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// Math.NET Numerics, part of the Math.NET Project
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using System;
using Complex = System.Numerics.Complex;
using MathNet.Numerics.Distributions;
using MathNet.Numerics.Providers.FourierTransform;
using MathNet.Numerics.Statistics;
using NUnit.Framework;

namespace MathNet.Numerics.UnitTests.Providers.FourierTransform
{
    /// <summary>
    /// Fourier transform provider tests.
    /// </summary>
    [TestFixture, Category("LAProvider")]
    public class FourierTransformProviderTests
    {
        [Test]
        public void ProviderSurvivesFreeResources()
        {
            var samples = Generate.PeriodicMap(16, w => new Complex(Math.Sin(w), 0), 16, 1.0, Constants.Pi2);

            var spectrum1 = new Complex[samples.Length];
            samples.Copy(spectrum1);
            FourierTransformControl.Provider.Forward(spectrum1, FourierTransformScaling.ForwardScaling);

            FourierTransformControl.FreeResources();

            var spectrum2 = new Complex[samples.Length];
            samples.Copy(spectrum2);
            FourierTransformControl.Provider.Forward(spectrum2, FourierTransformScaling.ForwardScaling);

            for (var i = 0; i < spectrum1.Length; i++)
            {
                Assert.AreEqual(spectrum1[i], spectrum2[i]);
            }
        }

        [Test]
        public void ForwardInplaceRealSine()
        {
            var samples = Generate.PeriodicMap(16, w => new Complex(Math.Sin(w), 0), 16, 1.0, Constants.Pi2);
            var spectrum = new Complex[samples.Length];

            // real-odd transforms to imaginary odd
            samples.Copy(spectrum);
            FourierTransformControl.Provider.Forward(spectrum, FourierTransformScaling.BackwardScaling);

            // all real components must be zero
            foreach (var c in spectrum)
            {
                Assert.AreEqual(0, c.Real, 1e-12, "real");
            }

            // all imaginary components except second and last musth be zero
            for (var i = 0; i < spectrum.Length; i++)
            {
                if (i == 1)
                {
                    Assert.AreEqual(-8, spectrum[i].Imaginary, 1e-12, "imag second");
                }
                else if (i == spectrum.Length - 1)
                {
                    Assert.AreEqual(8, spectrum[i].Imaginary, 1e-12, "imag last");
                }
                else
                {
                    Assert.AreEqual(0, spectrum[i].Imaginary, 1e-12, "imag");
                }
            }
        }

        [TestCase(0x1000)]
        [TestCase(0x7FF)]
        public void ForwardInplaceParsevalTheorem(int count)
        {
            var samples = Generate.RandomComplex(count, GetUniform(1));
            var timeSpaceEnergy = Generate.Map(samples, s => s.MagnitudeSquared()).Mean();

            FourierTransformControl.Provider.Forward(samples, FourierTransformScaling.SymmetricScaling);
            var frequencySpaceEnergy = Generate.Map(samples, s => s.MagnitudeSquared()).Mean();

            Assert.AreEqual(timeSpaceEnergy, frequencySpaceEnergy, 1e-12);
        }

        IContinuousDistribution GetUniform(int seed)
        {
            return new ContinuousUniform(-1, 1, new System.Random(seed));
        }

    }
}
