Chrome Extension Import Duty Calculator: A Developer Guide

// popup.js
class DutyCalculator {
  constructor() {
    this.rates = {
      US: {
        deMinimis: 800,
        dutyRates: {
          general: 0.046,
          electronics: 0.025,
          clothing: 0.125,
          beauty: 0.065,
          food: 0.042
        },
        processingFee: 0,
        vat: 0
      },
      EU: {
        deMinimis: 150,
        dutyRates: {
          general: 0.027,
          electronics: 0.014,
          clothing: 0.12,
          beauty: 0.067,
          food: 0.089
        },
        processingFee: 0,
        vat: 0.21 // Average EU VAT
      },
      UK: {
        deMinimis: 135,
        dutyRates: {
          general: 0.028,
          electronics: 0.014,
          clothing: 0.11,
          beauty: 0.065,
          food: 0.076
        },
        processingFee: 0,
        vat: 0.20
      },
      CA: {
        deMinimis: 40,
        dutyRates: {
          general: 0.045,
          electronics: 0.035,
          clothing: 0.18,
          beauty: 0.085,
          food: 0.065
        },
        processingFee: 9.95,
        vat: 0.05 // GST
      },
      AU: {
        deMinimis: 1000,
        dutyRates: {
          general: 0.025,
          electronics: 0.01,
          clothing: 0.10,
          beauty: 0.05,
          food: 0.015
        },
        processingFee: 0,
        vat: 0.10 // GST
      }
    };
  }

  calculate(country, itemValue, shippingCost, category) {
    const config = this.rates[country];
    if (!config) {
      throw new Error('Unsupported country');
    }

    const totalValue = itemValue + shippingCost;
    
    // Check if below de minimis threshold
    if (totalValue <= config.deMinimis) {
      return {
        duty: 0,
        vat: 0,
        processingFee: 0,
        total: 0,
        belowDeMinimis: true,
        deMinimisThreshold: config.deMinimis
      };
    }

    // Calculate duty based on category
    const dutyRate = config.dutyRates[category] || config.dutyRates.general;
    const duty = totalValue * dutyRate;

    // Calculate VAT/GST on (value + duty)
    const vatBase = totalValue + duty;
    const vat = vatBase * config.vat;

    // Processing fees (mainly for Canada)
    const processingFee = config.processingFee;

    return {
      duty: Math.round(duty * 100) / 100,
      vat: Math.round(vat * 100) / 100,
      processingFee,
      total: Math.round((duty + vat + processingFee) * 100) / 100,
      belowDeMinimis: false,
      deMinimisThreshold: config.deMinimis
    };
  }
}

// Initialize and bind events
document.addEventListener('DOMContentLoaded', () => {
  const calculator = new DutyCalculator();
  const calculateBtn = document.getElementById('calculate');
  const resultsDiv = document.getElementById('results');

  calculateBtn.addEventListener('click', () => {
    const country = document.getElementById('country').value;
    const value = parseFloat(document.getElementById('value').value) || 0;
    const shipping = parseFloat(document.getElementById('shipping').value) || 0;
    const category = document.getElementById('category').value;

    if (!country || value <= 0) {
      alert('Please fill in all required fields');
      return;
    }

    try {
      const result = calculator.calculate(country, value, shipping, category);
      
      document.getElementById('duty-amount').textContent = `$${result.duty.toFixed(2)}`;
      document.getElementById('vat-amount').textContent = `$${result.vat.toFixed(2)}`;
      document.getElementById('processing-fee').textContent = `$${result.processingFee.toFixed(2)}`;
      document.getElementById('total-cost').textContent = `$${result.total.toFixed(2)}`;
      
      resultsDiv.classList.remove('hidden');
      
      // Save to history
      this.saveCalculation({ country, value, shipping, category, result });
    } catch (error) {
      alert(error.message);
    }
  });
});

// content.js - Extract product info from supported sites
const selectors = {
  amazon: {
    price: '#priceblock_ourprice, #priceblock_dealprice',
    title: '#productTitle',
    category: '#wayfinding-breadcrumbs_container'
  },
  ebay: {
    price: '.x-price-primary span',
    title: '.x-item-title__mainTitle',
    category: '.x-breadcrumbs'
  },
  generic: {
    price: '[data-price], .price, .product-price',
    title: 'h1, [itemprop="name"]',
    category: '.breadcrumb, .category'
  }
};

function extractProductInfo() {
  const url = window.location.hostname;
  let selectorSet = selectors.generic;
  
  if (url.includes('amazon')) selectorSet = selectors.amazon;
  else if (url.includes('ebay')) selectorSet = selectors.ebay;
  
  const getText = (sel) => {
    const el = document.querySelector(sel);
    return el ? el.textContent.trim() : null;
  };
  
  const getPrice = (sel) => {
    const el = document.querySelector(sel);
    if (!el) return null;
    const text = el.textContent.replace(/[^0-9.]/g, '');
    return parseFloat(text) || null;
  };
  
  return {
    title: getText(selectorSet.title),
    price: getPrice(selectorSet.price),
    category: getText(selectorSet.category),
    url: window.location.href
  };
}

// Listen for messages from popup
chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
  if (request.action === 'getProductInfo') {
    const info = extractProductInfo();
    sendResponse(info);
  }
});

// Fetch real-time rates from a tariff API
async function fetchTariffRates(country, hsCode) {
  try {
    const response = await fetch(`https://api.example.com/tariffs`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer YOUR_API_KEY'
      },
      body: JSON.stringify({
        country,
        hsCode,
        year: new Date().getFullYear()
      })
    });
    
    return await response.json();
  } catch (error) {
    console.error('Failed to fetch tariff rates:', error);
    return null;
  }
}