1  // Copyright (c) Microsoft Corporation
  2  // The Microsoft Corporation licenses this file to you under the MIT license.
  3  // See the LICENSE file in the project root for more information.
  4  
  5  using System;
  6  
  7  namespace Microsoft.PowerToys.Settings.UI.Library.Helpers
  8  {
  9      public static class SunCalc
 10      {
 11          public static SunTimes CalculateSunriseSunset(double latitude, double longitude, int year, int month, int day)
 12          {
 13              double zenith = 90.833; // official sunrise/sunset
 14  
 15              int n1 = (int)Math.Floor(275.0 * month / 9.0);
 16              int n2 = (int)Math.Floor((month + 9.0) / 12.0);
 17              int n3 = (int)Math.Floor(1.0 + Math.Floor((year - (4.0 * Math.Floor(year / 4.0)) + 2.0) / 3.0));
 18              int n = n1 - (n2 * n3) + day - 30;
 19  
 20              double? riseUT = CalcTime(isSunrise: true);
 21              double? setUT = CalcTime(isSunrise: false);
 22  
 23              var riseLocal = ToLocal(riseUT, year, month, day);
 24              var setLocal = ToLocal(setUT, year, month, day);
 25  
 26              var result = new SunTimes
 27              {
 28                  HasSunrise = riseLocal.HasValue,
 29                  HasSunset = setLocal.HasValue,
 30                  SunriseHour = riseLocal?.Hour ?? -1,
 31                  SunriseMinute = riseLocal?.Minute ?? -1,
 32                  SunsetHour = setLocal?.Hour ?? -1,
 33                  SunsetMinute = setLocal?.Minute ?? -1,
 34              };
 35  
 36              return result;
 37  
 38              // Local functions
 39              double? CalcTime(bool isSunrise)
 40              {
 41                  double lngHour = longitude / 15.0;
 42                  double t = isSunrise ? n + ((6 - lngHour) / 24.0) : n + ((18 - lngHour) / 24.0);
 43  
 44                  double m1 = (0.9856 * t) - 3.289;
 45                  double l = m1 + (1.916 * Math.Sin(Deg2Rad(m1))) + (0.020 * Math.Sin(2 * Deg2Rad(m1))) + 282.634;
 46                  l = NormalizeDegrees(l);
 47  
 48                  double rA = Rad2Deg(Math.Atan(0.91764 * Math.Tan(Deg2Rad(l))));
 49                  rA = NormalizeDegrees(rA);
 50  
 51                  double lquadrant = Math.Floor(l / 90.0) * 90.0;
 52                  double rAquadrant = Math.Floor(rA / 90.0) * 90.0;
 53                  rA = rA + (lquadrant - rAquadrant);
 54                  rA /= 15.0;
 55  
 56                  double sinDec = 0.39782 * Math.Sin(Deg2Rad(l));
 57                  double cosDec = Math.Cos(Math.Asin(sinDec));
 58  
 59                  double cosH = (Math.Cos(Deg2Rad(zenith)) - (sinDec * Math.Sin(Deg2Rad(latitude))))
 60                              / (cosDec * Math.Cos(Deg2Rad(latitude)));
 61  
 62                  if (cosH > 1.0 || cosH < -1.0)
 63                  {
 64                      // Sun never rises or never sets on this date at this location
 65                      return null;
 66                  }
 67  
 68                  double h = isSunrise ? 360.0 - Rad2Deg(Math.Acos(cosH)) : Rad2Deg(Math.Acos(cosH));
 69                  h /= 15.0;
 70  
 71                  double t1 = h + rA - (0.06571 * t) - 6.622;
 72                  double uT = t1 - lngHour;
 73                  uT = NormalizeHours(uT);
 74  
 75                  return uT;
 76              }
 77  
 78              static (int Hour, int Minute)? ToLocal(double? ut, int y, int m, int d)
 79              {
 80                  if (!ut.HasValue)
 81                  {
 82                      return null;
 83                  }
 84  
 85                  // Convert fractional hours to hh:mm with proper rounding
 86                  int hours = (int)Math.Floor(ut.Value);
 87                  int minutes = (int)((ut.Value - hours) * 60.0);
 88  
 89                  // Normalize minute overflow
 90                  if (minutes == 60)
 91                  {
 92                      minutes = 0;
 93                      hours = (hours + 1) % 24;
 94                  }
 95  
 96                  // Build a UTC DateTime on the given date
 97                  var utc = new DateTime(y, m, d, hours, minutes, 0, DateTimeKind.Utc);
 98  
 99                  // Convert to local time using system time zone rules for that date
100                  var local = TimeZoneInfo.ConvertTimeFromUtc(utc, TimeZoneInfo.Local);
101  
102                  return (local.Hour, local.Minute);
103              }
104  
105              static double Deg2Rad(double deg) => deg * Math.PI / 180.0;
106              static double Rad2Deg(double rad) => rad * 180.0 / Math.PI;
107  
108              static double NormalizeDegrees(double angle)
109              {
110                  angle %= 360.0;
111                  if (angle < 0)
112                  {
113                      angle += 360.0;
114                  }
115  
116                  return angle;
117              }
118  
119              static double NormalizeHours(double hours)
120              {
121                  hours %= 24.0;
122                  if (hours < 0)
123                  {
124                      hours += 24.0;
125                  }
126  
127                  return hours;
128              }
129          }
130      }
131  }