using System;
using System.Diagnostics;
using FluidSim.Interfaces;

namespace FluidSim.Components
{
    /// <summary>
    /// 1‑D compressible Euler pipe with Lax‑Friedrichs finite‑volume scheme.
    /// Ghost states are set externally via SetGhostLeft/Right; they are always required.
    /// Now includes a passive scalar for air mass fraction.
    /// </summary>
    public class Pipe1D : IComponent
    {
        public const bool EnableDetailedProfiling = false;   // set to false in release builds

        public Port PortA { get; }
        public Port PortB { get; }
        public double Area { get; }
        public double DampingMultiplier { get; set; } = 10.0;
        public double EnergyRelaxationRate { get; set; } = 5.0;   // 1/s

        private double _ambientPressure = 101325.0;
        public double AmbientPressure
        {
            get => _ambientPressure;
            set
            {
                _ambientPressure = value;
                _ambientEnergyReference = value / (_gamma - 1.0);
            }
        }

        private readonly int _n;
        private readonly double _dx;
        private readonly double _diameter;
        private readonly double _gamma = 1.4;

        private double[] _rho, _rhou, _E;
        private double[] _Y;               // air mass fraction
        private double[] _fluxM, _fluxP, _fluxE;

        private double _rhoGhostL, _uGhostL, _pGhostL, _YGhostL;
        private double _rhoGhostR, _uGhostR, _pGhostR, _YGhostR;
        private bool _ghostLValid, _ghostRValid;

        private double _laminarCoeff;
        private double _ambientEnergyReference;

        // ---------- Profiling accumulators ----------
        private long _profPrecomputeTicks;
        private long _profLeftFluxTicks;
        private long _profInteriorLoopTicks;
        private long _profRightFluxTicks;
        private long _profPortUpdateTicks;
        private long _profCallCount;

        public Pipe1D(double length, double area, int cellCount)
        {
            if (cellCount < 4) throw new ArgumentException("cellCount must be at least 4");

            _n = cellCount;
            _dx = length / _n;
            Area = area;
            _diameter = 2.0 * Math.Sqrt(area / Math.PI);

            _rho = new double[_n];
            _rhou = new double[_n];
            _E = new double[_n];
            _Y = new double[_n];
            _fluxM = new double[_n + 1];
            _fluxP = new double[_n + 1];
            _fluxE = new double[_n + 1];

            double mu_air = 1.8e-5;
            double radius = _diameter * 0.5;
            _laminarCoeff = 8.0 * mu_air / (radius * radius);

            _ambientEnergyReference = 101325.0 / (_gamma - 1.0);

            PortA = new Port { Owner = this };
            PortB = new Port { Owner = this };

            SetUniformState(1.225, 0.0, 101325.0);
        }

        IReadOnlyList<Port> IComponent.Ports => new[] { PortA, PortB };

        public void UpdateState(double dt) { }

        // ---------- Ghost interface ----------
        public void SetGhostLeft(double rho, double u, double p, double airFraction)
        {
            _rhoGhostL = rho; _uGhostL = u; _pGhostL = p; _YGhostL = airFraction; _ghostLValid = true;
        }
        public void SetGhostRight(double rho, double u, double p, double airFraction)
        {
            _rhoGhostR = rho; _uGhostR = u; _pGhostR = p; _YGhostR = airFraction; _ghostRValid = true;
        }
        public void ClearGhostFlags() { _ghostLValid = false; _ghostRValid = false; }

        public double GetInteriorAirFractionLeft() => _Y[0];
        public double GetInteriorAirFractionRight() => _Y[_n - 1];

        public (double rho, double u, double p) GetInteriorStateLeft()
        {
            double rho = Math.Max(_rho[0], 1e-12);
            double u = _rhou[0] / rho;
            double p = PressureScalar(0);
            return (rho, u, p);
        }
        public (double rho, double u, double p) GetInteriorStateRight()
        {
            double rho = Math.Max(_rho[_n - 1], 1e-12);
            double u = _rhou[_n - 1] / rho;
            double p = PressureScalar(_n - 1);
            return (rho, u, p);
        }
        public int CellCount => _n;
        public double GetCellDensity(int i) => _rho[i];
        public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);
        public double GetCellPressure(int i) => PressureScalar(i);

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

        // ---------- Main step (per sub‑step) ----------
        public void SimulateSingleStep(double dtSub)
        {
            if (!_ghostLValid || !_ghostRValid)
                throw new InvalidOperationException("Ghost cells not set before SimulateSingleStep.");

            double dt = dtSub;
            int n = _n;
            double dt_dx = dt / _dx;
            double coeff = _laminarCoeff * DampingMultiplier;
            double relaxRate = EnergyRelaxationRate;
            double gamma = _gamma;
            double gm1 = gamma - 1.0;

            // ---------- Profiling start ----------
            long t0 = 0, t1 = 0;
            if (EnableDetailedProfiling)
            {
                t0 = Stopwatch.GetTimestamp();
                _profCallCount++;
            }

            // ---------- Phase 1: Pre‑compute pressure and speed of sound ----------
            double[] p = new double[n];
            double[] c = new double[n];
            for (int i = 0; i < n; i++)
            {
                double rho = Math.Max(_rho[i], 1e-12);
                double u = _rhou[i] / rho;
                p[i] = gm1 * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / rho);
                c[i] = Math.Sqrt(gamma * p[i] / rho);
            }

            if (EnableDetailedProfiling)
            {
                t1 = Stopwatch.GetTimestamp();
                _profPrecomputeTicks += (t1 - t0);
                t0 = t1;
            }

            // ---------- Local flux functions ----------
            void LaxFlux(double rL, double uL, double pL, double cL,
                         double rR, double uR, double pR, double cR,
                         out double fm, out double fp, out double fe)
            {
                double EL = pL / (gm1 * rL) + 0.5 * uL * uL;
                double ER = pR / (gm1 * rR) + 0.5 * uR * uR;
                double Fm_L = rL * uL;
                double Fp_L = rL * uL * uL + pL;
                double Fe_L = (rL * EL + pL) * uL;
                double Fm_R = rR * uR;
                double Fp_R = rR * uR * uR + pR;
                double Fe_R = (rR * ER + pR) * uR;
                double alpha = Math.Max(Math.Abs(uL) + cL, Math.Abs(uR) + cR);
                fm = 0.5 * (Fm_L + Fm_R) - 0.5 * alpha * (rR - rL);
                fp = 0.5 * (Fp_L + Fp_R) - 0.5 * alpha * (rR * uR - rL * uL);
                fe = 0.5 * (Fe_L + Fe_R) - 0.5 * alpha * (rR * ER - rL * EL);
            }

            void ScalarFlux(double rL, double uL, double cL, double YL,
                            double rR, double uR, double cR, double YR,
                            double alpha, out double fy)
            {
                double Fm_L = rL * uL;
                double Fm_R = rR * uR;
                fy = 0.5 * (Fm_L * YL + Fm_R * YR) - 0.5 * alpha * (rR * YR - rL * YL);
            }

            // ---------- Phase 2: Left face flux (ghostL – cell 0) ----------
            double rL_ghost = Math.Max(_rhoGhostL, 1e-12);
            double pL_ghost = _pGhostL;
            double uL_ghost = _uGhostL;
            double cL_ghost = Math.Sqrt(gamma * pL_ghost / rL_ghost);

            LaxFlux(rL_ghost, uL_ghost, pL_ghost, cL_ghost,
                    _rho[0], _rhou[0] / Math.Max(_rho[0], 1e-12), p[0], c[0],
                    out double fluxM_left, out double fluxP_left, out double fluxE_left);

            double alphaLeft = Math.Max(Math.Abs(uL_ghost) + cL_ghost,
                                        Math.Abs(_rhou[0] / Math.Max(_rho[0], 1e-12)) + c[0]);
            ScalarFlux(rL_ghost, uL_ghost, cL_ghost, _YGhostL,
                   _rho[0], _rhou[0] / Math.Max(_rho[0], 1e-12), c[0], _Y[0],
                   alphaLeft, out double fluxY_left);

            if (EnableDetailedProfiling)
            {
                t1 = Stopwatch.GetTimestamp();
                _profLeftFluxTicks += (t1 - t0);
                t0 = t1;
            }

            // ---------- Phase 3: Interior loop (fluxes + cell updates) ----------
            double fluxM_prev = fluxM_left;
            double fluxP_prev = fluxP_left;
            double fluxE_prev = fluxE_left;
            double fluxY_prev = fluxY_left;

            for (int i = 0; i < n - 1; i++)
            {
                int iL = i;
                int iR = i + 1;

                double rL = Math.Max(_rho[iL], 1e-12);
                double uL = _rhou[iL] / rL;
                double pL = p[iL];
                double cL = c[iL];
                double YL = _Y[iL];

                double rR = Math.Max(_rho[iR], 1e-12);
                double uR = _rhou[iR] / rR;
                double pR = p[iR];
                double cR = c[iR];
                double YR = _Y[iR];

                LaxFlux(rL, uL, pL, cL, rR, uR, pR, cR,
                        out double fluxM_right, out double fluxP_right, out double fluxE_right);

                double alpha = Math.Max(Math.Abs(uL) + cL, Math.Abs(uR) + cR);
                ScalarFlux(rL, uL, cL, YL, rR, uR, cR, YR, alpha, out double fluxY_right);

                // Update cell i
                double r = _rho[i];
                double ru = _rhou[i];
                double E = _E[i];
                double Y = _Y[i];

                double newR = r - dt_dx * (fluxM_right - fluxM_prev);
                double newRu = ru - dt_dx * (fluxP_right - fluxP_prev);
                double newE = E - dt_dx * (fluxE_right - fluxE_prev);
                double oldRhoY = r * Y;
                double newRhoY = oldRhoY - dt_dx * (fluxY_right - fluxY_prev);

                double dampingFactor = Math.Exp(-coeff / Math.Max(r, 1e-12) * dt);
                newRu *= dampingFactor;
                double relaxFactor = Math.Exp(-relaxRate * dt);
                newE = _ambientEnergyReference + (newE - _ambientEnergyReference) * relaxFactor;

                newR = Math.Max(newR, 1e-12);
                double kin = 0.5 * newRu * newRu / Math.Max(newR, 1e-12);
                double eMin = 100.0 / gm1 + kin;
                newE = Math.Max(newE, eMin);

                _rho[i] = newR;
                _rhou[i] = newRu;
                _E[i] = newE;
                _Y[i] = Math.Clamp(newRhoY / newR, 0.0, 1.0);

                fluxM_prev = fluxM_right;
                fluxP_prev = fluxP_right;
                fluxE_prev = fluxE_right;
                fluxY_prev = fluxY_right;
            }

            if (EnableDetailedProfiling)
            {
                t1 = Stopwatch.GetTimestamp();
                _profInteriorLoopTicks += (t1 - t0);
                t0 = t1;
            }

            // ---------- Phase 4: Right face flux (cell n‑1 – ghostR) ----------
            double rR_ghost = Math.Max(_rhoGhostR, 1e-12);
            double pR_ghost = _pGhostR;
            double uR_ghost = _uGhostR;
            double cR_ghost = Math.Sqrt(gamma * pR_ghost / rR_ghost);

            double rInt = _rho[n - 1];
            double uInt = _rhou[n - 1] / Math.Max(rInt, 1e-12);

            LaxFlux(rInt, uInt, p[n - 1], c[n - 1],
                    rR_ghost, uR_ghost, pR_ghost, cR_ghost,
                    out double fluxM_right_final, out double fluxP_right_final, out double fluxE_right_final);

            double alphaRight = Math.Max(Math.Abs(uInt) + c[n - 1], Math.Abs(uR_ghost) + cR_ghost);
            ScalarFlux(rInt, uInt, c[n - 1], _Y[n - 1],
                       rR_ghost, uR_ghost, cR_ghost, _YGhostR,
                       alphaRight, out double fluxY_right_final);

            // Update last cell
            {
                int i = n - 1;
                double r = _rho[i];
                double ru = _rhou[i];
                double E = _E[i];
                double Y = _Y[i];

                double newR = r - dt_dx * (fluxM_right_final - fluxM_prev);
                double newRu = ru - dt_dx * (fluxP_right_final - fluxP_prev);
                double newE = E - dt_dx * (fluxE_right_final - fluxE_prev);
                double oldRhoY = r * Y;
                double newRhoY = oldRhoY - dt_dx * (fluxY_right_final - fluxY_prev);

                double dampingFactor = Math.Exp(-coeff / Math.Max(r, 1e-12) * dt);
                newRu *= dampingFactor;
                double relaxFactor = Math.Exp(-relaxRate * dt);
                newE = _ambientEnergyReference + (newE - _ambientEnergyReference) * relaxFactor;

                newR = Math.Max(newR, 1e-12);
                double kin = 0.5 * newRu * newRu / Math.Max(newR, 1e-12);
                double eMin = 100.0 / gm1 + kin;
                newE = Math.Max(newE, eMin);

                _rho[i] = newR;
                _rhou[i] = newRu;
                _E[i] = newE;
                _Y[i] = Math.Clamp(newRhoY / newR, 0.0, 1.0);
            }

            if (EnableDetailedProfiling)
            {
                t1 = Stopwatch.GetTimestamp();
                _profRightFluxTicks += (t1 - t0);
                t0 = t1;
            }

            // ---------- Phase 5: Update port states ----------
            (double rhoA, double uA, double pA) = GetInteriorStateLeft();
            PortA.Pressure = pA; PortA.Density = rhoA;
            PortA.Temperature = pA / (rhoA * 287.0);
            PortA.SpecificEnthalpy = gm1 / (gamma - 1.0) * pA / rhoA;
            PortA.AirFraction = _Y[0];

            (double rhoB, double uB, double pB) = GetInteriorStateRight();
            PortB.Pressure = pB; PortB.Density = rhoB;
            PortB.Temperature = pB / (rhoB * 287.0);
            PortB.SpecificEnthalpy = gm1 / (gamma - 1.0) * pB / rhoB;
            PortB.AirFraction = _Y[_n - 1];

            if (EnableDetailedProfiling)
            {
                t1 = Stopwatch.GetTimestamp();
                _profPortUpdateTicks += (t1 - t0);
            }
        }

        private double PressureScalar(int i)
        {
            double rho = Math.Max(_rho[i], 1e-12);
            return (_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / rho);
        }

        public void SetUniformState(double rho, double u, double p)
        {
            double e = p / ((_gamma - 1.0) * rho);
            double E = rho * e + 0.5 * rho * u * u;
            for (int i = 0; i < _n; i++)
            {
                _rho[i] = rho;
                _rhou[i] = rho * u;
                _E[i] = E;
                _Y[i] = 1.0;   // initially pure air
            }
        }

        public void SetCellState(int i, double rho, double u, double p)
        {
            if (i < 0 || i >= _n) return;
            double e = p / ((_gamma - 1.0) * rho);
            double E = rho * e + 0.5 * rho * u * u;
            _rho[i] = rho;
            _rhou[i] = rho * u;
            _E[i] = E;
            _Y[i] = 1.0;
        }

        public void SetCellPressure(int i, double p)
        {
            if (i < 0 || i >= _n) return;
            double rho = _rho[i];
            double u = _rhou[i] / rho;
            double e = p / ((_gamma - 1.0) * rho);
            _E[i] = rho * e + 0.5 * rho * u * u;
        }

        // ---------- Public profiling interface ----------
        public void ResetDetailCounters()
        {
            _profPrecomputeTicks = 0;
            _profLeftFluxTicks = 0;
            _profInteriorLoopTicks = 0;
            _profRightFluxTicks = 0;
            _profPortUpdateTicks = 0;
            _profCallCount = 0;
        }

        public string GetDetailProfileReport()
        {
            if (!EnableDetailedProfiling)
                return "Detailed profiling disabled.";

            double freq = Stopwatch.Frequency;
            long totalTicks = _profPrecomputeTicks + _profLeftFluxTicks +
                              _profInteriorLoopTicks + _profRightFluxTicks +
                              _profPortUpdateTicks;

            if (totalTicks == 0) return "No profiling data.";

            double totalSec = totalTicks / freq;
            double avgCallSec = totalSec / _profCallCount;
            double avgCallUs = avgCallSec * 1e6;

            string report = $"  Pipe detailed (over {_profCallCount} calls, total {totalSec * 1000:F2} ms):\n";
            report += $"    Avg per call: {avgCallUs:F2} µs\n";
            report += $"    Precompute p,c:   {_profPrecomputeTicks * 100.0 / totalTicks:F1} %  ({_profPrecomputeTicks / freq * 1e6 / _profCallCount:F2} µs/call)\n";
            report += $"    Left face flux:   {_profLeftFluxTicks * 100.0 / totalTicks:F1} %  ({_profLeftFluxTicks / freq * 1e6 / _profCallCount:F2} µs/call)\n";
            report += $"    Interior loop:    {_profInteriorLoopTicks * 100.0 / totalTicks:F1} %  ({_profInteriorLoopTicks / freq * 1e6 / _profCallCount:F2} µs/call)\n";
            report += $"    Right face flux:  {_profRightFluxTicks * 100.0 / totalTicks:F1} %  ({_profRightFluxTicks / freq * 1e6 / _profCallCount:F2} µs/call)\n";
            report += $"    Port update:      {_profPortUpdateTicks * 100.0 / totalTicks:F1} %  ({_profPortUpdateTicks / freq * 1e6 / _profCallCount:F2} µs/call)\n";
            return report;
        }
    }
}