using CeresSharp;

namespace CeresSharp.Test;

[TestFixture]
public class InterpolatorTests
{
    [Test]
    public void CubicInterpolator_ShouldCreate()
    {
        var data = new double[] { 0.0, 1.0, 4.0, 9.0, 16.0 }; // x^2 values
        using var interpolator = new CubicInterpolator(data);
        
        Assert.That(interpolator, Is.Not.Null);
    }

    [Test]
    public void CubicInterpolator_Evaluate_ShouldReturnValue()
    {
        var data = new double[] { 0.0, 1.0, 4.0, 9.0, 16.0 }; // x^2 values
        using var interpolator = new CubicInterpolator(data);
        
        interpolator.Evaluate(x: 2.5, out double value, out double? gradient);
        
        Assert.That(value, Is.GreaterThan(0.0));
        Assert.That(gradient, Is.Not.Null);
    }

    [Test]
    public void CubicInterpolator_Evaluate_WithoutGradient_ShouldWork()
    {
        var data = new double[] { 0.0, 1.0, 4.0, 9.0, 16.0 };
        using var interpolator = new CubicInterpolator(data);
        
        interpolator.Evaluate(x: 2.0, out double value, out double? gradient);
        
        // At x=2, should be close to 4.0
        Assert.That(Math.Abs(value - 4.0), Is.LessThan(1.0));
    }

    [Test]
    public void BiCubicInterpolator_ShouldCreate()
    {
        // 3x3 grid: values from 0 to 8
        var data = new double[]
        {
            0.0, 1.0, 2.0,
            3.0, 4.0, 5.0,
            6.0, 7.0, 8.0
        };
        using var interpolator = new BiCubicInterpolator(data, rows: 3, cols: 3);
        
        Assert.That(interpolator, Is.Not.Null);
    }

    [Test]
    public void BiCubicInterpolator_Evaluate_ShouldReturnValue()
    {
        var data = new double[]
        {
            0.0, 1.0, 2.0,
            3.0, 4.0, 5.0,
            6.0, 7.0, 8.0
        };
        using var interpolator = new BiCubicInterpolator(data, rows: 3, cols: 3);
        
        interpolator.Evaluate(x: 1.0, y: 1.0, out double value,
            out double? gradientX, out double? gradientY);
        
        Assert.That(value, Is.GreaterThanOrEqualTo(0.0));
        Assert.That(gradientX, Is.Not.Null);
        Assert.That(gradientY, Is.Not.Null);
    }

    [Test]
    public void BiCubicInterpolator_Evaluate_AtGridPoint_ShouldMatch()
    {
        var data = new double[]
        {
            0.0, 1.0, 2.0,
            3.0, 4.0, 5.0,
            6.0, 7.0, 8.0
        };
        using var interpolator = new BiCubicInterpolator(data, rows: 3, cols: 3);
        
        // Evaluate at grid point (1, 1) which should be 4.0
        interpolator.Evaluate(x: 1.0, y: 1.0, out double value,
            out double? gradientX, out double? gradientY);
        
        Assert.That(Math.Abs(value - 4.0), Is.LessThan(0.1));
    }

    [Test]
    public void BiCubicInterpolator_Evaluate_Interpolated_ShouldBeSmooth()
    {
        var data = new double[]
        {
            0.0, 1.0, 2.0,
            3.0, 4.0, 5.0,
            6.0, 7.0, 8.0
        };
        using var interpolator = new BiCubicInterpolator(data, rows: 3, cols: 3);
        
        // Evaluate at interpolated point (0.5, 0.5)
        interpolator.Evaluate(x: 0.5, y: 0.5, out double value1,
            out double? gradientX1, out double? gradientY1);
        
        // Evaluate at nearby point (0.6, 0.6)
        interpolator.Evaluate(x: 0.6, y: 0.6, out double value2,
            out double? gradientX2, out double? gradientY2);
        
        // Values should be close (smooth interpolation)
        Assert.That(Math.Abs(value1 - value2), Is.LessThan(1.0));
    }

    [Test]
    public void BiCubicInterpolator_LargeGrid_ShouldWork()
    {
        // 5x5 grid
        var data = new double[25];
        for (int i = 0; i < 25; i++)
        {
            data[i] = i;
        }
        
        using var interpolator = new BiCubicInterpolator(data, rows: 5, cols: 5);
        
        interpolator.Evaluate(x: 2.5, y: 2.5, out double value,
            out double? gradientX, out double? gradientY);
        
        Assert.That(value, Is.GreaterThanOrEqualTo(0.0));
    }
}