using System;
using FluidSim.Interfaces;

namespace FluidSim.Components
{
    public class Orifice
    {
        public Port PortA { get; }
        public Port PortB { get; }

        public double Area { get; set; }
        public double DischargeCoeff { get; set; } = 0.62;
        public double Gamma { get; set; } = 1.4;

        public Orifice(double area)
        {
            Area = area;
            PortA = new Port();
            PortB = new Port();
        }

        public void Simulate()
        {
            double pA = PortA.Pressure, pB = PortB.Pressure;
            double dp = pA - pB;
            double rho = dp >= 0 ? PortA.Density : PortB.Density;
            if (rho <= 0) rho = 1.225;

            double massFlow;
            double absDp = Math.Abs(dp);
            double critical = 1e-3 * pA;   // blend threshold

            if (absDp < critical)
            {
                // Linearised region for numerical stability
                massFlow = Area * DischargeCoeff * Math.Sqrt(2 * rho * critical) * dp / critical;
            }
            else
            {
                double sign = Math.Sign(dp);
                double pratio = Math.Min(pA, pB) / Math.Max(pA, pB);
                double choked = Math.Pow(2.0 / (Gamma + 1.0), Gamma / (Gamma - 1.0));

                if (pratio < choked)
                {
                    double term = Math.Sqrt(Gamma * Math.Pow(2.0 / (Gamma + 1.0), (Gamma + 1.0) / (Gamma - 1.0)));
                    massFlow = DischargeCoeff * Area * Math.Sqrt(rho * Math.Max(pA, pB)) * term;
                }
                else
                {
                    double exp = 1.0 - Math.Pow(pratio, (Gamma - 1.0) / Gamma);
                    massFlow = DischargeCoeff * Area *
                        Math.Sqrt(2.0 * rho * Math.Max(pA, pB) * (Gamma / (Gamma - 1.0)) * pratio * pratio * exp);
                }
                massFlow *= sign;
            }

            PortA.MassFlowRate = -massFlow;   // outflow from A
            PortB.MassFlowRate = massFlow;    // inflow to B

            if (massFlow > 0) // A->B
            {
                PortA.SpecificEnthalpy = PortA.SpecificEnthalpy;
                PortB.SpecificEnthalpy = PortA.SpecificEnthalpy;
            }
            else
            {
                PortA.SpecificEnthalpy = PortB.SpecificEnthalpy;
                PortB.SpecificEnthalpy = PortB.SpecificEnthalpy;
            }
        }
    }
}