FluidSim/Core/Solver.cs

using System;
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;

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

        /// <summary>
        /// Set boundary type for a pipe end. isA = true for port A (left), false for port B (right).
        /// </summary>
        public void SetPipeBoundary(Pipe1D pipe, bool isA, BoundaryType type, double ambientPressure = 101325.0)
        {
            if (isA)
            {
                pipe.SetABoundaryType(type);
                if (type == BoundaryType.OpenEnd)
                    pipe.SetAAmbientPressure(ambientPressure);
            }
            else
            {
                pipe.SetBBoundaryType(type);
                if (type == BoundaryType.OpenEnd)
                    pipe.SetBAmbientPressure(ambientPressure);
            }
        }

        public float Step()
        {
            // 1. Volumes publish state
            foreach (var v in _volumes)
                v.PushStateToPort();

            // 2. Set volume BCs for volume‑coupled ends
            foreach (var conn in _connections)
            {
                if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                {
                    var pipe = GetPipe(conn.PortA);
                    bool isA = pipe.PortA == conn.PortA;
                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                        SetVolumeBC(conn.PortA, conn.PortB);
                }
                else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                {
                    var pipe = GetPipe(conn.PortB);
                    bool isA = pipe.PortB == conn.PortB;
                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                        SetVolumeBC(conn.PortB, conn.PortA);
                }
            }

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

            for (int sub = 0; sub < nSub; sub++)
            {
                foreach (var p in _pipes)
                    p.SimulateSingleStep(dtSub);

                foreach (var conn in _connections)
                {
                    if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                    {
                        var pipe = GetPipe(conn.PortA);
                        bool isA = pipe.PortA == conn.PortA;
                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                            TransferAndIntegrate(conn.PortA, conn.PortB, dtSub);
                    }
                    else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                    {
                        var pipe = GetPipe(conn.PortB);
                        bool isA = pipe.PortB == conn.PortB;
                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                            TransferAndIntegrate(conn.PortB, conn.PortA, dtSub);
                    }
                }

                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 isA = pipe.PortA == conn.PortA;
                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                                SetVolumeBC(conn.PortA, conn.PortB);
                        }
                        else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                        {
                            var pipe = GetPipe(conn.PortB);
                            bool isA = pipe.PortB == conn.PortB;
                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                                SetVolumeBC(conn.PortB, conn.PortA);
                        }
                    }
                }
            }

            // 5. Audio samples (none for now, but placeholder)
            var audioSamples = new List<float>();
            foreach (var conn in _connections)
            {
                if (conn is SoundConnection sc)
                    audioSamples.Add(sc.GetAudioSample());
            }

            // 6. Clear 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 isA = pipe.PortA == pipePort;
            if (isA)
                pipe.SetAVolumeState(volPort.Density, volPort.Pressure);
            else
                pipe.SetBVolumeState(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 (from PushStateToPort) is used

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