namespace GeometriCS
{
    /// <summary>
    /// Euclidean plane with double precision.
    /// </summary>
    /// <remarks>
    /// Plane follows the equation Ax + By + Cz - D = 0
    /// </remarks>
    public class Planed
    {
        /// <summary>
        /// A coefficient of the plane.
        /// </summary>
        /// <remarks>
        /// Plane follows the equation Ax + By + Cz - D = 0
        /// </remarks>
        public double Coeff_A { get; set; }

        /// <summary>
        /// B coefficient of the plane.
        /// </summary>
        /// <remarks>
        /// Plane follows the equation Ax + By + Cz - D = 0
        /// </remarks>
        public double Coeff_B { get; set; }

        /// <summary>
        /// C coefficient of the plane.
        /// </summary>
        /// <remarks>
        /// Plane follows the equation Ax + By + Cz - D = 0
        /// </remarks>
        public double Coeff_C { get; set; }

        /// <summary>
        /// D coefficient of the plane.
        /// </summary>
        /// <remarks>
        /// Plane follows the equation Ax + By + Cz - D = 0
        /// </remarks>
        public double Coeff_D { get; set; }

        /// <summary>
        /// Normal vector to the plane.
        /// </summary>
        public Vector3d Normal => new Vector3d(Coeff_A, Coeff_B, Coeff_C);

        /// <summary>
        /// Distance of the plane from origin along the normal vector. (signed!)
        /// </summary>
        public double Distance => -Coeff_D;

        /// <summary>
        /// Construct the plane from its normal and distance from origin.
        /// </summary>
        /// <param name="normal">Normal vector of the plane.</param>
        /// <param name="distance">Distance from origin along normal.</param>
        public Planed(Vector3d normal, double distance)
        {
            Coeff_A = normal.X; 
            Coeff_B = normal.Y; 
            Coeff_C = normal.Z; 
            Coeff_D = -distance;
        }

        /// <summary>
        /// Construct the plane from its normal and distance from origin.
        /// </summary>
        /// <param name="coeff_a">A coefficient of the plane.</param>
        /// <param name="coeff_b">B coefficient of the plane.</param>
        /// <param name="coeff_c">C coefficient of the plane.</param>
        /// <param name="coeff_d">D coefficient of the plane.</param>
        /// <remarks>
        /// Plane follows the equation Ax + By + Cz - D = 0
        /// </remarks>
        public Planed(double coeff_a, double coeff_b, double coeff_c, double coeff_d)
        {
            Coeff_A = coeff_a;
            Coeff_B = coeff_b;
            Coeff_C = coeff_c;
            Coeff_D = coeff_d;
        }

        /// <summary>
        /// String representation of the plane.
        /// </summary>
        /// <returns>(normal vector, distance from origin)</returns>
        public override string ToString()
        {
            return $"({Normal}, {Distance})";
        }

        /// <summary>
        /// Do the two objects represent the same plane?
        /// </summary>
        /// <param name="obj">Object to compare.</param>
        /// <remarks>
        /// If the planes have inverse normals and also inverse distances, they are considered not equal despite looking the same.
        /// </remarks>
        /// <returns><c>true</c> If the planes have the same coefficients. <c>false</c></returns>
        public override bool Equals(object? obj)
        {
            if (obj is Planed asPlane)
            {
                return this == asPlane;
            }
            else
            {
                return false;
            }
        }

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

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

        /// <summary>
        /// Are the planes equal?
        /// </summary>
        /// <param name="a">First plane.</param>
        /// <param name="b">Second plane.</param>
        /// <remarks>
        /// If the planes have inverse normals and also inverse distances, they are considered not equal despite looking the same.
        /// </remarks>
        /// <returns><c>true</c> If the planes have the same coefficients. <c>false</c></returns>
        public static bool operator ==(Planed a, Planed b)
        {
            return a.Coeff_A == b.Coeff_A && a.Coeff_B == b.Coeff_B &&
                a.Coeff_C == b.Coeff_C && a.Coeff_D == b.Coeff_D;
        }

        /// <summary>
        /// Are the planes different?
        /// </summary>
        /// <param name="a">First plane.</param>
        /// <param name="b">Second plane.</param>
        /// <returns><c>true</c> If either the normals or the distance differs, otherwise <c>false</c>.</returns>
        public static bool operator !=(Planed a, Planed b)
        {
            return !(a == b);
        }
    }
}