using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using Just.PreciseMath.PerformanceComparison.Reference;

namespace Just.PreciseMath.PerformanceComparison;

/// <summary>
/// Compares Square, Sqrt, and Abs on the same ordinary finite operands across binary64,
/// the <c>Just.PreciseMath</c> double-double, and the blog reference implementation.
/// Every category measures one function, and its binary64 method is the baseline, so
/// the ratio columns read as "times the cost of a double".
/// </summary>
/// <remarks>
/// Operands are independent array elements, so the measurements include loads, stores,
/// and loop overhead on purpose; input construction and fixture validation stay outside
/// the timed methods.
/// </remarks>
[MemoryDiagnoser]
[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
[CategoriesColumn]
public class MathComparisonBenchmarks
{
    private double[] _doublePositive = [];
    private DoubleDouble[] _positive = [];
    private DoubleDoubleSample[] _samplePositive = [];
    private double[] _doubleMixed = [];
    private DoubleDouble[] _mixed = [];
    private DoubleDoubleSample[] _sampleMixed = [];
    private readonly double[] _doubleResults = new double[PerformanceInputs.Count];
    private readonly DoubleDouble[] _results = new DoubleDouble[PerformanceInputs.Count];
    private readonly DoubleDoubleSample[] _sampleResults = new DoubleDoubleSample[PerformanceInputs.Count];

    [GlobalSetup]
    public void Setup()
    {
        PerformanceInputs inputs = PerformanceInputs.Create();
        _doublePositive = inputs.DoublePositive;
        _positive = inputs.Positive;
        _samplePositive = inputs.SamplePositive;
        // Square and Sqrt need positive operands; Abs also covers negative ones.
        _doubleMixed = inputs.DoubleLeft;
        _mixed = inputs.Left;
        _sampleMixed = inputs.SampleLeft;
    }

    [Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
    public double[] DoubleSquare()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _doubleResults[i] = _doublePositive[i] * _doublePositive[i];
        }
        return _doubleResults;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
    public DoubleDouble[] DoubleDoubleSquare()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _results[i] = DoubleDouble.Square(_positive[i]);
        }
        return _results;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Square")]
    public DoubleDoubleSample[] DoubleDoubleSampleSquare()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _sampleResults[i] = _samplePositive[i].Square();
        }
        return _sampleResults;
    }

    [Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
    public double[] DoubleSqrt()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _doubleResults[i] = Math.Sqrt(_doublePositive[i]);
        }
        return _doubleResults;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
    public DoubleDouble[] DoubleDoubleSqrt()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _results[i] = DoubleDouble.Sqrt(_positive[i]);
        }
        return _results;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Sqrt")]
    public DoubleDoubleSample[] DoubleDoubleSampleSqrt()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _sampleResults[i] = _samplePositive[i].Sqrt();
        }
        return _sampleResults;
    }

    [Benchmark(Baseline = true, OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
    public double[] DoubleAbs()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _doubleResults[i] = Math.Abs(_doubleMixed[i]);
        }
        return _doubleResults;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
    public DoubleDouble[] DoubleDoubleAbs()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _results[i] = DoubleDouble.Abs(_mixed[i]);
        }
        return _results;
    }

    [Benchmark(OperationsPerInvoke = PerformanceInputs.Count), BenchmarkCategory("Abs")]
    public DoubleDoubleSample[] DoubleDoubleSampleAbs()
    {
        for (int i = 0; i < PerformanceInputs.Count; i++)
        {
            _sampleResults[i] = _sampleMixed[i].Abs();
        }
        return _sampleResults;
    }
}