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package maths.functions;

import datastructs.IVector;
import datasets.VectorDouble;

public class SigmoidFunction implements IVectorRealFunction> {


    /**
     * Constructor
     * @param function
     */
    public SigmoidFunction(IVectorRealFunction> function){

        this.function = function;
    }

    @Override
    public Double evaluate(IVector input){

        Double value = this.function.evaluate(input);
        double expV = Math.exp(-value);
        return 1.0/(1.0 + expV);
    }

    /**
     * Set the coefficients of the function
     */
    @Override
    public final void setCoeffs(Double[] coeffs){
        this.function.setCoeffs(coeffs);
    }

    /**
     * Set the coefficients of the function
     */
    @Override
    public void setCoeffs(double[] coeffs){
        this.function.setCoeffs(coeffs);
    }

    /**
     * Returns the coefficients of the vector function
     */
    @Override
    public final IVector getCoeffs(){
        return this.function.getCoeffs();
    }

    @Override
    public double getCoeff(int i){
        return this.function.getCoeff(i);
    }

    /**
     * Returns the number of coefficients
     */
    @Override
    public final int numCoeffs(){
        return this.function.numCoeffs();
    }

    /**
     * Returns the gradients with respect to the coefficients at the given data point
     */
    @Override
    public VectorDouble gradidents(IVector data){
        VectorDouble rslt = new VectorDouble(data);
        rslt.set(0, 1.0);
        return rslt;
    }

    /**
     * Returns the gradient with respect to the i-th variable
     * The Sigmoid is assumed to have only one variable. Hence,
     * if i != 0 this function returns 0.0
     */
    @Override
    public double gradient(int i, IVector data){

        if(i != 0){
            return 0.0;
        }

        double z = this.function.evaluate(data);
        double expZ = Math.exp(-z);
        return expZ/((1 + expZ)*(1 + expZ)); //*this.function.gradient(i, data);
    }

    /**
     * Returns the gradient with respect to the i-th coeff
     */
    @Override
    public double coeffGradient(int i, IVector data){

        double z = this.function.evaluate(data);
        double expZ = Math.exp(-z);
        return expZ/((1 + expZ)*(1 + expZ))*this.function.coeffGradient(i, data);
    }

    /**
     * Compute the gradients with respect to the coefficients
     */
    @Override
    public VectorDouble coeffGradients(IVector data){
        VectorDouble grads = new VectorDouble(this.function.numCoeffs(), 0.0);

        for (int i = 0; i < grads.size(); i++) {
            grads.set(i, this.coeffGradient(i, data));
        }

        return grads;
    }


    private IVectorRealFunction> function;
}