using MrGameEng.AI;
using Xunit;

namespace MrGameEng.AI.Tests;

public class SuitabilityTests
{
    [Fact]
    public void Gaussian_PeaksAtOptimum()
    {
        Assert.Equal(1f, Suitability.Gaussian(18f, optimum: 18f, tolerance: 5f), 5);
    }

    [Fact]
    public void Gaussian_IsSymmetricAroundOptimum()
    {
        var below = Suitability.Gaussian(13f, optimum: 18f, tolerance: 5f);
        var above = Suitability.Gaussian(23f, optimum: 18f, tolerance: 5f);
        Assert.Equal(below, above, 5);
    }

    [Fact]
    public void Gaussian_AtOneToleranceAway_IsAboutPoint607()
    {
        Assert.Equal(MathF.Exp(-0.5f), Suitability.Gaussian(23f, 18f, 5f), 5);
    }

    [Fact]
    public void Gaussian_FallsOffWithDistance()
    {
        var near = Suitability.Gaussian(20f, 18f, 5f);
        var far = Suitability.Gaussian(30f, 18f, 5f);
        Assert.True(far < near && far > 0f);
    }

    [Fact]
    public void Gaussian_StaysWithinUnitRange()
    {
        for (var v = -50f; v <= 50f; v += 1f)
        {
            Assert.InRange(Suitability.Gaussian(v, 0f, 7f), 0f, 1f);
        }
    }

    [Fact]
    public void Gaussian_NonPositiveTolerance_IsExactMatch()
    {
        Assert.Equal(1f, Suitability.Gaussian(5f, 5f, 0f));
        Assert.Equal(0f, Suitability.Gaussian(6f, 5f, 0f));
    }

    [Fact]
    public void Trapezoid_IsFlatAcrossThePlateau()
    {
        Assert.Equal(1f, Suitability.Trapezoid(10f, 0f, 10f, 42f, 58f), 5);
        Assert.Equal(1f, Suitability.Trapezoid(25f, 0f, 10f, 42f, 58f), 5);
        Assert.Equal(1f, Suitability.Trapezoid(42f, 0f, 10f, 42f, 58f), 5);
    }

    [Fact]
    public void Trapezoid_RampsLinearlyOnEachShoulder()
    {
        Assert.Equal(0.5f, Suitability.Trapezoid(5f, 0f, 10f, 42f, 58f), 5); // halfway up the cold ramp
        Assert.Equal(0.5f, Suitability.Trapezoid(50f, 0f, 10f, 42f, 58f), 5); // halfway down the heat ramp
    }

    [Fact]
    public void Trapezoid_IsZeroAtAndBeyondTheHardLimits()
    {
        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 10f, 42f, 58f));
        Assert.Equal(0f, Suitability.Trapezoid(-5f, 0f, 10f, 42f, 58f));
        Assert.Equal(0f, Suitability.Trapezoid(58f, 0f, 10f, 42f, 58f));
        Assert.Equal(0f, Suitability.Trapezoid(70f, 0f, 10f, 42f, 58f));
    }

    [Fact]
    public void Trapezoid_DegenerateShoulder_IsAHardStep()
    {
        // optimalLow == min: full suitability immediately above the lower limit, zero at/below it.
        Assert.Equal(1f, Suitability.Trapezoid(5f, 0f, 0f, 10f, 20f));
        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 0f, 10f, 20f));
    }

    [Fact]
    public void Trapezoid_StaysWithinUnitRange()
    {
        for (var v = -50f; v <= 80f; v += 1f)
        {
            Assert.InRange(Suitability.Trapezoid(v, 0f, 10f, 42f, 58f), 0f, 1f);
        }
    }
}