FluidSim/Core/Solver.cs

using System.Collections.Generic;
using FluidSim.Components;
using FluidSim.Interfaces;

namespace FluidSim.Core
{
    public class Solver
    {
        private readonly List<Volume0D> _volumes = new();
        private readonly List<Pipe1D> _pipes = new();
        private readonly List<Connection> _connections = new();

        private double _dt;   // global time step

        public void AddVolume(Volume0D v) => _volumes.Add(v);
        public void AddPipe(Pipe1D p) => _pipes.Add(p);
        public void AddConnection(Connection c) => _connections.Add(c);

        /// <summary>Set the global time step (called from Simulation).</summary>
        public void SetTimeStep(double dt) => _dt = dt;

        /// <summary>
        /// Convenient method to set the boundary type of a pipe end.
        /// </summary>
        public void SetPipeBoundary(Pipe1D pipe, bool isLeft, BoundaryType type, double ambientPressure = 101325.0)
        {
            if (isLeft)
            {
                pipe.SetLeftBoundaryType(type);
                if (type == BoundaryType.OpenEnd)
                    pipe.SetLeftAmbientPressure(ambientPressure);
            }
            else
            {
                pipe.SetRightBoundaryType(type);
                if (type == BoundaryType.OpenEnd)
                    pipe.SetRightAmbientPressure(ambientPressure);
            }
        }

        public float Step()
        {
            // 1. Volumes publish state to ports (only needed if any volume exists)
            foreach (var v in _volumes)
                v.PushStateToPort();

            // 2. Set initial pipe boundary conditions ONLY for volume‑coupled ends
            foreach (var conn in _connections)
            {
                if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                {
                    var pipe = GetPipe(conn.PortA);
                    bool isLeft = pipe.PortA == conn.PortA;
                    BoundaryType bc = isLeft ? pipe.LeftBCType : pipe.RightBCType;
                    if (bc == BoundaryType.VolumeCoupling)
                        SetVolumeBC(conn.PortA, conn.PortB);
                }
                else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                {
                    var pipe = GetPipe(conn.PortB);
                    bool isLeft = pipe.PortB == conn.PortB;
                    BoundaryType bc = isLeft ? pipe.LeftBCType : pipe.RightBCType;
                    if (bc == BoundaryType.VolumeCoupling)
                        SetVolumeBC(conn.PortB, conn.PortA);
                }
            }

            // 3. Determine number of sub‑steps
            int nSub = 1;
            foreach (var p in _pipes)
                nSub = Math.Max(nSub, p.GetRequiredSubSteps(_dt));
            double dtSub = _dt / nSub;

            // 4. Sub‑step loop
            for (int sub = 0; sub < nSub; sub++)
            {
                foreach (var p in _pipes)
                    p.SimulateSingleStep(dtSub);

                // Transfer flows only for volume‑coupled connections
                foreach (var conn in _connections)
                {
                    if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                    {
                        var pipe = GetPipe(conn.PortA);
                        bool isLeft = pipe.PortA == conn.PortA;
                        if (pipe.LeftBCType == BoundaryType.VolumeCoupling || pipe.RightBCType == BoundaryType.VolumeCoupling)
                            TransferAndIntegrate(conn.PortA, conn.PortB, dtSub);
                    }
                    else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                    {
                        var pipe = GetPipe(conn.PortB);
                        bool isLeft = pipe.PortB == conn.PortB;
                        if (pipe.LeftBCType == BoundaryType.VolumeCoupling || pipe.RightBCType == BoundaryType.VolumeCoupling)
                            TransferAndIntegrate(conn.PortB, conn.PortA, dtSub);
                    }
                }

                // Update BCs for volume‑coupled ends between sub‑steps
                if (sub < nSub - 1)
                {
                    foreach (var v in _volumes)
                        v.PushStateToPort();

                    foreach (var conn in _connections)
                    {
                        if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                        {
                            var pipe = GetPipe(conn.PortA);
                            bool isLeft = pipe.PortA == conn.PortA;
                            if ((isLeft && pipe.LeftBCType == BoundaryType.VolumeCoupling) ||
                                (!isLeft && pipe.RightBCType == BoundaryType.VolumeCoupling))
                                SetVolumeBC(conn.PortA, conn.PortB);
                        }
                        else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                        {
                            var pipe = GetPipe(conn.PortB);
                            bool isLeft = pipe.PortB == conn.PortB;
                            if ((isLeft && pipe.LeftBCType == BoundaryType.VolumeCoupling) ||
                                (!isLeft && pipe.RightBCType == BoundaryType.VolumeCoupling))
                                SetVolumeBC(conn.PortB, conn.PortA);
                        }
                    }
                }
            }

            // 5. Audio samples from SoundConnections (if any)
            var audioSamples = new List<float>();
            foreach (var conn in _connections)
            {
                if (conn is SoundConnection sc)
                    audioSamples.Add(sc.GetAudioSample());
            }

            // 6. Clear volume BC flags
            foreach (var p in _pipes)
                p.ClearBC();

            return SoundProcessor.MixAndClip(audioSamples.ToArray());
        }

        private bool IsVolumePort(Port p) => _volumes.Exists(v => v.Port == p);
        private bool IsPipePort(Port p) => _pipes.Exists(pp => pp.PortA == p || pp.PortB == p);
        private Pipe1D GetPipe(Port p) => _pipes.Find(pp => pp.PortA == p || pp.PortB == p);
        private Volume0D GetVolume(Port p) => _volumes.Find(v => v.Port == p);

        private void SetVolumeBC(Port pipePort, Port volPort)
        {
            var pipe = GetPipe(pipePort);
            if (pipe == null) return;
            bool isLeft = pipe.PortA == pipePort;
            if (isLeft)
                pipe.SetLeftVolumeState(volPort.Density, volPort.Pressure);
            else
                pipe.SetRightVolumeState(volPort.Density, volPort.Pressure);
        }

        private void TransferAndIntegrate(Port pipePort, Port volPort, double dtSub)
        {
            double mdot = pipePort.MassFlowRate;
            volPort.MassFlowRate = -mdot;

            if (mdot < 0)  // pipe → volume
            {
                volPort.SpecificEnthalpy = pipePort.SpecificEnthalpy;
            }
            // else: volume’s own enthalpy (set by PushStateToPort) is used

            GetVolume(volPort)?.Integrate(dtSub);
        }
    }
}