[california/wip/732930-explain] Simple start

[Jim Nelson <jnelson src gnome org>]

commit 6a8c970d68da6aa9b8f39a310e29b247565710d9
Author: Jim Nelson <jim yorba org>
Date:   Tue Sep 2 18:21:38 2014 -0700

    Simple start

 src/component/component-recurrence-rule.vala |   48 ++++++++++++++++++++++++++
 1 files changed, 48 insertions(+), 0 deletions(-)
---
diff --git a/src/component/component-recurrence-rule.vala b/src/component/component-recurrence-rule.vala
index 9bd45e3..ee0b293 100644
--- a/src/component/component-recurrence-rule.vala
+++ b/src/component/component-recurrence-rule.vala
@@ -577,6 +577,54 @@ public class RecurrenceRule : BaseObject {
             ical_by_ar[index] = (short) iCal.RECURRENCE_ARRAY_MAX;
     }
     
+    /**
+     * Returns a natural-language string explaining the { link RecurrenceRule} for the user.
+     *
+     * Returns null if the RRULE is beyond the comprehension of this parser.
+     */
+    public string? explain() {
+        string unit;
+        switch (freq) {
+            case iCal.icalrecurrencetype_frequency.DAILY_RECURRENCE:
+                unit = ngettext("day", "%d days", interval);
+            break;
+            
+            case iCal.icalrecurrencetype_frequency.WEEKLY_RECURRENCE:
+                unit = ngettext("week", "%d weeks", interval);
+            break;
+            
+            case iCal.icalrecurrencetype_frequency.MONTHLY_RECURRENCE:
+                unit = ngettext("month", "%d months", interval);
+            break;
+            
+            case iCal.icalrecurrencetype_frequency.YEARLY_RECURRENCE:
+                unit = ngettext("year", "%d years", interval);
+            break;
+            
+            default:
+                return null;
+        }
+        
+        if (count > 0) {
+            return _("Repeats every %s for %s").printf(unit.printf(interval), unit.printf(count));
+        }
+        
+        if (until_date != null) {
+            return _("Repeats every %s until %s").printf(unit.printf(interval),
+                until_date.to_pretty_string(Calendar.Date.PrettyFlag.INCLUDE_YEAR)
+            );
+        }
+        
+        if (until_exact_time != null) {
+            return _("Repeats every %s until %s, %s").printf(unit.printf(interval),
+                until_exact_time.to_pretty_date_string(Calendar.Date.PrettyFlag.INCLUDE_YEAR),
+                until_exact_time.to_pretty_time_string(Calendar.WallTime.PrettyFlag.NONE)
+            );
+        }
+        
+        return _("Repeats every %s").printf(unit.printf(interval));
+    }
+    
     public override string to_string() {
         return "RRULE %s".printf(freq.to_string());
     }