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 ($) {
    'use strict';
    const price = (() => {
        const priceGrammar = ohm.grammar(`Price { 
                Price   = integer "р." integer "к." Price?
                integer = digit+
            }`)
        const priceVal = priceGrammar.createSemantics().addOperation('val', {
            Price: (rub, _1, kop, _2, _3) => rub.val() + kop.val() * 0.01,
            integer: _ => parseInt(_.sourceString)
        })
        const weightGrammar = ohm.grammar(`Weight {
                    Exp       = BS AnyWeight BS AnyWeight? BS
                    AnyWeight = MulWeight | Weight
                    Weight    = float (Unit1 | Unit10 | Unit1000) "."*
                    MulWeight = float ("x" | "х" | "*") Weight
                    float     = digit+ ("." digit+)? -- fl
                    Unit1     = "г"  | "мл"
                    Unit10    = "см"
                    Unit1000  = "кг" | "л" | "м" | "шт"
                    BS        = (~AnyWeight any)*
                    }`)
        const weightVal = weightGrammar.createSemantics().addOperation('val', {
            Exp: (_1, weight, _2, _3, _4) => weight.val(),
            Weight: (n, u, _1) => n.val() * u.val(),
            MulWeight: (d, _, w) => d.val() * w.val(),
            Unit1: _ => 0.001,
            Unit10: _ => 0.01,
            Unit1000: _ => 1,
            float: _ => parseFloat(_.sourceString)
        })
        const interpret = (grammar, semantics, text) => {
            const match = grammar.match(text)
            if (match.failed()) console.log(`Failed to parse [${text}] with ${match.message}`)
            return semantics(match).val()
        }
        return (price, weight) => interpret(priceGrammar, priceVal, price) / interpret(weightGrammar, weightVal, weight)
    })()
    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 => {
        try {
            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 link = template.clone()
            $(div).find('a.fa').replaceWith(link)
            link.text(normalizedPrice.toFixed(2))
            const url = (R.test(/e-dostavka/, location.host) ? R.identity : R.flip)(R.replace)('e-dostavka', 'gipermall', $(div).find('a.fancy_ajax').attr('href'))
            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 diff = (1 - competingPrice / normalizedPrice) * 100
                        link.text((_, text) => `${text} (${diff > 0 ? '>' : '<'}${Math.abs(diff).toFixed(0)}%)`)
                            .prop('href', url)
                    } catch (e) { console.log(`Failed to process page ${url}`, e) }
                }
            });
        } catch (e) { console.log(`Failed to process product card with ${$(div).find('a.fancy_ajax').text()}`, e) }
    });
})(unsafeWindow.jQuery); // somehow, when @including jquery, infinite scroll stops working.