Advent of Code Day Navigation Links

This adds forward and backwards links to each day's page.

You will need to install an extension such as Tampermonkey, Greasemonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Userscripts to install this script.

You will need to install an extension such as Tampermonkey to install this script.

You will need to install a user script manager extension to install this script.

(I already have a user script manager, let me install it!)

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

(I already have a user style manager, let me install it!)

// ==UserScript==
// @name            Advent of Code Day Navigation Links
// @namespace       Violentmonkey Scripts
// @match           https://adventofcode.com/*/day/*
// @grant           none
// @version         1.0
// @author          -
// @description     This adds forward and backwards links to each day's page.
// @author          josh
// @namespace       https://gitlab.com/userscript4/advent-of-code-day-nav
// @supportURL      https://gitlab.com/userscript4/advent-of-code-day-nav/-/issues
// @license         MIT
// ==/UserScript==

/**
 * Return the url of the requested day.
 * If less than 1 or greater than 25 provide a url to the overview page.
 * @param {number} day
 * @returns {string} A url to the requested day
 */
function makeURL(day) {
    if (day < 1 || day > 25) {
        return window.location.href.replace(/\/day\/.*/, '');
    }
    return window.location.href.replace(/(?<=\/day\/).*/, day);
}

/**
 * Create an anchor tag.
 * @param {number} day 
 * @param {string} text 
 * @returns {HTMLAnchorElement}
 */
function makeAnchor(day, text) {
    const anchor = document.createElement('a');
    anchor.href = makeURL(day);
    anchor.textContent = text;
    return anchor
}

/**
 * Find the title, extract the day number, replace the `---` with links.
 */
function addNavigationLinks() {
    const title = document.querySelector('article.day-desc > h2');
    const currentDay = parseInt(title.textContent.match(/(?<=Day )[0-9]+(?=:)/)[0]);
    title.textContent = title.textContent.match(/^--- (.*?) ---$/)[1];
    title.prepend(makeAnchor(currentDay - 1, '<-- '));
    title.append(makeAnchor(currentDay + 1, ' -->'));
}

addNavigationLinks();