[california/wip/732930-explain] Enforce preconditions when explaining various RRULEs

[Jim Nelson <jnelson src gnome org>]

commit 1ff34543c335bf9d3ed3f2eddbdc8c7bce629fad
Author: Jim Nelson <jim yorba org>
Date:   Fri Sep 5 15:34:23 2014 -0700

    Enforce preconditions when explaining various RRULEs

 src/component/component-recurrence-rule.vala |   31 ++++++++++++++++++-------
 1 files changed, 22 insertions(+), 9 deletions(-)
---
diff --git a/src/component/component-recurrence-rule.vala b/src/component/component-recurrence-rule.vala
index 5428ffb..0a9286c 100644
--- a/src/component/component-recurrence-rule.vala
+++ b/src/component/component-recurrence-rule.vala
@@ -600,12 +600,12 @@ public class RecurrenceRule : BaseObject {
                 return explain_weekly(ngettext("week", "%d weeks", interval).printf(interval));
             
             case iCal.icalrecurrencetype_frequency.MONTHLY_RECURRENCE:
-                Gee.Set<ByRule> active = get_active_by_rules();
-                bool has_byday = active.contains(ByRule.DAY);
-                bool has_bymonthday = active.contains(ByRule.MONTH_DAY);
+                Gee.Set<ByRule> byrules = get_active_by_rules();
+                bool has_byday = byrules.contains(ByRule.DAY);
+                bool has_bymonthday = byrules.contains(ByRule.MONTH_DAY);
                 
                 // requires one and only one
-                if (has_byday == has_bymonthday || active.size > 1)
+                if (has_byday == has_bymonthday || byrules.size != 1)
                     return null;
                 
                 string unit = ngettext("month", "%d months", interval).printf(interval);
@@ -624,7 +624,11 @@ public class RecurrenceRule : BaseObject {
         
     }
     
-    private string explain_daily(string units) {
+    private string? explain_daily(string units) {
+        // only explain basic DAILY RRULEs
+        if (get_active_by_rules().size != 0)
+            return null;
+        
         if (count > 0) {
             // As in, "Repeats every day, 2 times"
             return _("Repeats every %s, %s").printf(units,
@@ -699,9 +703,9 @@ public class RecurrenceRule : BaseObject {
     }
     
     private string? explain_weekly(string units) {
-        // can only explain BYDAY rules
-        Gee.Set<ByRule> active = get_active_by_rules();
-        if (!active.contains(ByRule.DAY) || active.size == 0)
+        // can only explain WEEKLY BYDAY rules
+        Gee.Set<ByRule> byrules = get_active_by_rules();
+        if (byrules.size != 1 || !byrules.contains(ByRule.DAY))
             return null;
         
         string? days_of_the_week = explain_days_of_the_week();
@@ -812,6 +816,11 @@ public class RecurrenceRule : BaseObject {
     }
     
     private string? explain_monthly_bymonthday(string units) {
+        // only MONTHLY BYDAY RRULEs
+        Gee.Set<int> byrules = get_active_by_rules();
+        if (byrules.size != 1 || !byrules.contains(ByRule.MONTH_DAY))
+            return null;
+        
         // currently only support one monthday (generally, the same as DTSTART)
         Gee.Set<int> monthdays = get_by_rule(ByRule.MONTH_DAY);
         if (monthdays.size != 1)
@@ -846,7 +855,11 @@ public class RecurrenceRule : BaseObject {
         return _("Repeats every %s on %s").printf(units, day);
     }
     
-    private string explain_yearly(string units, Calendar.Date start_date) {
+    private string? explain_yearly(string units, Calendar.Date start_date) {
+        // only explain basic YEARLY RRULEs
+        if (get_active_by_rules().size != 0)
+            return null;
+        
         string date = start_date.to_pretty_string(
             Calendar.Date.PrettyFlag.NO_DAY_OF_WEEK
             | Calendar.Date.PrettyFlag.NO_TODAY