Tampermonkey for Aliexpress order details page to amortise the shipping, discount and tax into the item price

aliexpress-amortise-shipping-discount-tax.js

// ==UserScript==
// @name         Adjust order details to amortize shipping, discount and tax into item prices
// @namespace    https://gist.githubusercontent.com/sleemanj/a56415ef7c9b8983888a7d7ec8686eb2
// @updateURL    https://gist.githubusercontent.com/sleemanj/a56415ef7c9b8983888a7d7ec8686eb2/raw/aliexpress-amortise-shipping-discount-tax.js
// @downloadURL  https://gist.githubusercontent.com/sleemanj/a56415ef7c9b8983888a7d7ec8686eb2/raw/aliexpress-amortise-shipping-discount-tax.js
// @version      1.0
// @description  Adjust order details to amortize shipping, discount and tax into item prices
// @author       James Sleeman
// @match        *://trade.aliexpress.com/order_detail.htm*
// @grant        GM_addStyle
// ==/UserScript==

(function(){

  // Leave null to calculate tax rate, or set to, eg 0.15 for 15%
  var taxRate = null;

  // Sum how many items are in the order
  var totalItems  = 0;
  Array.from(document.getElementsByClassName('price')).forEach( function(i){
    if(i.tagName.toLowerCase() == 'td')
    {
        var qty  = parseFloat(i.parentNode.querySelector('.quantity').title);
        totalItems += qty;
    }
  });

  // The item price and shipping price are BEFORE discount (financial tab)
  var preDiscountProducts =
      parseFloat(document.querySelector('td.product-price').innerText.replace(/[^0-9.]+/, ''));

  var preDiscountShipping =
      parseFloat(document.querySelector('td.shipping-price').innerText.replace(/[^0-9.]+/, ''));

  var preDiscountProductPlusShipping = preDiscountProducts + preDiscountShipping;

  // The tax is calculated after the discount (financial tab)
  var totalTax =
      parseFloat(document.querySelector('td.tax-price').innerText.replace(/[^0-9.]+/, ''));

  // as is the total (includes tax, this is the amount actually paid) (financial tab)
  var finalTotal =
      parseFloat(document.querySelector('td.order-price').innerText.replace(/[^0-9.]+/, ''));

  // Subtract the tax
  var afterDiscountProductPlusShipping = finalTotal - totalTax;
  var discountCalculated =  preDiscountProductPlusShipping - afterDiscountProductPlusShipping;

  // Work out how much we need to reduce that by
  var reductionPercent = afterDiscountProductPlusShipping / preDiscountProductPlusShipping;

  // Work that forward
  var afterDiscountShipping = preDiscountShipping * reductionPercent;
  var afterDiscountProducts = preDiscountProducts * reductionPercent;

  if(taxRate === null)
  {
    taxRate = (totalTax / (afterDiscountShipping + afterDiscountProducts));
    console.log("Calculated Tax Rate: " + taxRate);
  }

  console.log("Total Item Count: " + totalItems);
  console.log("Discount (calculated): " + discountCalculated.toFixed(2));
  console.log("After discount products: " + afterDiscountProducts.toFixed(2));
  console.log("After discount shipping: " + afterDiscountShipping.toFixed(2));
  console.log("After discount product + shipping: " + (afterDiscountShipping + afterDiscountProducts).toFixed(2));
  console.log("After discount inc Tax (calculated): " + ((afterDiscountShipping + afterDiscountProducts)*(1+taxRate)).toFixed(2));

  // Record adjusted GST inclusive product+shipping item totals on the
  var crossCheckTotal = 0;
  Array.from(document.getElementsByClassName('price')).forEach( function(i){
    if(i.tagName.toLowerCase() == 'td')
    {
        var qty  = parseFloat(i.parentNode.querySelector('.quantity').title);
        var unit = parseFloat(i.title);
        var adjustedUnit = ((unit * reductionPercent) + (afterDiscountShipping / totalItems)) * (1+taxRate);
        crossCheckTotal += adjustedUnit * qty;

        i.innerHTML += '<div title="Including Tax and Amortised Shipping">('+adjustedUnit.toFixed(3)+')</div>';
    }
  });

  console.log("Crosscheck Total: " + crossCheckTotal.toFixed(2) + " (this should be the same as the total actually paid)");
})();