+// Check to see if two events overlap.
+//
+// This function is used in Citadel Server and in both generations of WebCit. Symlink it accordingly.
+//
+// Copyright (c) 1987-2024 by the citadel.org team
+//
+// This program is open source software. Use, duplication, or disclosure is subject to the GNU General Public License version 3.
+
+#include <libical/ical.h>
+#include <string.h>
+
+// Check to see if two events overlap. Returns nonzero if they do.
+int ical_ctdl_is_overlap(
+ struct icaltimetype t1start,
+ struct icaltimetype t1end,
+ struct icaltimetype t2start,
+ struct icaltimetype t2end
+) {
+ if (icaltime_is_null_time(t1start)) return(0);
+ if (icaltime_is_null_time(t2start)) return(0);
+
+ // if either event lacks end time, assume end = start
+ if (icaltime_is_null_time(t1end)) {
+ memcpy(&t1end, &t1start, sizeof(struct icaltimetype));
+ }
+ else {
+ if (t1end.is_date && icaltime_compare(t1start, t1end)) {
+
+ // The end date is non-inclusive so adjust it by one
+ // day because our test is inclusive, note that a day is
+ // not too much because we are talking about all day events.
+ //
+ // If start = end we assume that nevertheless the whole day is meant.
+
+ icaltime_adjust(&t1end, -1, 0, 0, 0);
+ }
+ }
+
+ if (icaltime_is_null_time(t2end)) {
+ memcpy(&t2end, &t2start, sizeof(struct icaltimetype));
+ }
+ else {
+ if (t2end.is_date && icaltime_compare(t2start, t2end)) {
+ icaltime_adjust(&t2end, -1, 0, 0, 0);
+ }
+ }
+
+ // First, check for all-day events
+ if (t1start.is_date || t2start.is_date) {
+ // If event 1 ends before event 2 starts, there is no match.
+ if (icaltime_compare_date_only(t1end, t2start) < 0) return(0);
+
+ // If event 2 ends before event 1 starts, there is no match.
+ if (icaltime_compare_date_only(t2end, t1start) < 0) return(0);
+
+ // Otherwise there is at least one day of overlap, so yes we have a match.
+ return(1);
+ }
+
+#ifdef DEBUG_ICAL_OVERLAP
+ syslog(LOG_DEBUG, "Comparing t1start %d:%d t1end %d:%d t2start %d:%d t2end %d:%d",
+ t1start.hour, t1start.minute, t1end.hour, t1end.minute,
+ t2start.hour, t2start.minute, t2end.hour, t2end.minute
+ );
+#endif
+
+ // Now check for overlaps using date *and* time.
+
+ // If event 1 ends before event 2 starts, there is no match.
+ if (icaltime_compare(t1end, t2start) <= 0) return(0);
+ // syslog(LOG_DEBUG, "calendar: first passed");
+
+ // If event 2 ends before event 1 starts, there is no match.
+ if (icaltime_compare(t2end, t1start) <= 0) return(0);
+ // syslog(LOG_DEBUG, "calendar: second passed");
+
+ // Otherwise, there is an overlap, so yes we have a match.
+ return(1);
+}