[evolution-data-server] Change how next occurrence of a recurring task is found

[Milan Crha <mcrha src gnome org>]

commit d1a6621c48612a8dcf1de8672e749b08645c07fe
Author: Milan Crha <mcrha redhat com>
Date:   Wed Mar 21 11:53:38 2018 +0100

    Change how next occurrence of a recurring task is found
    
    The previous naive "set some faraway end time" approach was also
    a performance hit for often-happen tasks, because e-cal-recur
    computes all occurrences in the given time interval first and only
    then lets the caller know with the callback, thus, with a long time
    interval most of the found occurrences had been useless. The new
    approach is adaptable and avoids this performance issue as well.

 src/calendar/libecal/e-cal-util.c |   50 +++++++++++++++++++++++++++++-------
 1 files changed, 40 insertions(+), 10 deletions(-)
---
diff --git a/src/calendar/libecal/e-cal-util.c b/src/calendar/libecal/e-cal-util.c
index c80ace3..c3fc3a8 100644
--- a/src/calendar/libecal/e-cal-util.c
+++ b/src/calendar/libecal/e-cal-util.c
@@ -1909,6 +1909,7 @@ typedef struct _NextOccurrenceData {
        struct icaltimetype interval_start;
        struct icaltimetype next;
        gboolean found_next;
+       gboolean any_hit;
 } NextOccurrenceData;
 
 static gboolean
@@ -1923,6 +1924,8 @@ ecu_find_next_occurrence_cb (icalcomponent *comp,
 
        g_return_val_if_fail (nod != NULL, FALSE);
 
+       nod->any_hit = TRUE;
+
        if (icaltime_compare (nod->interval_start, instance_start) < 0) {
                nod->next = instance_start;
                nod->found_next = TRUE;
@@ -1943,7 +1946,10 @@ e_cal_util_find_next_occurrence (icalcomponent *vtodo,
 {
        NextOccurrenceData nod;
        struct icaltimetype interval_start = for_time, interval_end, orig_dtstart, orig_due;
+       gint advance_days = 8;
+       icalproperty *prop;
        gboolean success;
+       GError *local_error = NULL;
 
        g_return_val_if_fail (vtodo != NULL, FALSE);
        g_return_val_if_fail (out_time != NULL, FALSE);
@@ -1962,22 +1968,46 @@ e_cal_util_find_next_occurrence (icalcomponent *vtodo,
        if (icaltime_is_null_time (interval_start) || !icaltime_is_valid_time (interval_start))
                interval_start = icaltime_current_time_with_zone (e_cal_client_get_default_timezone 
(cal_client));
 
-       /* Some far-enough time to cover long recurrences */
-       interval_end = icaltime_from_string ("30000101T000000Z");
+       prop = icalcomponent_get_first_property (vtodo, ICAL_RRULE_PROPERTY);
+       if (prop) {
+               struct icalrecurrencetype rrule;
+
+               rrule = icalproperty_get_rrule (prop);
+
+               if (rrule.freq == ICAL_WEEKLY_RECURRENCE && rrule.interval > 1)
+                       advance_days = (rrule.interval * 7) + 1;
+               else if (rrule.freq == ICAL_MONTHLY_RECURRENCE)
+                       advance_days = (rrule.interval >= 1 ? rrule.interval * 31 : 31) + 1;
+               else if (rrule.freq == ICAL_YEARLY_RECURRENCE)
+                       advance_days = (rrule.interval >= 1 ? rrule.interval * 365 : 365) + 2;
+       }
+
+       do {
+               interval_end = interval_start;
+               icaltime_adjust (&interval_end, advance_days, 0, 0, 0);
+
+               nod.interval_start = interval_start;
+               nod.next = icaltime_null_time ();
+               nod.found_next = FALSE;
+               nod.any_hit = FALSE;
 
-       nod.interval_start = interval_start;
-       nod.next = icaltime_null_time ();
-       nod.found_next = FALSE;
+               success = e_cal_recur_generate_instances_sync (vtodo, interval_start, interval_end,
+                       ecu_find_next_occurrence_cb, &nod,
+                       e_cal_client_resolve_tzid_sync, cal_client,
+                       e_cal_client_get_default_timezone (cal_client),
+                       cancellable, &local_error) || nod.found_next;
 
-       success = e_cal_recur_generate_instances_sync (vtodo, interval_start, interval_end,
-               ecu_find_next_occurrence_cb, &nod,
-               e_cal_client_resolve_tzid_sync, cal_client,
-               e_cal_client_get_default_timezone (cal_client),
-               cancellable, error) || nod.found_next;
+               interval_start = interval_end;
+               icaltime_adjust (&interval_start, -1, 0, 0, 0);
+
+       } while (!local_error && !g_cancellable_is_cancelled (cancellable) && !nod.found_next && nod.any_hit);
 
        if (success)
                *out_time = nod.next;
 
+       if (local_error)
+               g_propagate_error (error, local_error);
+
        if (!icaltime_is_null_time (for_time) && icaltime_is_valid_time (for_time)) {
                if (icaltime_is_null_time (orig_dtstart) || !icaltime_is_valid_time (orig_dtstart))
                        e_cal_util_remove_property_by_kind (vtodo, ICAL_DTSTART_PROPERTY, FALSE);