Introduce first draft to compute time spent on work today

This is supposed to be used later on in workload overview reports, to
make the display of the current day account for already spent time.

site-lisp/db-org.el

@@ -847,6 +847,33 @@ PARAMS is a property list of the following parameters:
 (org-dynamic-block-define "db/org-workload-overview-report"
                           #'db/org-insert-workload-overview-report)
 
+(defun db/spent-work-hours-today (&optional match)
+  "Return the time spent today on work.
+
+Relevant clock times are taken from the file in
+`org-agenda-files'.  The result returned is given as integer in
+minutes.
+
+MATCH is a Org properties match that determines what constitutes
+as work item.  When not given, defaults to all tasks except those
+given by `org-home-task-id' and `org-break-task-id'."
+  (unless match
+    (when (and (stringp org-home-task-id)
+               (not (zerop (length org-home-task-id))))
+      (setq match (concat match (format "-ID=%s" org-home-task-id))))
+    (when (and (stringp org-break-task-id)
+               (not (zerop (length org-break-task-id))))
+      (setq match (concat match (format "-ID=%s" org-break-task-id)))))
+  (->> org-agenda-files
+       (-map #'(lambda (file)           ; taken from `org-dblock-write:clocktable'
+                 (with-current-buffer (find-buffer-visiting file)
+                   (save-excursion
+                     (save-restriction
+                       (org-clock-get-table-data file (list :match match
+                                                            :block 'today)))))))
+       (-map #'cl-second)
+       -sum))
+
 
 ;;; Fixes