using System;
using FluidSim.Core;

namespace FluidSim.Core
{
    public class SoundProcessor
    {
        private readonly double dt;
        private readonly double scaleFactor;  // 1 / (4π r)
        private double prevMassFlowOut;
        private double smoothDMdt;
        private readonly double alpha;

        // New: low‑pass the mass flow signal before derivative
        private double flowLP;
        private readonly double lpAlpha;

        public float Gain { get; set; } = 1.0f;

        public SoundProcessor(int sampleRate, double listenerDistanceMeters = 1.0)
        {
            dt = 1.0 / sampleRate;
            scaleFactor = 1.0 / (4.0 * Math.PI * listenerDistanceMeters);

            // Smoothing time constant for the derivative: 10 ms (much smoother)
            double tau = 0.005;   // 10 ms
            alpha = Math.Exp(-dt / tau);

            // Low‑pass time constant for the mass flow: 5 ms (kneecap high‑freq directly)
            double tauLP = 0.005;
            lpAlpha = Math.Exp(-dt / tauLP);
        }

        public float Process(OpenEndLink openEnd)
        {
            double flowOut = openEnd.LastMassFlowRate;

            // Low‑pass the mass flow signal
            flowLP = lpAlpha * flowLP + (1.0 - lpAlpha) * flowOut;

            // Derivative of the smoothed mass flow
            double rawDerivative = (flowLP - prevMassFlowOut) / dt;
            prevMassFlowOut = flowLP;

            // Smooth the derivative
            smoothDMdt = alpha * smoothDMdt + (1.0 - alpha) * rawDerivative;

            // Far‑field monopole pressure
            double pressure = smoothDMdt * scaleFactor * Gain;

            // Soft clip to ±1 (should rarely trigger now)
            return (float)pressure;
        }
    }
}