refactor(runtime): own world environment state

src/AcDream.Core/World/DerethCalendar.cs

@@ -0,0 +1,103 @@
+namespace AcDream.Core.World;
+
+/// <summary>
+/// Instance-scoped Dereth calendar projection. Retail stores the Region
+/// <c>GameTime.ZeroTimeOfYear</c> beside the active world rather than in a
+/// process-global calendar. Keeping that origin on this object lets multiple
+/// Runtime sessions use different Region definitions without corrupting one
+/// another.
+/// </summary>
+public sealed class DerethCalendar
+{
+    public DerethCalendar(
+        double originOffsetTicks = DerethDateTime.DayFractionOriginOffsetTicks)
+    {
+        SetOriginOffset(originOffsetTicks);
+    }
+
+    public double OriginOffsetTicks { get; private set; }
+
+    /// <summary>
+    /// Installs the Region DAT origin for this world lifetime.
+    /// </summary>
+    public void SetOriginOffset(double originOffsetTicks)
+    {
+        if (!double.IsFinite(originOffsetTicks))
+            throw new ArgumentOutOfRangeException(nameof(originOffsetTicks));
+
+        OriginOffsetTicks = originOffsetTicks;
+    }
+
+    public double DayFraction(double ticks)
+    {
+        double shifted = Shift(ticks);
+        double rem = shifted
+            - Math.Floor(shifted / DerethDateTime.DayTicks)
+            * DerethDateTime.DayTicks;
+        return rem / DerethDateTime.DayTicks;
+    }
+
+    public DerethDateTime.HourName CurrentHour(double ticks)
+    {
+        int slot = (int)Math.Floor(
+            DayFraction(ticks) * DerethDateTime.HoursInADay);
+        slot = Math.Clamp(slot, 0, DerethDateTime.HoursInADay - 1);
+        return (DerethDateTime.HourName)slot;
+    }
+
+    public bool IsDaytime(double ticks)
+    {
+        int hour = (int)CurrentHour(ticks);
+        return hour >= (int)DerethDateTime.HourName.Dawnsong
+            && hour <= (int)DerethDateTime.HourName.WarmtideAndHalf;
+    }
+
+    public DerethDateTime.Calendar ToCalendar(double ticks)
+    {
+        double shifted = Shift(ticks);
+        int relativeYear = (int)(shifted / DerethDateTime.YearTicks);
+        double withinYear =
+            shifted - relativeYear * DerethDateTime.YearTicks;
+        int month = Math.Min(
+            DerethDateTime.MonthsInAYear - 1,
+            (int)(withinYear / DerethDateTime.MonthTicks));
+        double withinMonth =
+            withinYear - month * DerethDateTime.MonthTicks;
+        int day = Math.Min(
+            DerethDateTime.DaysInAMonth,
+            (int)(withinMonth / DerethDateTime.DayTicks) + 1);
+
+        return new DerethDateTime.Calendar(
+            relativeYear + DerethDateTime.ZeroYear,
+            (DerethDateTime.MonthName)month,
+            day,
+            CurrentHour(ticks));
+    }
+
+    public int Year(double ticks) =>
+        (int)(Shift(ticks) / DerethDateTime.YearTicks);
+
+    public int AbsoluteYear(double ticks) =>
+        Year(ticks) + DerethDateTime.ZeroYear;
+
+    public int DayOfYear(double ticks)
+    {
+        double shifted = Shift(ticks);
+        int year = (int)(shifted / DerethDateTime.YearTicks);
+        double withinYear =
+            shifted - year * DerethDateTime.YearTicks;
+        return Math.Clamp(
+            (int)(withinYear / DerethDateTime.DayTicks),
+            0,
+            DerethDateTime.DaysInAMonth
+                * DerethDateTime.MonthsInAYear
+                - 1);
+    }
+
+    private double Shift(double ticks)
+    {
+        if (!double.IsFinite(ticks))
+            throw new ArgumentOutOfRangeException(nameof(ticks));
+        return Math.Max(0d, ticks) + OriginOffsetTicks;
+    }
+}