TinyChan

class DelayLine{
  constructor(options={}){
    const{
      maxDelayInSamples=44100,numChannels=2,sampleRate=44100,interpolationType="linear"
    }=options;
    this.interpolationType=interpolationType;
    this.sampleRate=sampleRate;
    this.numChannels=numChannels;
    this.maxDelay=maxDelayInSamples;
    this.totalSize=Math.max(4,maxDelayInSamples+2);
    //circular buffer for each channel
    this.buffer=Array.from({length:numChannels},()=>new Array(this.totalSize).fill(0));
    this.writePos=new Array(numChannels).fill(0);
    this.readPos=new Array(numChannels).fill(0);
    this.v=new Array(numChannels).fill(0); //for Thiran interpolation
    this.setDelay(0); //initialize delay parameters
  }
  setDelay(newDelay){
    const upperLimit=this.totalSize-2;
    this.delay=Math.max(0,Math.min(newDelay,upperLimit));
    this.delayInt=Math.floor(this.delay);
    this.delayFrac=this.delay-this.delayInt;
    this.updateInternalVariables();
  }
  updateInternalVariables(){
    switch(this.interpolationType){
      case"lagrange3rd":
        if(this.delayFrac<2&&this.delayInt>=1){
          this.delayFrac++;this.delayInt--;
        }
      break;
      case"thiran":
        if(this.delayFrac<.618&&this.delayInt>=1){
          this.delayFrac++;this.delayInt--;
        }
        this.alpha=(1-this.delayFrac)/(1+this.delayFrac);
      break;
    }
  }
  pushSample(channel,sample){
    this.buffer[channel][this.writePos[channel]]=sample;
    this.writePos[channel]=(this.writePos[channel]+this.totalSize-1)%this.totalSize;
  }
  popSample(channel,delayInSamples=-1,updateReadPointer=true){
    if(delayInSamples>=0)this.setDelay(delayInSamples);
    let result;
    switch(this.interpolationType){
      case"none":result=this.interpolateNone(channel);break;
      case"linear":result=this.interpolateLinear(channel);break;
      case"lagrange3rd":result=this.interpolateLagrange3rd(channel);break;
      case"thiran":result=this.interpolateThiran(channel);break;
    }
    if(updateReadPointer)
      this.readPos[channel]=(this.readPos[channel]+this.totalSize-1)%this.totalSize;
    return result;
  }
  //interpolation methods
  interpolateNone(channel){
    const index=(this.readPos[channel]+this.delayInt)%this.totalSize;
    return this.buffer[channel][index];
  }
  interpolateLinear(channel){
    const idx1=(this.readPos[channel]+this.delayInt)%this.totalSize,
          idx2=(idx1+1)%this.totalSize,
          y1=this.buffer[channel][idx1],y2=this.buffer[channel][idx2];
    return y1+this.delayFrac*(y2-y1);
  }
  interpolateLagrange3rd(channel){
    const idx1=(this.readPos[channel]+this.delayInt)%this.totalSize,
          idx2=(idx1+1)%this.totalSize,idx3=(idx2+1)%this.totalSize,idx4=(idx3+1)%this.totalSize,
          [y1,y2,y3,y4]=[
      this.buffer[channel][idx1],
      this.buffer[channel][idx2],
      this.buffer[channel][idx3],
      this.buffer[channel][idx4]
    ],d=this.delayFrac,d1=d-1,d2=d-2,d3=d-3;
    return y1*(-d1*d2*d3/6)+d*(
      y2*(d2*d3*.5)+
      y3*(-d1*d3*.5)+
      y4*(d1*d2/6)
    );
  }
  interpolateThiran(channel){
    const idx1=(this.readPos[channel]+this.delayInt)%this.totalSize,idx2=(idx1+1)%this.totalSize,
          [y1,y2]=[this.buffer[channel][idx1],this.buffer[channel][idx2]],
          output=this.delayFrac<1e-9?y1:y2+this.alpha*(y1-this.v[channel]);
    this.v[channel]=output;
    return output;
  }
  //utility methods
  reset(){
    this.writePos.fill(0);this.readPos.fill(0);this.v.fill(0);
    this.buffer.forEach(ch=>ch.fill(0));
  }
  setMaxDelay(samples){
    this.totalSize=Math.max(4,samples+2);
    this.buffer=Array.from({length:this.numChannels},()=>new Array(this.totalSize).fill(0));
    this.reset();
  }
}
// === Usage example ===
let delay=new DelayLine({
  maxDelayInSamples:8000,
  numChannels:1,
  interpolationType:"lagrange3rd"
}),last=0;
return t=>{
  let o=(sin(PI*2*300*t)*(1-t%.3)**90)+(sin(PI*2*800*t)*(1-t%.45)**100)*.5;
  delay.pushSample(0,o-last*.7);
  delay.setDelay(1000+sin(t*2.5)*1000);
  last=delay.popSample(0);
  return Math.tanh(o+last);
};