namespace GeometriCS
{
    /// <summary>
    /// A line through a two-dimensional vector space.
    /// </summary>
    /// <remarks>
    /// Line follows the equation Ax + By + C = 0
    /// </remarks>
    public class Line2d
    {
        /// <summary>
        /// A coefficient of the line.
        /// </summary>
        /// <remarks>
        /// Line follows the equation Ax + By + C = 0
        /// </remarks>
        public double Coeff_A { get; set; }

        /// <summary>
        /// B coefficient of the line.
        /// </summary>
        /// <remarks>
        /// Line follows the equation Ax + By + C = 0
        /// </remarks>
        public double Coeff_B { get; set; }

        /// <summary>
        /// C coefficient of the line.
        /// </summary>
        /// <remarks>
        /// Line follows the equation Ax + By + C = 0
        /// </remarks>
        public double Coeff_C { get; set; }

        /// <summary>
        /// Construct a line from a point on the line and a direction vector.
        /// </summary>
        /// <param name="pointOnLine">Point that lies on the line.</param>
        /// <param name="direction">Direction the line takes from the point.</param>
        /// <returns>Line2d passing throught the given point with the given direction.</returns>
        public static Line2d FromPointAndDirection(Vector2d pointOnLine, Vector2d direction)
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// Construct a line passing through two given points.
        /// </summary>
        /// <param name="firstPoint">First point that lies on the line.</param>
        /// <param name="secondPoint">Other point that lies on the line.</param>
        /// <returns>Line passing through the two points.</returns>
        public static Line2d FromTwoPoints(Vector2d firstPoint, Vector2d secondPoint)
        {
            (double a, double b, double c) = Utils.Line2CoefficientsFromTwoPoints(firstPoint, secondPoint);
            return new Line2d(a, b, c);
        }

        /// <summary>
        /// Construct the line from its coefficients.
        /// </summary>
        /// <param name="coeff_A"></param>
        /// <param name="coeff_B"></param>
        /// <param name="coeff_C"></param>
        public Line2d(double coeff_A, double coeff_B, double coeff_C)
        {
            Coeff_A = coeff_A;
            Coeff_B = coeff_B;
            Coeff_C = coeff_C;
        }

        /// <summary>
        /// String representation of the line.
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// Do the two objects represent the same line?
        /// </summary>
        /// <param name="obj">Object to compare.</param>
        /// <remarks>
        /// <returns><c>true</c> if the lines have the same coefficients. Otherwise <c>false</c></returns>
        public override bool Equals(object? obj)
        {
            if (obj is Line2d asLn)
            {
                return this == asLn;
            }
            else
            {
                return false;
            }
        }

        public override int GetHashCode()
        {
            return HashCode.Combine(Coeff_A, Coeff_B, Coeff_C);
        }

        /// <summary>
        /// Deep copy the line.
        /// </summary>
        /// <returns>Deep copy of the line.</returns>
        public object Clone()
        {
            return new Line2d(Coeff_A, Coeff_B, Coeff_C);
        }

        /// <summary>
        /// Are the lines equal?
        /// </summary>
        /// <param name="a">First line.</param>
        /// <param name="b">Second line.</param>
        /// <returns><c>true</c> if the lines have the same start and end points. Otherwise <c>false</c></returns>
        public static bool operator ==(Line2d a, Line2d b)
        {
            return Utils.DoubleEquals(a.Coeff_A, b.Coeff_A) && Utils.DoubleEquals(a.Coeff_B, b.Coeff_B) && Utils.DoubleEquals(a.Coeff_C, b.Coeff_C);
        }

        /// <summary>
        /// Are the lines different?
        /// </summary>
        /// <param name="a">First line.</param>
        /// <param name="b">Second line.</param>
        /// <returns><c>true</c> If the lines have the same coefficients. Otherwise <c>false</c>.</returns>
        public static bool operator !=(Line2d a, Line2d b)
        {
            return !(a == b);
        }
    }
}