using System;
using FluidSim.Components;

namespace FluidSim.Core
{
    public static class NozzleFlow
    {
        public static void Compute(Volume0D vol, double area, double downstreamPressure,
                                   out double massFlow, out double rhoFace, out double uFace, out double pFace,
                                   double gamma = 1.4)
        {
            // Default fallback (no flow)
            massFlow = 0.0;
            rhoFace = 0.0;
            uFace = 0.0;
            pFace = 0.0;

            if (vol == null || vol.Mass <= 0 || vol.Volume <= 0)
                return;

            double p0 = vol.Pressure;
            double T0 = vol.Temperature;
            double R = vol.GasConstant;
            double rho0 = vol.Density;

            if (double.IsNaN(p0) || double.IsNaN(T0) || double.IsNaN(rho0) ||
                p0 <= 0 || T0 <= 0 || rho0 <= 0)
                return;

            double pr = downstreamPressure / p0;
            double choked = Math.Pow(2.0 / (gamma + 1.0), gamma / (gamma - 1.0));
            if (pr < choked) pr = choked;

            double M = Math.Sqrt((2.0 / (gamma - 1.0)) * (Math.Pow(pr, -(gamma - 1.0) / gamma) - 1.0));
            if (double.IsNaN(M)) return;

            uFace = M * Math.Sqrt(gamma * R * T0);
            rhoFace = rho0 * Math.Pow(pr, 1.0 / gamma);
            pFace = p0 * pr;

            massFlow = rhoFace * uFace * area;
            if (double.IsNaN(massFlow) || double.IsInfinity(massFlow))
                massFlow = 0.0;
        }
    }
}