using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MathNet.Numerics.LinearAlgebra;

namespace MathNet.Numerics.UnitTests.OptimizationTests.TestFunctions
{
    public abstract class BaseTestFunction : ITestFunction
    {
        public abstract string Description { get; }
        public abstract int ParameterDimension { get; }
        public abstract int ItemDimension { get; }

        public abstract double ItemValue(Vector<double> x, int itemIndex);
        public abstract void ItemGradientByRef(Vector<double> x, int itemIndex, Vector<double> output);
        public abstract void ItemHessianByRef(Vector<double> x, int itemIndex, Matrix<double> output);

        public virtual Vector<double> ItemGradient(Vector<double> x, int itemIndex)
        {
            var output = new LinearAlgebra.Double.DenseVector(this.ParameterDimension);
            this.ItemGradientByRef(x, itemIndex, output);
            return output;
        }
        
        public virtual Matrix<double> ItemHessian(Vector<double> x, int itemIndex)
        {
            var output = new LinearAlgebra.Double.DenseMatrix(this.ParameterDimension, this.ParameterDimension);
            this.ItemHessianByRef(x, itemIndex, output);
            return output;
        }


        public virtual void JacobianbyRef(Vector<double> x, Matrix<double> output)
        {
            for (int ii = 0; ii < this.ItemDimension; ++ii)
            {
                var grad = this.ItemGradient(x, ii);
                output.SetRow(ii, grad);
            }
        }

        public virtual Matrix<double> Jacobian(Vector<double> x)
        {
            var output = new LinearAlgebra.Double.DenseMatrix(this.ItemDimension, this.ParameterDimension);
            this.JacobianbyRef(x, output);
            return output;
        }

        public virtual void SsqGradientByRef(Vector<double> x, Vector<double> output)
        {
            if (output.Count != this.ParameterDimension)
                throw new ArgumentException($"Output vector must match parameter dimension of function; expected {this.ParameterDimension}, got {output.Count}.");

            for (int jj = 0; jj < this.ParameterDimension; ++jj)
                output[jj] = 0.0;
            var tmp_grad = new LinearAlgebra.Double.DenseVector(this.ParameterDimension);
            double tmp_value = 0.0;

            for (int ii = 0; ii < this.ItemDimension; ++ii)
            {
                tmp_value = this.ItemValue(x, ii);
                this.ItemGradientByRef(x, ii, tmp_grad);
                for (int jj = 0; jj < this.ParameterDimension; ++jj)
                    output[jj] += 2 * tmp_value * tmp_grad[jj];
            }
        }

        public virtual Vector<double> SsqGradient(Vector<double> x)
        {
            var output = new LinearAlgebra.Double.DenseVector(this.ParameterDimension);
            this.SsqGradientByRef(x, output);
            return output;
        }

        public virtual void SsqHessianByRef(Vector<double> x, Matrix<double> output)
        {
            if (output.RowCount != this.ParameterDimension || output.ColumnCount != this.ParameterDimension)
                throw new ArgumentException($"Output matrix must match parameter dimension of function; expected {this.ParameterDimension}x{this.ParameterDimension}, got {output.RowCount}x{output.ColumnCount}.");

            for (int ii = 0; ii < this.ParameterDimension; ++ii)
                for (int jj = 0; jj < this.ParameterDimension; ++jj)
                    output[ii,jj] = 0.0;

            var tmp_grad = new LinearAlgebra.Double.DenseVector(this.ParameterDimension);
            var tmp_hess = new LinearAlgebra.Double.DenseMatrix(this.ParameterDimension, this.ParameterDimension);
            double tmp_value = 0.0;

            for (int ii = 0; ii < this.ItemDimension; ++ii)
            {
                tmp_value = this.ItemValue(x, ii);
                this.ItemGradientByRef(x, ii, tmp_grad);
                this.ItemHessianByRef(x, ii, tmp_hess);
                for (int jj = 0; jj < this.ParameterDimension; ++jj)
                {
                    for (int kk = 0; kk < this.ParameterDimension; ++kk)
                    {
                        var increment = 2 * (tmp_value * tmp_hess[jj, kk] + tmp_grad[jj] * tmp_grad[kk]);
                        output[jj, kk] += increment;
                    }
                }
            }
        }

        public virtual Matrix<double> SsqHessian(Vector<double> x)
        {
            var output = new LinearAlgebra.Double.DenseMatrix(this.ParameterDimension, this.ParameterDimension);
            this.SsqHessianByRef(x, output);
            return output;
        }

        public virtual double SsqValue(Vector<double> x)
        {
            double ssq = 0.0;
            for (int ii = 0; ii < this.ItemDimension; ++ii)
            {
                var tmp = this.ItemValue(x, ii);
                ssq += tmp * tmp;
            }
            return ssq;
        }

    }
}