is sync'ed from a pre-new hook.
+     (lambda ()
+       (when (gpg-key-cached?)
+         ;; Email is sync'ed from a pre-new hook.
+         (system* "notmuch" "new")))
      "mail")