Display remaining effort of items in workload reports

This is rather experimental, but seems to work fine so far.  The most
complicated part is to compute the overall clocked time of an item.

Any clocktime modifiers like “today” or “total” are currently ignored.

site-lisp/db-org.el

@@ -394,6 +394,53 @@ should not be clocked."
   (interactive)
   (message org-clock-current-task))
 
+(defun db/org-clocked-time-for-current-item ()
+  "Return all clocked time for Org item at point.
+
+Also includes the currently running clock when the current item
+is clocked in."
+
+  (unless (derived-mode-p 'org-mode)
+    (user-error "Not in Org mode buffer, aborting"))
+
+  (let ((at-current-clock-p (and (markerp org-clock-hd-marker)
+                                 (save-mark-and-excursion ; from `org-clock-in'
+                                   (org-back-to-heading t)
+                                   (and (eq (marker-buffer org-clock-hd-marker)
+                                            (org-base-buffer (current-buffer)))
+                                        (= (point) (marker-position org-clock-hd-marker))
+                                        (equal org-clock-current-task (org-get-heading t t t t)))))))
+
+    (+ (org-clock-sum-current-item)
+       (if at-current-clock-p
+           ;; From `org-clock-get-clocked-time'
+           (floor (org-time-convert-to-integer
+                   (org-time-since org-clock-start-time))
+                  60)
+         0))))
+
+(defun db/org-remaining-effort-of-current-item ()
+  "Return remaining effort of Org item at point, as duration.
+
+The remaining effort is computed as the planned effort minus the
+already clocked time.  If this result is negative, return zero.
+
+If no effort is specified, return nil."
+
+  (if (derived-mode-p 'org-agenda-mode)
+
+      ;; XXX: is this the right way to do it?
+      (org-agenda-with-point-at-orig-entry
+       nil (db/org-remaining-effort-of-current-item))
+
+    (unless (derived-mode-p 'org-mode)
+      (user-error "Not in Org mode buffer, aborting"))
+
+    (when-let ((effort (org-entry-get (point) "Effort")))
+      (org-duration-from-minutes
+       (max 0 (- (org-duration-to-minutes effort)
+                 (db/org-clocked-time-for-current-item)))))))
+
 
 ;;; Task Management
 
@@ -406,9 +453,10 @@ scheduled, have an active timestamp, or are deadline in the given
 time range.
 
 The result has the form (TOTAL-TIME . TASKS), where TASKS is a
-list of cons cells (ID . EFFORT).  The total time is given as an
-Org mode time string of the form hh:mm, as are all EFFORT
-entries.
+list of cons cells (ID . REMAINING-EFFORT).  REMAINING-EFFORT is
+computed as per `db/org-remaining-effort-of-current-item', which
+see.  The total time is given as an Org mode time string of the
+form hh:mm, as is REMAINING-EFFORT entries.
 
 When ORG-QL-MATCH, an org-ql sexp, is given, filter the list of
 tasks in range by this expression.  When ORG-QL-MATCH is not
@@ -436,7 +484,7 @@ imposed on the respective time range."
                   :from (org-agenda-files)
                   :select '(cons
                             (org-id-get-create)
-                            (org-entry-get (point) "Effort"))
+                            (db/org-remaining-effort-of-current-item))
                   :where `(and ,(or org-ql-match '(todo))
                                ;; Is this redundant?  Could we just stick with `ts-active'?
                                (or (scheduled ,@start-date-expr ,@end-date-expr)
@@ -477,8 +525,8 @@ PARAMS is a property list of the following parameters:
   `timestamp', `scheduled', or `deadline'.
 
 All tasks between `:start-date' and `:end-date' will be collected
-and their effort summed up.  The date format is everything
-understood by `org-read-date'."
+and their remaining effort summed up.  The date format is
+everything understood by `org-read-date'."
   (let* ((start-date (plist-get params :start-date))
          (end-date (plist-get params :end-date))
          (org-ql-match (plist-get params :org-ql-match))