Implement a cache for the monthly view

Add a very simple cache, which is used to store the days that contain an
event or an appointment. This makes redrawing and browsing the calendar
panel much faster.

The cache has a size of 31 integers (which is equivalent to 124 bytes on
a 32 bit system and 248 bytes on a 64 bit system) and invalidates itself
if the current month has changed. If an item is added/changed/removed,
the cache needs to be invalidated manually by calling
calendar_monthly_view_cache_set_invalid(). Note that this will always
invalidate the whole cache, even if only one item at the last day of the
month was removed. This is a trade-off between simplicity and
efficiency.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.c

@@ -369,6 +369,7 @@ int main(int argc, char **argv)
     case KEY_GENERIC_IMPORT:
       wins_erase_status_bar();
       io_import_data(IO_IMPORT_ICAL, NULL);
+      calendar_monthly_view_cache_set_invalid();
       inday = do_storage(0);
       wins_update(FLAG_ALL);
       break;

src/calcurse.h

@@ -144,6 +144,8 @@
 #define DAYINSEC        (DAYINMIN * MININSEC)
 #define HOURINSEC       (HOURINMIN * MININSEC)
 
+#define MAXDAYSPERMONTH 31
+
 /* Calendar window. */
 #define CALHEIGHT       12
 
@@ -629,6 +631,7 @@ void calendar_store_current_date(struct date *);
 void calendar_init_slctd_day(void);
 struct date *calendar_get_slctd_day(void);
 long calendar_get_slctd_day_sec(void);
+void calendar_monthly_view_cache_set_invalid(void);
 void calendar_update_panel(struct window *);
 void calendar_goto_today(void);
 void calendar_change_day(int);

src/calendar.c

@@ -77,6 +77,10 @@ static void (*draw_calendar[CAL_VIEWS]) (struct window *, struct date *,
                                          unsigned) = {
 draw_monthly_view, draw_weekly_view};
 
+static int monthly_view_cache[MAXDAYSPERMONTH];
+static int monthly_view_cache_valid = 0;
+static int monthly_view_cache_month = 0;
+
 /* Switch between calendar views (monthly view is selected by default). */
 void calendar_view_next(void)
 {
@@ -264,6 +268,11 @@ static int date_change(struct tm *date, int delta_month, int delta_day)
   }
 }
 
+void calendar_monthly_view_cache_set_invalid(void)
+{
+  monthly_view_cache_valid = 0;
+}
+
 /* Draw the monthly view inside calendar panel. */
 static void
 draw_monthly_view(struct window *cwin, struct date *current_day,
@@ -313,13 +322,25 @@ draw_monthly_view(struct window *cwin, struct date *current_day,
 
   day_1_sav = (c_day_1 + 1) * 3 + c_day_1 - 7;
 
+  /* invalidate cache if a new month is selected */
+  if (yr * YEARINMONTHS + mo != monthly_view_cache_month) {
+    monthly_view_cache_month = yr * YEARINMONTHS + mo;
+    monthly_view_cache_valid = 0;
+  }
+
   for (c_day = 1; c_day <= numdays; ++c_day, ++c_day_1, c_day_1 %= 7) {
     check_day.dd = c_day;
     check_day.mm = slctd_day.mm;
     check_day.yyyy = slctd_day.yyyy;
 
     /* check if the day contains an event or an appointment */
-    item_this_day = day_check_if_item(check_day);
+    if (monthly_view_cache_valid) {
+      item_this_day = monthly_view_cache[c_day - 1];
+    }
+    else {
+      item_this_day = monthly_view_cache[c_day - 1] =
+        day_check_if_item(check_day);
+    }
 
     /* Go to next line, the week is over. */
     if (!c_day_1 && 1 != c_day) {
@@ -352,6 +373,8 @@ draw_monthly_view(struct window *cwin, struct date *current_day,
       mvwprintw(cwin->p, ofs_y + 1,
                 ofs_x + day_1_sav + 4 * c_day + 1, "%2d", c_day);
   }
+
+  monthly_view_cache_valid = 1;
 }
 
 static int weeknum(const struct tm *t, int firstweekday)

src/interaction.c

@@ -358,6 +358,8 @@ void interact_day_item_edit(void)
     break;
   }
 
+  calendar_monthly_view_cache_set_invalid();
+
   if (need_check_notify)
     notify_check_next_app(1);
 }
@@ -571,6 +573,9 @@ void interact_day_item_add(void)
     if (apoint_hilt() == 0)
       apoint_hilt_increase(1);
   }
+
+  calendar_monthly_view_cache_set_invalid();
+
   wins_erase_status_bar();
 }
 
@@ -613,6 +618,8 @@ void interact_day_item_delete(unsigned *nb_events, unsigned *nb_apoints)
       /* NOTREACHED */
     }
 
+    calendar_monthly_view_cache_set_invalid();
+
     if (apoint_hilt() > 1)
       apoint_hilt_decrease(1);
     if (apad.first_onscreen >= to_be_removed)
@@ -858,6 +865,8 @@ void interact_day_item_repeat(void)
     /* NOTREACHED */
   }
   day_erase_item(date, item_nb, ERASE_FORCE);
+
+  calendar_monthly_view_cache_set_invalid();
 }
 
 /* Free the current cut item, if any. */
@@ -897,6 +906,8 @@ void interact_day_item_cut(unsigned *nb_events, unsigned *nb_apoints)
   day_cut.type = p->type;
   day_cut.item = p->item;
 
+  calendar_monthly_view_cache_set_invalid();
+
   if (p->type == EVNT || p->type == RECUR_EVNT) {
     (*nb_events)--;
     to_be_removed = 1;
@@ -926,6 +937,8 @@ void interact_day_item_paste(unsigned *nb_events, unsigned *nb_apoints)
   item_type = day_paste_item(&day_cut, calendar_get_slctd_day_sec());
   day_cut.type = 0;
 
+  calendar_monthly_view_cache_set_invalid();
+
   if (item_type == EVNT || item_type == RECUR_EVNT)
     (*nb_events)++;
   else if (item_type == APPT || item_type == RECUR_APPT)