/// <summary>
/// Compute night fraction value for given high latitude method, angle and sunset/sunrise difference.
/// </summary>
/// <param name="method">
/// <see cref="HighLatitudeAdjustment" /> method to use to get the night fraction.
/// </param>
/// <param name="angle">
/// Sun's angle value to get the night fraction. Only required when <paramref name="method" /> is set to <see cref="HighLatitudeAdjustment.AngleBased" />
/// method.
/// </param>
/// <param name="diff">
/// Difference hour between sunrise to sunset in floating point.
/// </param>
/// <returns>
/// Night fraction value for given high latitude method, angle and sunset/sunrise difference.
/// </returns>
internal static double GetNightFraction(HighLatitudeAdjustment method, double angle, double diff)
{
// Default value to middle of the night method.
double nightFraction;
switch (method)
{
case HighLatitudeAdjustment.MiddleOfNight:
nightFraction = 0.5;
break;
case HighLatitudeAdjustment.OneSeventhOfNight:
nightFraction = 0.14285714285714285;
break;
case HighLatitudeAdjustment.AngleBased:
nightFraction = 0.016666666666666667 * angle;
break;
default:
throw new ArgumentOutOfRangeException(nameof(method));
}
return(nightFraction * diff);
}
/// <summary>
/// Adjust calculated prayer time to high latitude adjustment.
/// </summary>
private static double AdjustForHighLatitude(HighLatitudeAdjustment method, double time, double baseTime, double angle, double diff, Direction direction)
{
// Compute night fraction and duration.
var nightFraction = AstronomyMath.GetNightFraction(method, angle, diff);
var duration = direction == Direction.Clockwise
? DateTimeMath.ComputeDuration(time, baseTime)
: DateTimeMath.ComputeDuration(baseTime, time);
// Copy reference;
var newTime = time;
if (duration > nightFraction)
{
var adjustment = direction == Direction.Clockwise ? nightFraction : -nightFraction;
newTime = baseTime + adjustment;
}
return(newTime);
}
