equation

namespace Masodfoku
{
    internal class Equation
    {
        private double a, b, c;
        public Equation(double[] values)
        {
            this.a = values[0]; this.b = values[1]; this.c = values[2];
        }

        public Equation(double a, double b, double c)
        {
            this.a = a; this.b = b; this.c = c;
        }

        public double FirstDegreeSolution { get; set; }

        public double[] SecondDegreeSolution { get; set; }

        public string ComplexSolution { get; set; }


        //Eldönti, hogy másodfokú-e az egyenlet. Ha igen, true
        //értékkel tér vissza.
        public bool SecondDegree()
        {
            return this.a != 0 && Determinant() > 0;
        }

        //Eldönti, hogy az egyenlet megoldása csak komplex szám
        //lehet-e. Ehhez az kell, hogy a diszkrimináns negatív legyen.
        public bool Complex()
        {
            return Determinant() < 0;
        }

        public void Solve()
        {
            if (Complex())
            {
                SolveComplex();
            }
            else if (SecondDegree())
            {
                SolveQuadratic();
            }
            else if (this.a == 0 || Determinant() == 0)
            {
                SolveSimple();
            }
            else
            {
                throw new ArgumentException();
            }
        }

        private void SolveQuadratic()
        {
            double partOne = -this.b;
            double partTwo = Math.Sqrt(Determinant());
            double partThree = 2 * this.a;

            this.SecondDegreeSolution = new double[] { (partOne + partTwo) / partThree, (partOne - partTwo) / partThree };
        }

        private void SolveComplex()
        {
            double partOne = -this.b / (2 * this.a);
            double partTwoHelper = Determinant();
            double rootPartTwo = Math.Sqrt(-partTwoHelper);
            double partTwo = rootPartTwo / (2 * this.a);
            this.ComplexSolution = String.Format("{0}+-{1}i", partOne, Math.Round(partTwo, 3));
        }

        private void SolveSimple()
        {
            if (a == 0)
                this.FirstDegreeSolution = -this.c / this.b;
            else if (Determinant() == 0)
                this.FirstDegreeSolution = -this.b / (2 * this.a);
            else
                throw new ArgumentException();
        }

        public override string ToString()
        {
            if (this.Complex())
                return this.ComplexSolution;
            else if (this.SecondDegree())
                return String.Join(", ", this.SecondDegreeSolution);
            else
                return this.FirstDegreeSolution.ToString();
        }

        private double Determinant()
        {
            return Math.Pow(this.b, 2) - 4 * this.a * this.c;
        }
    }
}