using System;
using FluidSim.Interfaces;

namespace FluidSim.Core
{
    public class SoundProcessor
    {
        private readonly double dt;
        private readonly double scaleFactor;  // 1 / (4π r) and a user gain
        private double prevMassFlowOut;

        // Simple low‑pass for derivative smoothing (≈ 2‑3 ms)
        private double smoothDMdt;
        private readonly double alpha;

        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 ~ 2 ms, blocks single‑sample spikes
            double tau = 0.002;
            alpha = Math.Exp(-dt / tau);
        }

        public float Process(Port port)
        {
            // Outflow mass flow (positive = leaving pipe)
            double flowOut = -port.MassFlowRate;

            // Derivative
            double rawDerivative = (flowOut - prevMassFlowOut) / dt;
            prevMassFlowOut = flowOut;

            // Smooth the derivative to kill isolated spikes
            smoothDMdt = alpha * smoothDMdt + (1.0 - alpha) * rawDerivative;

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

            // Soft clip to ±1 for audio output (safe limit)
            float sample = (float)Math.Tanh(pressure);
            return sample;
        }
    }
}