#include "soundfile.h"

int main(int argc, char** argv) {
   Options options;
   options.define("a0=d:1", "first  feedforward term");
   options.define("a1=d:1", "second feedforward term");
   options.define("a2=d:1", "third  feedforward term");
   options.define("b1=d:1", "first  feedback term");
   options.define("b2=d:1", "second feedback term");
   options.process(argc, argv);

   double a0 = options.getDouble("a0");
   double a1 = options.getDouble("a1");
   double a2 = options.getDouble("a2");
   double b1 = options.getDouble("b1");
   double b2 = options.getDouble("b2");

   SoundFileRead  insound(options.getArg(1));
   int sampleCount = insound.getSamples();
   SoundHeader    header = insound;
   header.setChannels(1);  // write only mono files
   SoundFileWrite outsound(options.getArg(2), header);

   double currin   = 0.0;   // x[n]
   double lastin   = 0.0;   // x[n-1]
   double lastin2  = 0.0;   // x[n-2]
   double currout  = 0.0;   // y[n]
   double lastout  = 0.0;   // y[n-1]
   double lastout2 = 0.0;   // y[n-2]

   // the for-loop implements the difference equation for a biquad filter: 
   //    y[n] = a0*x[n] + a1*x[n-1] + a2*x[n-2] - b1*y[n-1] - b2*y[n-2]
   for (int i=0; i<sampleCount; i++) {
      insound.incrementSample();
      lastin2  = lastin;
      lastin   = currin;
      currin   = insound.getCurrentSampleDouble(0);
      lastout2 = lastout;
      lastout  = currout;
      currout  = a0*currin + a1*lastin + a2*lastin2 - b1*lastout - b2*lastout2;
      outsound.writeSampleDouble(currout);
   }

   return 0;
}