/// <summary>
/// This method is used to convert an ISO 8601 formatted date string to a DateTime value that it
/// represents.
/// </summary>
/// <param name="dateTimeText">The ISO 8601 formatted date to parse.</param>
/// <param name="toLocalTime">If true and the string is in a universal time format, the value is
/// converted to local time before being returned. If false, it is returned as a universal time
/// value.</param>
/// <returns>The specified string converted to a local date/time</returns>
/// <exception cref="ArgumentException">This is thrown if the specified date/time string is not valid</exception>
/// <remarks><para>The <see cref="System.DateTime.Parse(string)"/> method is capable of parsing a string
/// in a very specific layout of the ISO 8601 format (SortableDateTimePattern). However, if the string
/// deviates even slightly from that pattern, it cannot be parsed. This method takes an ISO 8601
/// formatted date string in any of various formats and returns the DateTime value that it represents.</para>
///
/// <para>This method does not handle all possible forms of the ISO 8601 format, just those related to
/// date and time values (<c>YYYY-MM-DDTHH:MM:SS.MMMM+HH:MM</c>). Date and time separators (except the
/// 'T') are optional as is the time zone specifier. The time indicator ('T') and the time value can be
/// omitted entirely if not needed. A 'Z' (Zulu) can appear in place of the time zone specifier to
/// indicate universal time. Date/times in universal time format or with a time zone offset are
/// converted to local time if the <c>bToLocalTime</c> parameter is set to true. All other values are
/// assumed to be local time already and will be returned unmodified as are date-only values.</para></remarks>
public static DateTime FromISO8601String(string dateTimeText, bool toLocalTime)
{
DateTime convertedDate;
int year, day, month, hour = 0, minutes = 0, wholeSeconds = 0, milliseconds = 0;
double fracSeconds;
Match m = reISO8601.Match(dateTimeText);
if(!m.Success)
throw new ArgumentException(LR.GetString("ExDUBadISOFormat"), "dateTimeText");
// Day parts must be there
year = Convert.ToInt32(m.Groups["Year"].Value, CultureInfo.InvariantCulture);
month = Convert.ToInt32(m.Groups["Month"].Value, CultureInfo.InvariantCulture);
day = Convert.ToInt32(m.Groups["Day"].Value, CultureInfo.InvariantCulture);
// Time parts are optional
if(m.Groups["Hour"].Value.Length != 0)
{
hour = Convert.ToInt32(m.Groups["Hour"].Value, CultureInfo.InvariantCulture);
if(m.Groups["Minutes"].Value.Length != 0)
{
minutes = Convert.ToInt32(m.Groups["Minutes"].Value, CultureInfo.InvariantCulture);
if(m.Groups["Seconds"].Value.Length != 0)
{
fracSeconds = Convert.ToDouble(m.Groups["Seconds"].Value, CultureInfo.InvariantCulture);
wholeSeconds = (int)fracSeconds;
milliseconds = (int)((fracSeconds - wholeSeconds) * 1000);
}
}
}
convertedDate = new DateTime(year, month, day);
// Sometimes we get something like 240000 to represent the time for a whole day. By adding the time
// parts as a time span, we bypass any potential problems with the DateTime() constructor that
// expects the time parts to be within bounds.
convertedDate += new TimeSpan(0, hour, minutes, wholeSeconds, milliseconds);
// Convert to local time if necessary
if(m.Groups["Zulu"].Value.Length != 0)
{
if(toLocalTime)
convertedDate = convertedDate.ToLocalTime();
}
else
if(m.Groups["TZHours"].Value.Length != 0)
{
// If a time zone offset was specified, add it to the time to get UTC
hour = Convert.ToInt32(m.Groups["TZHours"].Value, CultureInfo.InvariantCulture);
if(m.Groups["TZMinutes"].Value.Length == 0)
minutes = 0;
else
minutes = Convert.ToInt32(m.Groups["TZMinutes"].Value, CultureInfo.InvariantCulture);
convertedDate = convertedDate.AddMinutes(0 - (hour * 60 + minutes));
if(toLocalTime)
convertedDate = convertedDate.ToLocalTime();
}
return convertedDate;
}
