/// <summary>
/// Gets the <see cref="DaylightSavingsRule" /> in effect at a particular <paramref name="moment" />
/// </summary>
/// <param name="standardOffset"></param>
/// <param name="moment"></param>
/// <param name="mostRecentDaylightSavingsRule"></param>
/// <returns></returns>
private bool TryGetMostRecentDaylightSavingsRule(TimeSpan standardOffset, Moment moment,
out DaylightSavingsRule mostRecentDaylightSavingsRule)
{
mostRecentDaylightSavingsRule = null;
DateTime dateTimeOfMoment = moment.ToDateTime();
TimeSpan mostRecentOffsetAdjustment = TimeSpan.Zero;
DaylightSavingsRule mostRecentDaylightSavingsRulePriorToYear;
if (TryGetMostRecentDaylightSavingsRulePriorToYear(dateTimeOfMoment.Year,
out mostRecentDaylightSavingsRulePriorToYear))
{
mostRecentOffsetAdjustment = mostRecentDaylightSavingsRulePriorToYear.AdjustmentToStandardOffset;
mostRecentDaylightSavingsRule = mostRecentDaylightSavingsRulePriorToYear;
}
DaylightSavingsRule mostRecentDaylightSavingsRuleDuringYear;
if (TryGetMostRecentDaylightSavingsRuleDuringYear(standardOffset, mostRecentOffsetAdjustment, moment,
out mostRecentDaylightSavingsRuleDuringYear))
{
mostRecentDaylightSavingsRule = mostRecentDaylightSavingsRuleDuringYear;
}
if (null == mostRecentDaylightSavingsRule)
{
return(false);
}
return(true);
}
private bool TryGetMostRecentDaylightSavingsRuleDuringYear(TimeSpan standardOffset,
TimeSpan mostRecentAdjustmentToStandardOffset, Moment moment,
out DaylightSavingsRule mostRecentDaylightSavingsRule)
{
mostRecentDaylightSavingsRule = null;
DateTime dateTimeOfMoment = moment.ToDateTime();
// get the DaylightSavingsRules from the current year.
IEnumerable <DaylightSavingsRule> currentYearDaylightSavingsRules =
GetAllDaylightSavingsRulesEffectiveInYear(dateTimeOfMoment.Year);
// Guard: current year has no rules
if (!currentYearDaylightSavingsRules.Any())
{
return(false);
}
var momentRulesDictionary = new Dictionary <Moment, DaylightSavingsRule>();
IEnumerable <DaylightSavingsRule> orderedCurrentYearRules =
OrderRulesByDayOfYear(currentYearDaylightSavingsRules,
dateTimeOfMoment.Year);
// initialize offset to offset at end of previous year
TimeSpan effectiveAdjustmentToStandardOffset = mostRecentAdjustmentToStandardOffset;
// determine the Moment each DaylightSavingsRule occurs
foreach (DaylightSavingsRule daylightSavingsRule in orderedCurrentYearRules)
{
Moment momentDaylightSavingsRuleOccurs = daylightSavingsRule.ToMoment(standardOffset,
effectiveAdjustmentToStandardOffset, dateTimeOfMoment.Year);
momentRulesDictionary.Add(momentDaylightSavingsRuleOccurs, daylightSavingsRule);
// update daylight savings adjustment
effectiveAdjustmentToStandardOffset = daylightSavingsRule.AdjustmentToStandardOffset;
}
// locate the most recent rule to have occured this year
int i = 0;
while (momentRulesDictionary.Count > i && momentRulesDictionary.ElementAt(i).Key < moment)
{
mostRecentDaylightSavingsRule = momentRulesDictionary.ElementAt(i).Value;
i++;
}
return(true);
}
private bool TryGetMostRecentDaylightSavingsRulePriorToYear(int year,
out DaylightSavingsRule daylightSavingsRuleInEffectAtStartOfYear)
{
// get the earliest year any rule ever was in effect
int?earliestYearWithEffectiveDaylightSavingsRules;
// Guard: no rule was ever in effect
if (!TryGetEarliestYearWithEffectiveDaylightSavingsRules(out earliestYearWithEffectiveDaylightSavingsRules))
{
daylightSavingsRuleInEffectAtStartOfYear = null;
return(false);
}
// Guard: earliest year any DaylightSavingsRule was in effect is on or after the year we're
// looking to start
if (earliestYearWithEffectiveDaylightSavingsRules.Value >= year)
{
daylightSavingsRuleInEffectAtStartOfYear = null;
return(false);
}
// initialize loop variables
int previousYear = year - 1;
IEnumerable <DaylightSavingsRule> previousYearDaylightSavingsRules =
GetAllDaylightSavingsRulesEffectiveInYear(previousYear);
// walk backwards through the DaylightSavingsRules until we find the most recent year
// in which one or more rules were active
while (!previousYearDaylightSavingsRules.Any())
{
previousYear--;
previousYearDaylightSavingsRules = GetAllDaylightSavingsRulesEffectiveInYear(previousYear);
}
daylightSavingsRuleInEffectAtStartOfYear =
OrderRulesByDayOfYear(previousYearDaylightSavingsRules, previousYear).Last();
return(true);
}
