using System;
using FluidSim.Interfaces;

namespace FluidSim.Components
{
    public enum BoundaryType
    {
        VolumeCoupling,
        OpenEnd,
        ClosedEnd
    }

    public class Pipe1D
    {
        public Port PortA { get; }
        public Port PortB { get; }
        public double Area => _area;
        public double DampingMultiplier { get; set; } = 1.0;

        private int _n;
        private double _dx, _dt, _gamma, _area, _diameter;
        private double[] _rho, _rhou, _E;

        private double _rhoLeft, _pLeft;
        private double _rhoRight, _pRight;
        private bool _leftBCSet, _rightBCSet;

        private BoundaryType _leftBCType = BoundaryType.VolumeCoupling;
        private BoundaryType _rightBCType = BoundaryType.VolumeCoupling;

        private double _leftAmbientPressure = 101325.0;
        private double _rightAmbientPressure = 101325.0;

        private const double CflTarget = 0.8;
        private const double ReferenceSoundSpeed = 340.0;

        public int GetCellCount() => _n;
        public double GetCellDensity(int i) => _rho[i];
        public double GetCellPressure(int i) => Pressure(i);
        public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);

        public BoundaryType LeftBCType => _leftBCType;
        public BoundaryType RightBCType => _rightBCType;

        public Pipe1D(double length, double area, int sampleRate, int forcedCellCount = 0)
        {
            double dtGlobal = 1.0 / sampleRate;
            int nCells;

            if (forcedCellCount > 1)
            {
                nCells = forcedCellCount;
            }
            else
            {
                double dxTarget = ReferenceSoundSpeed * dtGlobal * CflTarget;
                nCells = Math.Max(2, (int)Math.Round(length / dxTarget, MidpointRounding.AwayFromZero));
                while (length / nCells > dxTarget * 1.01 && nCells < int.MaxValue - 1)
                    nCells++;
            }

            _n = nCells;
            _dx = length / _n;
            _dt = dtGlobal;
            _area = area;
            _gamma = 1.4;

            // Hydraulic diameter for a circular pipe
            _diameter = 2.0 * Math.Sqrt(area / Math.PI);

            _rho = new double[_n];
            _rhou = new double[_n];
            _E = new double[_n];

            PortA = new Port();
            PortB = new Port();
        }

        public void SetLeftBoundaryType(BoundaryType type) => _leftBCType = type;
        public void SetRightBoundaryType(BoundaryType type) => _rightBCType = type;
        public void SetLeftAmbientPressure(double p) => _leftAmbientPressure = p;
        public void SetRightAmbientPressure(double p) => _rightAmbientPressure = p;

        public void SetUniformState(double rho, double u, double p)
        {
            double e = p / ((_gamma - 1) * rho);
            double Etot = rho * e + 0.5 * rho * u * u;
            for (int i = 0; i < _n; i++)
            {
                _rho[i] = rho;
                _rhou[i] = rho * u;
                _E[i] = Etot;
            }
        }

        public void SetCellState(int i, double rho, double u, double p)
        {
            if (i < 0 || i >= _n) return;
            _rho[i] = rho;
            _rhou[i] = rho * u;
            double e = p / ((_gamma - 1) * rho);
            _E[i] = rho * e + 0.5 * rho * u * u;
        }

        public void SetLeftVolumeState(double rhoVol, double pVol)
        {
            _rhoLeft = rhoVol;
            _pLeft = pVol;
            _leftBCSet = true;
        }

        public void SetRightVolumeState(double rhoVol, double pVol)
        {
            _rhoRight = rhoVol;
            _pRight = pVol;
            _rightBCSet = true;
        }

        public void ClearBC() => _leftBCSet = _rightBCSet = false;

        public int GetRequiredSubSteps(double dtGlobal, double cflTarget = 0.8)
        {
            double maxW = 0.0;
            for (int i = 0; i < _n; i++)
            {
                double rho = _rho[i];
                double u = Math.Abs(_rhou[i] / Math.Max(rho, 1e-12));
                double c = Math.Sqrt(_gamma * Pressure(i) / Math.Max(rho, 1e-12));
                double local = u + c;
                if (local > maxW) maxW = local;
            }
            maxW = Math.Max(maxW, 1e-8);
            return Math.Max(1, (int)Math.Ceiling(dtGlobal * maxW / (cflTarget * _dx)));
        }

        public void SimulateSingleStep(double dtSub)
        {
            int n = _n;
            double[] Fm = new double[n + 1];
            double[] Fp = new double[n + 1];
            double[] Fe = new double[n + 1];

            // Left boundary (face 0)
            switch (_leftBCType)
            {
                case BoundaryType.VolumeCoupling:
                    if (_leftBCSet)
                    {
                        HLLCFlux(_rhoLeft, 0.0, _pLeft,
                                 _rho[0], _rhou[0] / Math.Max(_rho[0], 1e-12), Pressure(0),
                                 out Fm[0], out Fp[0], out Fe[0]);
                    }
                    else
                    {
                        Fm[0] = 0; Fp[0] = Pressure(0); Fe[0] = 0;
                    }
                    break;

                case BoundaryType.OpenEnd:
                    {
                        double rhoR = _rho[0];
                        double uR = _rhou[0] / Math.Max(rhoR, 1e-12);
                        double pR = Pressure(0);
                        HLLCFlux(rhoR, uR, _leftAmbientPressure,
                                 rhoR, uR, pR,
                                 out Fm[0], out Fp[0], out Fe[0]);
                    }
                    break;

                case BoundaryType.ClosedEnd:
                    {
                        double rhoR = _rho[0];
                        double uR = _rhou[0] / Math.Max(rhoR, 1e-12);
                        double pR = Pressure(0);
                        HLLCFlux(rhoR, -uR, pR,
                                 rhoR, uR, pR,
                                 out Fm[0], out Fp[0], out Fe[0]);
                    }
                    break;
            }

            // Internal faces
            for (int i = 0; i < n - 1; i++)
            {
                double uL = _rhou[i] / Math.Max(_rho[i], 1e-12);
                double uR = _rhou[i + 1] / Math.Max(_rho[i + 1], 1e-12);
                HLLCFlux(_rho[i], uL, Pressure(i),
                         _rho[i + 1], uR, Pressure(i + 1),
                         out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
            }

            // Right boundary (face n)
            switch (_rightBCType)
            {
                case BoundaryType.VolumeCoupling:
                    if (_rightBCSet)
                    {
                        double rhoL = _rho[n - 1];
                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
                        double pL = Pressure(n - 1);
                        HLLCFlux(rhoL, uL, pL,
                                 _rhoRight, 0.0, _pRight,
                                 out Fm[n], out Fp[n], out Fe[n]);
                    }
                    else
                    {
                        Fm[n] = 0; Fp[n] = Pressure(n - 1); Fe[n] = 0;
                    }
                    break;

                case BoundaryType.OpenEnd:
                    {
                        double rhoL = _rho[n - 1];
                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
                        double pL = Pressure(n - 1);
                        HLLCFlux(rhoL, uL, pL,
                                 rhoL, uL, _rightAmbientPressure,
                                 out Fm[n], out Fp[n], out Fe[n]);
                    }
                    break;

                case BoundaryType.ClosedEnd:
                    {
                        double rhoL = _rho[n - 1];
                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
                        double pL = Pressure(n - 1);
                        HLLCFlux(rhoL, uL, pL,
                                 rhoL, -uL, pL,
                                 out Fm[n], out Fp[n], out Fe[n]);
                    }
                    break;
            }

            // ---- Cell update with linear laminar damping ----
            double radius = _diameter / 2.0;
            double mu_air = 1.8e-5;                       // dynamic viscosity of air (Pa·s)
            double laminarCoeff = DampingMultiplier * 8.0 * mu_air / (radius * radius);

            for (int i = 0; i < n; i++)
            {
                // Flux divergence
                double dM = (Fm[i + 1] - Fm[i]) / _dx;
                double dP = (Fp[i + 1] - Fp[i]) / _dx;
                double dE = (Fe[i + 1] - Fe[i]) / _dx;

                _rho[i] -= dtSub * dM;
                _rhou[i] -= dtSub * dP;
                _E[i] -= dtSub * dE;

                // Laminar viscous damping on momentum (implicit exponential decay)
                double rho = Math.Max(_rho[i], 1e-12);
                double dampingRate = laminarCoeff / rho;   // 1/s
                double dampingFactor = Math.Exp(-dampingRate * dtSub);
                _rhou[i] *= dampingFactor;
                // Note: total energy _E[i] is unchanged – kinetic energy loss becomes internal heat

                // Physical bounds
                if (_rho[i] < 1e-12) _rho[i] = 1e-12;
                double kinetic = 0.5 * _rhou[i] * _rhou[i] / _rho[i];
                double pMin = 100.0;
                double eMin = pMin / ((_gamma - 1) * _rho[i]) + kinetic;
                if (_E[i] < eMin) _E[i] = eMin;
            }

            // Port quantities (only meaningful for volume‑coupled ends)
            double mdotA_sub = _leftBCType == BoundaryType.VolumeCoupling && _leftBCSet ? Fm[0] * _area : 0.0;
            double mdotB_sub = _rightBCType == BoundaryType.VolumeCoupling && _rightBCSet ? -Fm[n] * _area : 0.0;

            PortA.MassFlowRate = mdotA_sub;
            PortB.MassFlowRate = mdotB_sub;
            PortA.Pressure = Pressure(0);
            PortB.Pressure = Pressure(_n - 1);
            PortA.Density = _rho[0];
            PortB.Density = _rho[_n - 1];

            if (_leftBCType == BoundaryType.VolumeCoupling && _leftBCSet)
            {
                PortA.SpecificEnthalpy = mdotA_sub < 0
                    ? GetCellTotalSpecificEnthalpy(0)
                    : 0.0;
            }
            if (_rightBCType == BoundaryType.VolumeCoupling && _rightBCSet)
            {
                PortB.SpecificEnthalpy = mdotB_sub < 0
                    ? GetCellTotalSpecificEnthalpy(_n - 1)
                    : 0.0;
            }
        }

        private double GetCellTotalSpecificEnthalpy(int i)
        {
            double rho = Math.Max(_rho[i], 1e-12);
            double u = _rhou[i] / rho;
            double p = Pressure(i);
            double h = _gamma / (_gamma - 1.0) * p / rho;
            return h + 0.5 * u * u;
        }

        private double Pressure(int i) =>
            (_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / Math.Max(_rho[i], 1e-12));

        private void HLLCFlux(double rL, double uL, double pL,
                              double rR, double uR, double pR,
                              out double fm, out double fp, out double fe)
        {
            double cL = Math.Sqrt(_gamma * pL / Math.Max(rL, 1e-12));
            double cR = Math.Sqrt(_gamma * pR / Math.Max(rR, 1e-12));
            double EL = pL / ((_gamma - 1) * rL) + 0.5 * uL * uL;
            double ER = pR / ((_gamma - 1) * rR) + 0.5 * uR * uR;
            double SL = Math.Min(uL - cL, uR - cR);
            double SR = Math.Max(uL + cL, uR + cR);

            double Ss = (pR - pL + rL * uL * (SL - uL) - rR * uR * (SR - uR))
                      / (rL * (SL - uL) - rR * (SR - uR));

            double FrL_m = rL * uL, FrL_p = rL * uL * uL + pL, FrL_e = (rL * EL + pL) * uL;
            double FrR_m = rR * uR, FrR_p = rR * uR * uR + pR, FrR_e = (rR * ER + pR) * uR;

            if (SL >= 0) { fm = FrL_m; fp = FrL_p; fe = FrL_e; }
            else if (SR <= 0) { fm = FrR_m; fp = FrR_p; fe = FrR_e; }
            else if (Ss >= 0)
            {
                double rsL = rL * (SL - uL) / (SL - Ss);
                double ps = pL + rL * (SL - uL) * (Ss - uL);
                double EsL = EL + (Ss - uL) * (Ss + pL / (rL * (SL - uL)));
                fm = rsL * Ss; fp = rsL * Ss * Ss + ps; fe = (rsL * EsL + ps) * Ss;
            }
            else
            {
                double rsR = rR * (SR - uR) / (SR - Ss);
                double ps = pL + rL * (SL - uL) * (Ss - uL);
                double EsR = ER + (Ss - uR) * (Ss + pR / (rR * (SR - uR)));
                fm = rsR * Ss; fp = rsR * Ss * Ss + ps; fe = (rsR * EsR + ps) * Ss;
            }
        }

        public double GetPressureAtFraction(double fraction)
        {
            int i = (int)(fraction * (_n - 1));
            i = Math.Clamp(i, 0, _n - 1);
            return Pressure(i);
        }
    }
}