Casual PM: Sum up remaining effort tampermonkey script

script.js

// ==UserScript==
// @name         Calculate remaining effort
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Sums of the effort of all tasks that are not yet finished. 1 day is counted as 8 hours.
// @author       Jan Thomä
// @match        https://app.casual.pm/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    function toSeconds(value) {
        if (value === null) {
            return 0;
        }
        var regex = /^(([0-9]+)d *)?(([0-9]+)h *)?(([0-9]+)m *)?$/;
        var match = regex.exec(value);
        if (match === null) {
            return 0;
        }
        var days = 0;
        var hours = 0;
        var minutes = 0;
        if (match[1]) {
            days += parseInt(match[2]);
        }
        if (match[3]) {
            hours += parseInt(match[4]);
        }
        if (match[5]) {
            minutes += parseInt(match[6]);
        }
        return (days * 8 * 3600) + (hours * 3600) + (minutes * 60);
    }

    function toPersonDays(seconds) {
        return seconds / 8 / 3600;
    }

    function calculate() {
        var efforts = document.querySelectorAll("text.g11g");
        var effortSeconds = 0;
        for(var i = 0; i < efforts.length; i++) {
            effortSeconds += toSeconds(efforts[i].textContent);
        }
        alert("Remaining effort is " + toPersonDays(effortSeconds) + " person days." );
    }

    function install() {
        var existingButton = document.querySelector("div.feedback-link");

        if (existingButton == null) {
            console.log("not yet ready...");
            window.setTimeout(install, 500);
            return;
        }

        var button = document.createElement('div');
        button.setAttribute("class", "feedback-link");
        button.setAttribute("style", "padding-right: 20px; margin-right: 5px;");
        button.textContent = "Remaining effort";
        button.onclick = calculate;

        existingButton.parentNode.insertBefore(button, existingButton);
    }

    install();
})();