acdream/tests/AcDream.Core.Tests/World/DerethDateTimeTests.cs

using AcDream.Core.World;
using Xunit;

namespace AcDream.Core.Tests.World;

public sealed class DerethDateTimeTests
{
    // ACE calendar anchor: tick 0 = Morningthaw 1, 10 P.Y. at Morntide-and-Half
    // (slot 7 on the 0-indexed 16-slot scale). The DayFraction function
    // applies +7/16 offset so "what time is it in the day" reads correctly.

    [Fact]
    public void DayFraction_AtTick0_IsMorntideAndHalf()
    {
        // Tick 0 = Morntide-and-Half = slot 7 = 7/16 of the day.
        Assert.Equal(7.0 / 16.0, DerethDateTime.DayFraction(0), 4);
    }

    [Fact]
    public void DayFraction_AtHalfDayFromTick0_IsHalf()
    {
        // From tick 0 (slot 7) + half a day = slot 7 + 8 = slot 15 (Gloaming-and-Half).
        // Verify the formula advances by 0.5 correctly: (0 + DayTicks/2) → 7/16 + 1/2 = 15/16.
        Assert.Equal(15.0 / 16.0, DerethDateTime.DayFraction(DerethDateTime.DayTicks / 2), 4);
    }

    [Fact]
    public void DayFraction_WrapsAfterOneDay()
    {
        // Full day from tick 0 returns to the same slot (Morntide-and-Half = 7/16).
        Assert.Equal(7.0 / 16.0, DerethDateTime.DayFraction(DerethDateTime.DayTicks), 4);
    }

    [Fact]
    public void CurrentHour_AtTick0_IsMorntideAndHalf()
    {
        // ACE ref: DerethDateTime.cs:145 — `hour = (int)Hours.Morntide_and_Half;`
        Assert.Equal(DerethDateTime.HourName.MorntideAndHalf, DerethDateTime.CurrentHour(0));
    }

    [Fact]
    public void CurrentHour_AtMidnight_IsDarktide()
    {
        // ACE ref: DerethDateTime.cs:25 — `dayOneTicks = 0 + hourOneTicks + (hourTicks * 8)
        // // Morningthaw 2, 10 P.Y. - Darktide`. From tick 0 to Darktide next day = 4020.
        // Using our slot-based formula: from slot 7 -> slot 0 (wrap) = 9 slots = 9 * 476.25
        // = 4286.25 ticks (slight difference because ACE snaps to quarter hours; our
        // continuous formula is smoother). We verify slot 0 (Darktide) at 9/16 of a day
        // past tick 0.
        double ticks = DerethDateTime.DayTicks * (9.0 / 16.0);
        Assert.Equal(DerethDateTime.HourName.Darktide, DerethDateTime.CurrentHour(ticks));
    }

    [Fact]
    public void CurrentHour_AtNoon_IsMidsong()
    {
        // Midsong is slot 8 on the 16-slot scale. From tick 0 (slot 7) advance by 1 slot.
        double ticks = DerethDateTime.DayTicks * (1.0 / 16.0);
        Assert.Equal(DerethDateTime.HourName.Midsong, DerethDateTime.CurrentHour(ticks));
    }

    [Fact]
    public void IsDaytime_Tick0_True()
    {
        // Morntide-and-Half (slot 7) falls in the daytime band (slots 4..11).
        Assert.True(DerethDateTime.IsDaytime(0));
    }

    [Fact]
    public void IsDaytime_Darktide_False()
    {
        // Darktide = slot 0. Need tick offset of 9/16 from tick 0 to reach it.
        double ticks = DerethDateTime.DayTicks * (9.0 / 16.0);
        Assert.False(DerethDateTime.IsDaytime(ticks));
    }

    [Fact]
    public void ToCalendar_PY10Day1_Morningthaw()
    {
        // Tick 0 maps to PY 10 (= relative year 0 + ZeroYear=10),
        // Morningthaw 1 — matches retail's calendar epoch
        // (ACE DerethDateTime.cs: dayZeroTicks = 0; // Morningthaw 1, 10 P.Y.).
        var cal = DerethDateTime.ToCalendar(0);
        Assert.Equal(DerethDateTime.ZeroYear, cal.Year);
        Assert.Equal(DerethDateTime.MonthName.Morningthaw, cal.Month);
        Assert.Equal(1, cal.Day);
    }

    [Fact]
    public void ToCalendar_AdvancesCorrectly()
    {
        // One year from start → PY (10 + 1) = 11, Morningthaw 1.
        var cal = DerethDateTime.ToCalendar(DerethDateTime.YearTicks);
        Assert.Equal(DerethDateTime.ZeroYear + 1, cal.Year);
        Assert.Equal(DerethDateTime.MonthName.Morningthaw, cal.Month);
        Assert.Equal(1, cal.Day);

        // One month into year 11 → Solclaim (next month after Morningthaw).
        var cal2 = DerethDateTime.ToCalendar(DerethDateTime.YearTicks + DerethDateTime.MonthTicks);
        Assert.Equal(DerethDateTime.ZeroYear + 1, cal2.Year);
        Assert.Equal(DerethDateTime.MonthName.Solclaim, cal2.Month);
    }

    [Fact]
    public void ToCalendar_TickAtSeedsow24Year106_MatchesRetailFormat()
    {
        // Regression guard for the 2026-04-27 dual-client comparison.
        // Retail @timestamp output format is
        //   "Date: <Month> <Day>, <Year> P.Y."
        // Pick a tick at the exact start of Seedsow 24 in relative year 106:
        //   shifted = 106 * YearTicks + 2 * MonthTicks + 23 * DayTicks
        // Derived: 290,779,200 + 457,200 + 175,260 = 291,411,660. Subtract
        // OriginOffsetTicks (3600 in Dereth dat) to get the input tick:
        //   291,411,660 - 3600 = 291,408,060
        // Expected output: PY 116 (= ZeroYear 10 + relative 106), Seedsow,
        // day 24 1-indexed.
        DerethDateTime.SetOriginOffsetFromDat(3600.0);
        try
        {
            var cal = DerethDateTime.ToCalendar(291_408_060.0);
            Assert.Equal(DerethDateTime.ZeroYear + 106, cal.Year);
            Assert.Equal(DerethDateTime.MonthName.Seedsow, cal.Month);
            Assert.Equal(24, cal.Day);
        }
        finally
        {
            DerethDateTime.SetOriginOffsetFromDat(DerethDateTime.DayFractionOriginOffsetTicks);
        }
    }
}