e-dostavka/e-dostavka.user.js

// ==UserScript==
// @name         [e-dostavka.by, gipermall.by] price comparison
// @namespace    http://tampermonkey.net/
// @version      2
// @description  Show prices per kilo, compare between sites
// @author       nomoreknights
// @match        https://e-dostavka.by/*
// @match        https://gipermall.by/*
// @grant        unsafeWindow
// @grant        GM.xmlHttpRequest
// @require      https://cdnjs.cloudflare.com/ajax/libs/arrive/2.4.1/arrive.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.min.js
// @require      https://unpkg.com/ohm-js@0.14.0/dist/ohm.min.js
// ==/UserScript==

(function () {
    'use strict';
    const price = (() => {
        const float = n => parseFloat(n.sourceString)
        const priceG = ohm.grammar(`Price { Price = digit+ "р." digit+ "к." Price? }`)
        const priceS = priceG.createSemantics().addOperation('val', {
            Price: (rub, _2, kop, _4, _5) => float(rub) * 100 + float(kop),
        })
        const weightG = ohm.grammar(`Weight {
            Exp       = BS* AnyWeight BS* AnyWeight? BS*
            AnyWeight = MulWeight | Weight
            Weight    = float (OneUnit | ThUnit)
            OneUnit   = Dot<"г">  | Dot<"мл"> | Dot<"шт"> | Dot<"см">
            ThUnit    = Dot<"кг"> | Dot<"л"> | Dot<"м">
            Dot<R>    = R "."*
            MulWeight = float ("x" | "х" | "*") Weight
            BS        = ~AnyWeight any
            float = (digit digit* "." digit) -- fl
            	| digit+
            }`)
        const weightS = weightG.createSemantics().addOperation('val', {
            Exp: (_, weight, __, ___, _____) => weight.val(),
            Weight: (n, u) => float(n) * u.val(),
            OneUnit: _ => 1, ThUnit: _ => 1000,
            MulWeight: (d, _, w) => float(d) * w.val(),
        })
        const interpret = (g, s) => (text) => s(g.match(text))
        return (price, weight) => (interpret(priceG, priceS)(price).val() / interpret(weightG, weightS)(weight).val() / 100 * 1000)
    })()
    const $ = unsafeWindow.jQuery; // somehow, when @including jquery, infinite scroll stops working.
    const template = $("<a/>").css({
        'background-color': '#fbba00',
        'color': 'black', // default is #cb4f2b
        'padding': '2px',
        'border-radius': '5px',
        'font-size': '14px',
        'font-family': 'MyriadProCondencedBoldItalic',
        'position': 'absolute',
        'right': '5px'
    }).attr('target', '_blank')
    $(document).arrive(".products_card", { existing: true }, div => {
        const normalizedPrice = price(
            $(div).find('div > form > div.prices__wrapper > div > div.prices_block > div > div.price').text(),
            $(div).find('a.fancy_ajax').text()
        )
         const button = template.clone()
         const url = (R.test(/e-dostavka/, location.host) ? R.identity : R.flip)(R.replace)('e-dostavka', 'gipermall', $(div).find('a.fancy_ajax').attr('href'))
         $(div).find('a.fa').replaceWith(button)
         button.text(normalizedPrice.toFixed(2))
         GM.xmlHttpRequest({
             method: 'GET', url, onload: page => {
                 try {
                     const html = $($.parseHTML(page.responseText))
                     const competingPrice = price(
                         html.find('div.services_wrap:nth-child(3) > div:nth-child(1) > div:nth-child(1) > div:nth-child(1)').text(),
                         html.find('.template_1_columns > h1:nth-child(2)').text()
                     )
                     const difference = Math.abs(1 - competingPrice / normalizedPrice) * 100
                     button.text((i, _) => `${_} (${competingPrice >= normalizedPrice ? '>' : '<'}${difference.toFixed(0)}%)`).prop('href', url)
                 } catch (e) { }
             }
         });
    });
})();