/**
 * VAT Withholding Calculator
 * For Overseas Chinese Users in Hong Kong and Macao
 */

(function() {
  'use strict';

  const VAT_RATES = {
    'transportation': { rate: 9, name: 'Transportation, Postal, Telecom Services' },
    'construction': { rate: 9, name: 'Construction & Real Estate' },
    'modern': { rate: 6, name: 'Modern Services (Consulting, IT, etc.)' },
    'financial': { rate: 6, name: 'Financial & Insurance Services' },
    'lifestyle': { rate: 6, name: 'Lifestyle & Cultural Services' },
    'intangible': { rate: 6, name: 'Intangible Assets' },
    'goods': { rate: 13, name: 'Goods / Tangible Assets' },
    'processing': { rate: 13, name: 'Processing, Repair & Replacement' },
    'rental': { rate: 13, name: 'Tangible Asset Leasing' }
  };

  const SURTAX_RATES = {
    'urban': { urbanMaintenance: 7, education: 3, localEducation: 2 },
    'county': { urbanMaintenance: 5, education: 3, localEducation: 2 },
    'other': { urbanMaintenance: 1, education: 3, localEducation: 2 }
  };

  const EIT_RATE = 10;

  function formatCurrency(value) {
    return new Intl.NumberFormat('zh-CN', {
      style: 'currency',
      currency: 'CNY',
      minimumFractionDigits: 2,
      maximumFractionDigits: 2
    }).format(value);
  }

  function getServiceTypeName(value) {
    return VAT_RATES[value] ? VAT_RATES[value].name : 'Other Services';
  }

  function getVATRate(value) {
    return VAT_RATES[value] ? VAT_RATES[value].rate : 6;
  }

  function calculateWithholding(params) {
    const {
      amount = 0,
      serviceType = 'modern',
      locationType = 'urban',
      hasEstablishment = false,
      includeEIT = true,
      eitRate = EIT_RATE
    } = params;

    const amountNum = parseFloat(amount) || 0;
    if (amountNum <= 0) {
      return null;
    }

    const vatRate = getVATRate(serviceType);
    const surtax = SURTAX_RATES[locationType] || SURTAX_RATES.urban;

    const vatAmount = amountNum / (1 + vatRate / 100) * (vatRate / 100);
    const taxInclusiveTotal = amountNum;
    const vatExclusiveAmount = amountNum - vatAmount;

    const urbanTax = vatAmount * (surtax.urbanMaintenance / 100);
    const eduSurcharge = vatAmount * (surtax.education / 100);
    const localEduSurcharge = vatAmount * (surtax.localEducation / 100);
    const totalSurtax = urbanTax + eduSurcharge + localEduSurcharge;

    let eitAmount = 0;
    if (includeEIT && !hasEstablishment) {
      eitAmount = vatExclusiveAmount * (eitRate / 100);
    }

    const totalTaxes = vatAmount + totalSurtax + eitAmount;
    const netPayment = taxInclusiveTotal - totalTaxes;

    return {
      inputAmount: amountNum,
      serviceName: getServiceTypeName(serviceType),
      vatRate: vatRate,
      vatExclusiveAmount: vatExclusiveAmount,
      vatAmount: vatAmount,
      surtaxDetails: {
        urbanMaintenance: { rate: surtax.urbanMaintenance, amount: urbanTax },
        education: { rate: surtax.education, amount: eduSurcharge },
        localEducation: { rate: surtax.localEducation, amount: localEduSurcharge }
      },
      totalSurtax: totalSurtax,
      includeEIT: includeEIT,
      eitRate: eitRate,
      eitAmount: eitAmount,
      totalTaxes: totalTaxes,
      netPayment: netPayment
    };
  }

  function setText(id, value) {
    const el = document.getElementById(id);
    if (el) el.textContent = value;
  }

  function displayResults(result) {
    const resultBox = document.getElementById('result-box');
    if (!resultBox) return;

    const placeholder = document.getElementById('placeholder-text');
    const details = document.getElementById('result-details');
    if (placeholder) placeholder.style.display = 'none';
    if (details) details.style.display = 'block';

    setText('result-service-type', result.serviceName);
    setText('result-amount', formatCurrency(result.inputAmount));
    setText('result-vat-rate', result.vatRate + '%');
    setText('result-vat-exclusive', formatCurrency(result.vatExclusiveAmount));
    setText('result-vat-amount', formatCurrency(result.vatAmount));

    setText('result-urban-rate', result.surtaxDetails.urbanMaintenance.rate + '%');
    setText('result-urban-amount', formatCurrency(result.surtaxDetails.urbanMaintenance.amount));
    setText('result-edu-rate', result.surtaxDetails.education.rate + '%');
    setText('result-edu-amount', formatCurrency(result.surtaxDetails.education.amount));
    setText('result-local-edu-rate', result.surtaxDetails.localEducation.rate + '%');
    setText('result-local-edu-amount', formatCurrency(result.surtaxDetails.localEducation.amount));
    setText('result-total-surtax', formatCurrency(result.totalSurtax));

    const eitSection = document.getElementById('eit-section');
    if (eitSection) {
      if (result.includeEIT) {
        eitSection.style.display = 'block';
        setText('result-eit-rate', result.eitRate + '%');
        setText('result-eit-amount', formatCurrency(result.eitAmount));
      } else {
        eitSection.style.display = 'none';
      }
    }

    setText('result-total-taxes', formatCurrency(result.totalTaxes));
    setText('result-net-payment', formatCurrency(result.netPayment));

    resultBox.classList.add('show');
    resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
  }

  function performCalculation() {
    const form = document.getElementById('vat-calculator-form');
    if (!form) return;

    const formData = new FormData(form);
    const params = {
      amount: formData.get('amount'),
      serviceType: formData.get('service_type'),
      locationType: formData.get('location_type'),
      hasEstablishment: formData.get('has_establishment') === 'yes',
      includeEIT: formData.get('include_eit') === 'yes',
      eitRate: parseFloat(formData.get('eit_rate')) || EIT_RATE
    };

    const result = calculateWithholding(params);
    if (!result) {
      alert('Please enter a valid amount greater than zero.');
      return;
    }

    displayResults(result);
  }

  function initCalculator() {
    const calculatorForm = document.getElementById('vat-calculator-form');
    if (!calculatorForm) return;

    calculatorForm.addEventListener('submit', function(e) {
      e.preventDefault();
      performCalculation();
    });
  }

  function initMobileMenu() {
    const toggle = document.querySelector('.mobile-toggle');
    const navLinks = document.querySelector('.nav-links');

    if (toggle && navLinks) {
      toggle.addEventListener('click', function() {
        navLinks.classList.toggle('show');
      });
    }
  }

  document.addEventListener('DOMContentLoaded', function() {
    initCalculator();
    initMobileMenu();

    window.vatCalculator = {
      calculate: calculateWithholding,
      getServiceTypeName: getServiceTypeName,
      getVATRate: getVATRate,
      formatCurrency: formatCurrency
    };
  });

})();