Convert Recurrence Rule to Descriptive text
Environment
| Product | Telerik WebForms Scheduler for ASP.NET AJAX |
Description
This started as a question in forums, but I will post code sample here as it seems useful.
The goal is to take a RecurrenceRule string from the database for a given appointment and convert that into a plain English statement that could be used in an email for the appointment.
Solution
The shared sample code contains a static class (RecRuleParser) that does this. Usage: RecRuleParser.ParseRRule(<RecurrenceRule string from DB>, <boolean to include exceptions>)
Example 1:
RRULE: DTSTART:20100527T040000Z
DTEND: 20100528T040000Z
RRULE: FREQ=WEEKLY;INTERVAL=1;BYDAY=TH
EXDATE: 20100527T040000Z,20100813T040000Z
RESULT: Occurs weekly every Thursday starting on 5/27/2010 at 12:00 AM except on 5/27/2010 12:00:00 AM and 8/13/2010 12:00:00 AM
Example 2:
RRULE: DTSTART:20100914T180000Z
DTEND: 20100914T190000Z
RRULE: FREQ=MONTHLY;INTERVAL=1;BYSETPOS=4;BYDAY=SA,SU
RESULT: Occurs monthly on the 4th Saturday and Sunday starting on 9/14/2010 at 2:00 PM
Source code:
public static class RecRuleParser
{
public static string ParseRRule(string rRule, bool showExceptions)
{
string parsed = string.Empty;
StringBuilder englishStatement = new StringBuilder();
// Break the input string into basic parts
string[] elements = rRule.Split(' ');
string startDate = elements[0];
string endDate = elements[2];
string recRule = elements[4];
string recExcs = string.Empty;
// Check for exceptions
if (elements.Length > 5)
{
recExcs = elements[6];
}
// Attempt to parse the Zulu dates into DateTime objects
DateTime dtStart = DateTime.ParseExact(GetElemValue(startDate), "yyyyMMddTHHmmssZ", CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal);
DateTime dtEnd = DateTime.ParseExact(GetElemValue(endDate), "yyyyMMddTHHmmssZ", CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal);
TimeSpan tsEnd = dtEnd.Subtract(dtStart);
// Now work with the recurrence rule
Dictionary<string, string> rruleElems = new Dictionary<string, string>();
parsed = GetElemValue(recRule); // Get parsed recurrence rule
elements = parsed.Split(';');
// Convert the string to a dictionary for easy access
for (int i = 0; i < elements.Length; i++)
{
string[] tmp = elements[i].Split('=');
rruleElems.Add(tmp[0], tmp[1]);
}
// Construct English statement based on recurrence rule
englishStatement.Append("Occurs " + rruleElems["FREQ"].ToLower());
string calType = string.Empty;
int timeToAdd = 0;
// Attempt to convert COUNT to integer
try
{
timeToAdd = Convert.ToInt32(rruleElems["COUNT"]);
}
catch
{
timeToAdd = 0;
}
switch (rruleElems["FREQ"].ToLower())
{
case "daily":
// Handle daily recurrence
string[] days = rruleElems["BYDAY"].Split(',');
englishStatement.Append(ParseDayNames(days));
dtEnd = dtEnd.AddDays(timeToAdd);
calType = "days";
break;
case "weekly":
// Handle weekly recurrence
calType = "weeks";
dtEnd = dtEnd.AddDays(timeToAdd * 7);
try
{
days = rruleElems["BYDAY"].Split(',');
englishStatement.Append(ParseDayNames(days));
}
catch
{
throw new Exception("Error while processing Recurrence Rule");
}
break;
case "monthly":
// Handle monthly recurrence
calType = "months";
dtEnd = dtEnd.AddMonths(timeToAdd);
try
{
string bsp = GetDayEnding(rruleElems["BYSETPOS"]);
englishStatement.Append(" on the " + bsp + " " + ParseDayNames(rruleElems["BYDAY"].Split(',')).Replace(" every ", ""));
}
catch
{
string bsp = GetDayEnding(rruleElems["BYMONTHDAY"]);
englishStatement.Append(" on the " + bsp + " day of each month");
}
break;
case "yearly":
// Handle yearly recurrence
calType = "years";
dtEnd = dtEnd.AddYears(timeToAdd);
string mName = CultureInfo.CurrentCulture.DateTimeFormat.GetMonthName(Convert.ToInt32(rruleElems["BYMONTH"]));
try
{
string bsp = GetDayEnding(rruleElems["BYSETPOS"]);
englishStatement.Append(" on the " + bsp + " " + ParseDayNames(rruleElems["BYDAY"].Split(',')).Replace(" every ", "") + " of " + mName);
}
catch
{
string bsp = GetDayEnding(rruleElems["BYMONTHDAY"]);
englishStatement.Append(" on the " + bsp + " day of " + mName);
}
break;
case "hourly":
// Handle hourly recurrence
calType = "hours";
dtEnd = dtEnd.AddHours(timeToAdd);
break;
default:
break;
}
// Add start time to the English statement
englishStatement.Append(" starting on " + dtStart.ToLocalTime().ToShortDateString() + " at " + dtStart.ToLocalTime().ToShortTimeString());
// Add end time to the English statement if COUNT is specified
if (timeToAdd > 0)
{
englishStatement.Append(" for the next " + rruleElems["COUNT"] + " " + calType);
englishStatement.Append(" ending on " + dtEnd.ToLocalTime().ToShortDateString() + " at " + dtStart.AddHours(tsEnd.Hours).ToLocalTime().ToShortTimeString());
}
// Add exception dates to the English statement if present and requested
if (recExcs.Length > 0 && showExceptions)
{
string[] excs = recExcs.Split(':')[1].Split(',');
string retString = string.Empty;
englishStatement.Append(" except on ");
for (int r = 0; r < excs.Length; r++)
{
dtEnd = DateTime.ParseExact(excs[r], "yyyyMMddTHHmmssZ", CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal).ToLocalTime();
if (r < excs.Length && excs.Length > 2)
{
retString += dtEnd + ",";
}
else
{
if (r < excs.Length - 1 && excs.Length == 2)
{
retString += dtEnd + " and ";
}
else
{
retString += dtEnd;
}
}
}
englishStatement.Append(retString);
}
return englishStatement.ToString();
}
private static string GetElemValue(string elem)
{
// Helper function to extract value from element
string[] elems = elem.Split(':');
return elems[1].Trim();
}
private static string GetDayName(string day)
{
// Helper function to get day name
switch (day)
{
case "MO":
return "Monday";
case "TU":
return "Tuesday";
case "WE":
return "Wednesday";
case "TH":
return "Thursday";
case "FR":
return "Friday";
case "SA":
return "Saturday";
case "SU":
return "Sunday";
default:
return "";
}
}
private static string ParseDayNames(string[] days)
{
// Helper function to parse day names
string retString = string.Empty;
if (days.Length < 7)
{
retString += " every";
for (int d = 0; d < days.Length; d++)
{
days[d] = GetDayName(days[d]);
if (d == days.Length - 1 && days.Length > 1)
{
days[d] = " and " + days[d];
}
else
{
if (days.Length > 2)
{
days[d] += ",";
}
}
retString += " " + days[d];
}
}
return retString;
}
private static string GetDayEnding(string d)
{
// Helper function to handle the ordinal suffix for day numbers
if (d.EndsWith("1") && d != "11")
{
d += "st";
}
if (d.EndsWith("2") && d != "12")
{
d += "nd";
}
if (d.EndsWith("3") && d != "13")
{
d += "rd";
}
if (d.Length < 3)
{
d += "th";
}
return d;
}
}