From 111e6886564abbf3becb2a94e66f235f502b79d9 Mon Sep 17 00:00:00 2001
From: Mikhail Skorzhinskii <mskorzhinskiy@eml.cc>
Date: Sat, 12 Sep 2020 18:52:39 +0200
Subject: [PATCH 3/3] ox-icalendar.el: introduce setting to force alarms

This is a new setting for icalendar exports to allow users set alarms
exactly at the event start. With this setting set to non-nil and alarm
set to zero (by global setting or APPT_WARNTIME property) it will create
an alarm at the event start.

Note, that zero alarm set as APPT_WARNTIME property will override
default warning time.
---
 etc/ORG-NEWS         | 10 ++++++++++
 lisp/ox-icalendar.el | 24 +++++++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index b912e807d..eb950d934 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -23,6 +23,16 @@ path.
 Through these new options for icalendar export, one can customise the
 looks of summary lines in exported events.
 
+*** New option ~org-icalendar-force-alarm~
+
+This is a new setting for icalendar exports to allow users set alarms
+exactly at the event start. With this setting set to non-nil and alarm
+set to zero (by global setting or APPT_WARNTIME property) it will
+create an alarm at the event start.
+
+Note, that zero alarm set as =APPT_WARNTIME= property will override
+default warning time.
+
 * Version 9.4
 ** Incompatible changes
 *** Possibly broken internal file links: please check and fix
diff --git a/lisp/ox-icalendar.el b/lisp/ox-icalendar.el
index f110a4b2b..baed925e8 100644
--- a/lisp/ox-icalendar.el
+++ b/lisp/ox-icalendar.el
@@ -64,6 +64,15 @@ for timed events.  If non-zero, alarms are created.
   :version "24.1"
   :type 'integer)
 
+(defcustom org-icalendar-force-alarm nil
+  "Non-nil means alarm will be created even if is set to zero.
+
+This overrides default behaviour where zero means no alarm. With
+this set to non-nil and alarm set to zero, alarm will be created
+and will fire at the event start."
+  :group 'org-export-icalendar
+  :type 'bool)
+
 (defcustom org-icalendar-combined-name "OrgMode"
   "Calendar name for the combined iCalendar representing all agenda files."
   :group 'org-export-icalendar
@@ -797,8 +806,11 @@ Return VALARM component as a string, or nil if it isn't allowed."
   (let ((alarm-time
 	 (let ((warntime
 		(org-element-property :APPT_WARNTIME entry)))
-	   (if warntime (string-to-number warntime) 0))))
-    (and (or (> alarm-time 0) (> org-icalendar-alarm-time 0))
+	   (if warntime (string-to-number warntime) nil))))
+    (and (or (and alarm-time
+		  (> alarm-time 0))
+	     (> org-icalendar-alarm-time 0)
+	     org-icalendar-force-alarm)
 	 (org-element-property :hour-start timestamp)
 	 (format "BEGIN:VALARM
 ACTION:DISPLAY
@@ -806,7 +818,13 @@ DESCRIPTION:%s
 TRIGGER:-P0DT0H%dM0S
 END:VALARM\n"
 		 summary
-		 (if (zerop alarm-time) org-icalendar-alarm-time alarm-time)))))
+		 (if org-icalendar-force-alarm
+		     (if alarm-time
+			 alarm-time
+		       org-icalendar-alarm-time)
+		   (if (zerop alarm-time)
+		       org-icalendar-alarm-time
+		     alarm-time))))))
 
 
 ;;;; Template
-- 
2.28.0