function fmt(n){
  if(Math.abs(n)>=1e6) return '$'+(n/1e6).toFixed(2)+'M';
  return '$'+n.toLocaleString('en-US',{minimumFractionDigits:0,maximumFractionDigits:0});
}

function calculate(){
  var init=parseFloat(document.getElementById('initialInvestment').value)||0;
  var monthly=parseFloat(document.getElementById('monthlyContribution').value)||0;
  var years=parseInt(document.getElementById('holdingYears').value)||1;
  var yieldPct=(parseFloat(document.getElementById('dividendYield').value)||0)/100;
  var divGrowth=(parseFloat(document.getElementById('dividendGrowth').value)||0)/100;
  var priceGr=(parseFloat(document.getElementById('priceGrowth').value)||0)/100;
  var drip=document.getElementById('drip').checked;
  if(years<1) years=1;
  if(years>50) years=50;
  var annualContrib=monthly*12;
  var dripVal=init,dripCumDiv=0,noDripVal=init,noDripCumDiv=0,rows=[];
  for(var y=1;y<=years;y++){
    var totalContributed=init+annualContrib*y;
    var effYield=yieldPct*Math.pow(1+divGrowth,y-1);
    var dripStartVal=dripVal;
    var dripEndPreDiv=dripStartVal*(1+priceGr)+annualContrib*(1+priceGr*0.5);
    var dripAvgVal=(dripStartVal+dripEndPreDiv)/2;
    var dripAnnualDiv=Math.max(0,effYield*dripAvgVal);dripCumDiv+=dripAnnualDiv;dripVal=dripEndPreDiv+dripAnnualDiv;
    var noDripStartVal=noDripVal;
    var noDripEndPreDiv=noDripStartVal*(1+priceGr)+annualContrib*(1+priceGr*0.5);
    var noDripAvgVal=(noDripStartVal+noDripEndPreDiv)/2;
    var noDripAnnualDiv=Math.max(0,effYield*noDripAvgVal);noDripCumDiv+=noDripAnnualDiv;noDripVal=noDripEndPreDiv;
    rows.push({year:y,totalContrib:totalContributed,dripEnd:dripVal,noDripEnd:noDripVal,annDiv:drip?dripAnnualDiv:noDripAnnualDiv,cumDiv:drip?dripCumDiv:noDripCumDiv,diff:dripVal-(noDripVal+noDripCumDiv)});
  }
  var last=rows[rows.length-1];
  document.getElementById('sumPortfolio').textContent=fmt(drip?last.dripEnd:last.noDripEnd);
  document.getElementById('sumDividends').textContent=fmt(last.cumDiv);
  document.getElementById('sumDripDiff').textContent=fmt(last.diff);
  var tbody=document.getElementById('resultsBody');tbody.innerHTML='';
  rows.forEach(function(r){var tr=document.createElement('tr');tr.innerHTML='<td>'+r.year+'</td><td>'+fmt(r.totalContrib)+'</td><td>'+fmt(r.dripEnd)+'</td><td>'+fmt(r.noDripEnd)+'</td><td>'+fmt(r.annDiv)+'</td><td>'+fmt(r.cumDiv)+'</td><td>'+fmt(r.diff)+'</td>';tbody.appendChild(tr);});
}

document.addEventListener('DOMContentLoaded',function(){
  calculate();
  ['initialInvestment','monthlyContribution','holdingYears','dividendYield','dividendGrowth','priceGrowth','drip'].forEach(function(id){var el=document.getElementById(id);if(el)el.addEventListener('input',calculate);});
});