using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Iris
{
    public class Classificator
    {
        private int featureCount;

        private string positiveResult;

        private double[] weights;

        private readonly double learningRate;

        public Classificator(int featureCount,string positiveResult,double learningRate=0.5)
        {
            this.featureCount = featureCount;

            this.positiveResult = positiveResult;

            this.learningRate = learningRate;

            InitWeight(featureCount);
        }

        private void InitWeight(int featureCount)
        {
            //+1 for bias weight

            weights = new double[featureCount+1];

            for (int i=0;i<weights.Length;i++)
            {
                //weights[i] = new Random().NextDouble();

                weights[i] = 0.5;
            }
        }

        public void Train(Data[] data,int epoch)
        {
            for (int i = 0; i < epoch; i++)
            {
                BatchGraidentDescent(data);
            }
        }

        private void BatchGraidentDescent(Data[] data)
        {
            double wholeSum = WholeSum(data);

            double[] newWeights = new double[weights.Length];

            double tmp = learningRate * (1.0 / data.Length) * wholeSum;

            for (int i=0;i<weights.Length;i++)
            {
                double[] newFeature = GetNewFeature(data[i].Features);

                newWeights[i] = weights[i] - (tmp * newFeature[i]);
            }

            ChangeWeight(newWeights);

        }


        private double WholeSum(Data[] data)
        {
            double wholeSum = 0;

            for(int i=0;i<data.Length;i++)
            {
                wholeSum = Calculate(data[i].Features)-ToY(data[i].Classifcation);
            }

            return wholeSum;
        }

        public double Cost(Data[] data)
        {
            int m = data.Length;

            double cost = 0;

            for(int i=0;i<m;i++)
            {
                double y = ToY(data[i].Classifcation);

                double hypoSum=Calculate(data[i].Features);

                cost+=(y * Math.Log(hypoSum)) + ((1 - y) * Math.Log(1 - hypoSum));
            }

            return (-1.0*(1.0/m)*cost);
        }

        public double Calculate(double[] features)
        {
            if(features.Length!=featureCount)
            {
                throw new ArgumentException("Invalid feature count");
            }

            double[] newFeature = GetNewFeature(features);

            double sum = 0;

            for(int i=0;i< newFeature.Length;i++)
            {
                sum += newFeature[i] * weights[i];
            }

            return Sigmoid(sum);
        }

        private double Sigmoid(double hypoSum)
        {
            double exponent=Math.Exp(hypoSum * -1.0);

            return (1.0 / (1.0 + exponent));
        }

        private void ChangeWeight(double[] newWeights)
        {
            for(int i=0;i<weights.Length;i++)
            {
                weights[i] = newWeights[i];
            }
        }

        /// <summary>
        /// Change multiclass to the output that logistic regression know
        /// </summary>
        /// <param name="output"></param>
        /// <returns></returns>
        private double ToY(string output)
        {
            if(output==positiveResult)
            {
                return 1.0;
            }

            return 0.0;
        }

        /// <summary>
        /// Add a bias input
        /// </summary>
        /// <param name="features"></param>
        /// <returns></returns>
        private double[] GetNewFeature(double[] features)
        {
            double[] newFeature = new double[features.Length + 1];

            //bias input

            newFeature[0] = 1;

            for (int i = 1; i < newFeature.Length; i++)
            {
                newFeature[i] = features[i - 1];
            }

            return newFeature;
        }

        public string GetPositiveResult()
        {
            return positiveResult;
        }
    }
}