How to Build a Tax Title Calculator

const STATE_RATES = {
  CA: { salesTax: 0.0725, titleFee: 23, registration: 65, plateFee: 28, docFeeCap: null },
  TX: { salesTax: 0.0625, titleFee: 33, registration: 51.75, plateFee: 0, docFeeCap: 150 },
  FL: { salesTax: 0.06, titleFee: 77.25, registration: 27.60, plateFee: 28, docFeeCap: 899 },
  NY: { salesTax: 0.08, titleFee: 50, registration: 32.50, plateFee: 25, docFeeCap: 175 },
  IL: { salesTax: 0.0625, titleFee: 150, registration: 151, plateFee: 0, docFeeCap: 324.24 },
  OR: { salesTax: 0, titleFee: 98.50, registration: 122, plateFee: 24.50, docFeeCap: null },
  };

  function calculateVehicleFees(purchasePrice, state, options = {}) {
  const { isNewPlate = true, docFee = 0, localTaxRate = 0, tradeInValue = 0 } = options;
  const rates = STATE_RATES[state];
  if (!rates) throw new Error('State not found');

  const taxableAmount = Math.max(0, purchasePrice - tradeInValue);
  const salesTax = taxableAmount * (rates.salesTax + localTaxRate);
  const plateCost = isNewPlate ? rates.plateFee : 0;
  const cappedDocFee = rates.docFeeCap ? Math.min(docFee, rates.docFeeCap) : docFee;

  const totalFees = salesTax + rates.titleFee + rates.registration + plateCost + cappedDocFee;

  return {
    purchasePrice,
    tradeInCredit: tradeInValue,
    salesTax: Math.round(salesTax * 100) / 100,
    titleFee: rates.titleFee,
    registration: rates.registration,
    plateFee: plateCost,
    docFee: cappedDocFee,
    totalFees: Math.round(totalFees * 100) / 100,
    outTheDoor: Math.round((purchasePrice + totalFees) * 100) / 100
  };
  }