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

namespace FluidSim.Components
{
    /// <summary>
    /// Zero‑dimensional control volume with arbitrary number of ports.
    /// Integrates mass and energy fluxes from all ports.
    /// Safeguards keep a tiny amount of gas to avoid negative states.
    /// </summary>
    public class Volume0D : IComponent
    {
        public List<Port> Ports { get; } = new List<Port>();

        public double Mass { get; private set; }
        public double InternalEnergy { get; private set; }
        public double Volume { get; set; }
        public double Dvdt { get; set; }
        public double Gamma { get; set; } = 1.4;
        public double GasConstant { get; set; } = 287.0;

        // Ambient pressure used for emergency refill – default 101325 Pa
        public double AmbientPressure { get; set; } = 101325.0;

        // Derived quantities
        public double Density => Mass / Math.Max(Volume, 1e-12);
        public double Pressure => (Gamma - 1.0) * InternalEnergy / Math.Max(Volume, 1e-12);
        public double Temperature => Pressure / Math.Max(Density * GasConstant, 1e-12);
        public double SpecificEnthalpy => Gamma / (Gamma - 1.0) * Pressure / Math.Max(Density, 1e-12);

        public Volume0D(double initialVolume, double initialPressure,
                        double initialTemperature, double gasConstant = 287.0, double gamma = 1.4)
        {
            GasConstant = gasConstant;
            Gamma = gamma;
            Volume = initialVolume;
            Dvdt = 0.0;

            double rho0 = initialPressure / (GasConstant * initialTemperature);
            Mass = rho0 * Volume;
            InternalEnergy = (initialPressure * Volume) / (Gamma - 1.0);
        }

        /// <summary>Add a new port and initialise it to the volume's current state.</summary>
        public Port CreatePort()
        {
            var port = new Port { Owner = this };
            // Set the port state immediately to avoid a mismatch before the first integration
            port.Pressure = Pressure;
            port.Density = Density;
            port.Temperature = Temperature;
            port.SpecificEnthalpy = SpecificEnthalpy;
            Ports.Add(port);
            return port;
        }

        /// <summary>
        /// Integrate over dt using the MassFlowRate and SpecificEnthalpy
        /// that have been set on each port during the coupling resolution phase.
        /// </summary>
        public void UpdateState(double dt)
        {
            double totalMdot = 0.0;
            double totalEdot = 0.0;

            foreach (var port in Ports)
            {
                totalMdot += port.MassFlowRate;
                // mdot * h gives energy flow: positive mdot = inflow, negative = outflow
                totalEdot += port.MassFlowRate * port.SpecificEnthalpy;
            }

            double dm = totalMdot * dt;
            double dE = totalEdot * dt - Pressure * Dvdt * dt;   // piston work

            Mass += dm;
            InternalEnergy += dE;

            // Safeguards: keep at least 1 µg of gas at a small pressure
            double V = Math.Max(Volume, 1e-12);
            if (Mass < 1e-9)
            {
                Mass = 1e-9;
                InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
            }
            else if (InternalEnergy < 0.0)
            {
                InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
            }

            // Final non‑negative clamps (should not be needed after above)
            if (Mass < 0.0) Mass = 1e-9;
            if (InternalEnergy < 0.0) InternalEnergy = AmbientPressure * V / (Gamma - 1.0);

            // Push updated state back to all ports
            double p = Pressure, rho = Density, T = Temperature, h = SpecificEnthalpy;
            foreach (var port in Ports)
            {
                port.Pressure = p;
                port.Density = rho;
                port.Temperature = T;
                port.SpecificEnthalpy = h;   // will be overwritten by couplings for inflow, but this is the default
            }
        }

        IReadOnlyList<Port> IComponent.Ports => Ports;
    }
}