namespace HSchool.Simulation.Tests;

public class GameClockTests
{
    private static readonly DateTime Start = new(2012, 4, 3, 6, 0, 0, DateTimeKind.Utc);

    private const double OneTwentiethOfASecond = 1d / 20d;
    private const double GameMinutesPerRealSecond = 5d;

    [Fact]
    public void NewClock_StartsRunningAtTheStartDate()
    {
        var clock = new GameClock(Start);

        Assert.Equal(Start, clock.Time);
        Assert.True(clock.IsRunning);
        Assert.Equal(ClockSpeed.DefaultIndex, clock.SpeedIndex);
        Assert.Equal(1d, clock.Multiplier);
    }

    [Fact]
    public void PausedClock_DoesNotMove()
    {
        var clock = new GameClock(Start) { IsRunning = false };

        for (var i = 0; i < 100; i++)
        {
            clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
        }

        Assert.Equal(Start, clock.Time);
    }

    [Fact]
    public void OneRealSecond_AdvancesFiveGameMinutes()
    {
        var clock = new GameClock(Start);

        // One real second at 20 Hz.
        for (var i = 0; i < 20; i++)
        {
            clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
        }

        Assert.Equal(Start.AddMinutes(5), clock.Time);
    }

    [Theory]
    [InlineData(0, 2.5)]
    [InlineData(1, 5)]
    [InlineData(2, 10)]
    [InlineData(3, 15)]
    [InlineData(4, 20)]
    public void SpeedIndex_ScalesTheGameMinutesPerSecond(int speedIndex, double expectedMinutes)
    {
        var clock = new GameClock(Start) { SpeedIndex = speedIndex };

        for (var i = 0; i < 20; i++)
        {
            clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
        }

        Assert.Equal(Start.AddMinutes(expectedMinutes), clock.Time);
    }

    [Theory]
    [InlineData(-1)]
    [InlineData(5)]
    [InlineData(200)]
    public void InvalidSpeedIndex_IsIgnored(int speedIndex)
    {
        var clock = new GameClock(Start) { SpeedIndex = 2 };

        clock.SpeedIndex = speedIndex;

        Assert.Equal(2, clock.SpeedIndex);
    }

    [Fact]
    public void Pausing_FreezesTimeWhereItStopped()
    {
        var clock = new GameClock(Start);
        for (var i = 0; i < 20; i++)
        {
            clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
        }

        var paused = clock.Time;
        clock.IsRunning = false;
        for (var i = 0; i < 100; i++)
        {
            clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
        }

        Assert.Equal(paused, clock.Time);
    }

    [Fact]
    public void SameTickCount_AlwaysProducesTheSameDate()
    {
        Assert.Equal(RunOneHourOfTicks(), RunOneHourOfTicks());

        static DateTime RunOneHourOfTicks()
        {
            var clock = new GameClock(Start) { SpeedIndex = 0 };
            for (var i = 0; i < 20 * 60 * 60; i++)
            {
                clock.Advance(OneTwentiethOfASecond, GameMinutesPerRealSecond);
            }

            return clock.Time;
        }
    }

    [Fact]
    public void Time_IsUtcSoSerializationIsUnambiguous()
    {
        var clock = new GameClock(new DateTime(2012, 4, 3, 6, 0, 0, DateTimeKind.Unspecified));

        Assert.Equal(DateTimeKind.Utc, clock.Time.Kind);
    }

    [Fact]
    public void StartDateOutsideTheSupportedRange_Throws()
    {
        Assert.Throws<ArgumentOutOfRangeException>(() => new GameClock(new DateTime(1800, 1, 1, 0, 0, 0, DateTimeKind.Utc)));
    }
}