core/timeline: Add support for augmented timelines

Augmented timelines increase the range of dates from its subscribers
by the specified factor. They're useful for the interactive views,
since they prevent fetching new events so often as when views change.

Add the necessary API.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/755>

src/core/gcal-timeline.c

@@ -36,8 +36,11 @@ struct _GcalTimeline
 {
   GObject             parent_instance;
 
+  double              augmentation_factor;
+
   guint               update_range_idle_id;
   GcalRange          *range;
+  GcalRange          *augmented_range;
 
   GcalRangeTree      *events;
   gchar              *filter;
@@ -184,6 +187,50 @@ set_model_on_subscriber (GcalTimelineSubscriber *subscriber,
   GCAL_TIMELINE_SUBSCRIBER_GET_IFACE (subscriber)->set_model (subscriber, model);
 }
 
+static GcalRange *
+augment_range (GcalRange *range,
+               double     augmentation_factor)
+{
+  g_autoptr (GcalRange) augmented_range = NULL;
+  g_autoptr (GDateTime) range_start = NULL;
+  g_autoptr (GDateTime) range_end = NULL;
+  GTimeSpan timespan;
+  GTimeSpan offset;
+
+  g_assert (range != NULL);
+  g_assert (augmentation_factor >= 1.0 || G_APPROX_VALUE (augmentation_factor, 1.0, DBL_EPSILON));
+
+  if (G_APPROX_VALUE (augmentation_factor, 1.0, DBL_EPSILON))
+    {
+#ifdef GCAL_ENABLE_TRACE
+      GCAL_TRACE_MSG ("%s: Augmenting range by 1.0, skipping", G_STRFUNC);
+#endif
+      return gcal_range_ref (range);
+    }
+
+  range_start = gcal_range_get_start (range);
+  range_end = gcal_range_get_end (range);
+
+  timespan = g_date_time_difference (range_end, range_start);
+  g_assert (timespan > 0);
+
+  offset = (timespan / 2) * augmentation_factor;
+
+  augmented_range = gcal_range_new_take (g_date_time_add (range_start, -offset),
+                                         g_date_time_add (range_end, offset),
+                                         gcal_range_get_range_type (range));
+#ifdef GCAL_ENABLE_TRACE
+    {
+      g_autofree char *range_str = gcal_range_to_string (range);
+      g_autofree char *augmented_range_str = gcal_range_to_string (augmented_range);
+
+      GCAL_TRACE_MSG ("%s: Range %s augmented to %s", G_STRFUNC, range_str, augmented_range_str);
+    }
+#endif
+
+  return g_steal_pointer (&augmented_range);
+}
+
 static void
 update_range (GcalTimeline *self)
 {
@@ -224,15 +271,43 @@ update_range (GcalTimeline *self)
 
       if (!self->range || gcal_range_compare (self->range, new_range) != 0)
         {
+          g_autoptr (GcalRange) new_augmented_range = NULL;
+
           g_clear_pointer (&self->range, gcal_range_unref);
           self->range = g_steal_pointer (&new_range);
-          range_changed = TRUE;
+
+          if (self->augmented_range)
+            {
+              switch (gcal_range_calculate_overlap (self->range, self->augmented_range, NULL))
+                {
+                case GCAL_RANGE_NO_OVERLAP:
+                case GCAL_RANGE_INTERSECTS:
+                case GCAL_RANGE_SUPERSET:
+                  g_clear_pointer (&self->augmented_range, gcal_range_unref);
+                  self->augmented_range = augment_range (self->range, self->augmentation_factor);
+                  range_changed = TRUE;
+                  break;
+
+                case GCAL_RANGE_SUBSET:
+                case GCAL_RANGE_EQUAL:
+                  break;
+
+                default:
+                  g_assert_not_reached ();
+                }
+            }
+          else
+            {
+              self->augmented_range = augment_range (self->range, self->augmentation_factor);
+              range_changed = TRUE;
+            }
         }
 
     }
   else if (self->range)
     {
       g_clear_pointer (&self->range, gcal_range_unref);
+      g_clear_pointer (&self->augmented_range, gcal_range_unref);
       range_changed = TRUE;
     }
 
@@ -242,7 +317,7 @@ update_range (GcalTimeline *self)
 
       g_hash_table_iter_init (&iter, self->calendars);
       while (g_hash_table_iter_next (&iter, NULL, (gpointer*) &monitor))
-        gcal_calendar_monitor_set_range (monitor, self->range);
+        gcal_calendar_monitor_set_range (monitor, self->augmented_range);
     }
 
   GCAL_EXIT;
@@ -375,6 +450,9 @@ gcal_timeline_finalize (GObject *object)
   g_clear_pointer (&self->calendars, g_hash_table_destroy);
   g_clear_pointer (&self->subscribers, g_hash_table_destroy);
 
+  g_clear_pointer (&self->augmented_range, gcal_range_unref);
+  g_clear_pointer (&self->range, gcal_range_unref);
+
   G_OBJECT_CLASS (gcal_timeline_parent_class)->finalize (object);
 }
 
@@ -457,6 +535,8 @@ gcal_timeline_class_init (GcalTimelineClass *klass)
 static void
 gcal_timeline_init (GcalTimeline *self)
 {
+  self->augmentation_factor = 1.0;
+
   self->cancellable = g_cancellable_new ();
   self->events = gcal_range_tree_new_with_free_func (g_object_unref);
   self->calendars = g_hash_table_new_full (NULL, NULL, NULL, g_object_unref);
@@ -480,6 +560,25 @@ gcal_timeline_new (void)
                        NULL);
 }
 
+/**
+ * gcal_timeline_new_augmented:
+ *
+ * Creates a new #GcalTimeline that augments its ranges by
+ * @augmentation_factor. This is
+ *
+ * Returns: (transfer full): a #GcalTimeline
+ */
+GcalTimeline*
+gcal_timeline_new_augmented (double augmentation_factor)
+{
+  g_autoptr (GcalTimeline) self = NULL;
+
+  self = g_object_new (GCAL_TYPE_TIMELINE, NULL);
+  self->augmentation_factor = augmentation_factor;
+
+  return g_steal_pointer (&self);
+}
+
 /**
  * gcal_timeline_add_calendar:
  * @self: a #GcalTimeline
@@ -510,8 +609,8 @@ gcal_timeline_add_calendar (GcalTimeline *self,
   g_hash_table_insert (self->calendars, calendar, g_object_ref (monitor));
   g_list_store_append (self->calendar_monitors, monitor);
 
-  if (self->range)
-    gcal_calendar_monitor_set_range (monitor, self->range);
+  if (self->augmented_range)
+    gcal_calendar_monitor_set_range (monitor, self->augmented_range);
 
   update_completed_calendars (self);
 

src/core/gcal-timeline.h

@@ -31,6 +31,8 @@ G_DECLARE_FINAL_TYPE (GcalTimeline, gcal_timeline, GCAL, TIMELINE, GObject)
 
 GcalTimeline*        gcal_timeline_new                           (void);
 
+GcalTimeline*        gcal_timeline_new_augmented                 (double              augmentation_factor);
+
 void                 gcal_timeline_add_calendar                  (GcalTimeline       *self,
                                                                   GcalCalendar       *calendar);