// ==UserScript==
// @name         Links to Next and Previous Posts
// @namespace    https://greasyfork.org/en/users/163551-vannius
// @version      1.70
// @license      MIT
// @description  Add links to next and previous posts to each post
// @author       Vannius
// @match        https://www.alternatehistory.com/forum/threads/*
// @match        https://forums.spacebattles.com/threads/*
// @match        https://forums.sufficientvelocity.com/threads/*
// @match        https://forum.questionablequesting.com/threads/*
// @grant        none
// @downloadURL none
// ==/UserScript==

(function () {
    // Make <li> tag with new link.
    const makeLink = (id, title, symbol) => {
        const newLink = document.createElement('a');
        newLink.href = '#' + id;
        newLink.title = title;
        newLink.appendChild(document.createTextNode(symbol));
        newLink.addEventListener('click', function(e) {
            e.preventDefault();
            document.getElementById(id).scrollIntoView();
        }, false);

        const liTag = document.createElement('li');
        liTag.appendChild(newLink);
        return liTag;
    }

    if (window.location.hostname == 'forum.questionablequesting.com') {
        const messageTags = document.querySelectorAll('li.message');
        const ids = [...messageTags].map(x => x.id);

        for (let i = 0; i < messageTags.length; i++) {
            const ulTag = document.createElement('ul');
            ulTag.style.listStyle = 'none';
            ulTag.style.display = 'flex';

             // Add a link to current post
            if (i === 0) {
                const currentPost = makeLink(ids[i], "Current post", '◇');
                ulTag.appendChild(currentPost);
            }

            // Add a link to prev post
            if (i !== 0) {
                const prevPost = makeLink(ids[i - 1], "Prev post", '▲');
                ulTag.appendChild(prevPost);
            }

            // Add a link to next post
            if (i !== messageTags.length - 1) {
                const nextPost = makeLink(ids[i + 1], "Next post", '▼');
                ulTag.appendChild(nextPost);
            }

            // Add a link to current post
            if (i === messageTags.length - 1) {
                const currentPost = makeLink(ids[i], "Current post", '◇');
                ulTag.appendChild(currentPost);
            }

            const userBlockTag = messageTags[i].querySelector('.userText');
            userBlockTag.appendChild(ulTag);
        }
    } else {
        // Get message ids from messageTags and make in hashLinks
        const messageTags = [...document.querySelectorAll('.message-attribution-opposite--list > li')]
        .filter(x => /^#[\d,]+$/.test(x.textContent.trim()));
        const ids = messageTags.map(x => x.closest('article').id);

        for (let i = 0; i < messageTags.length; i++) {
            // Add a link to next post
            if (i !== messageTags.length - 1) {
                const nextPost = makeLink(ids[i + 1], "Next post", '▼');
                messageTags[i].parentElement.appendChild(nextPost);
            }

            // Add a link to prev post
            if (i !== 0) {
                const prevPost = makeLink(ids[i - 1], "Prev post", '▲');
                messageTags[i].parentElement.insertBefore(prevPost, messageTags[i]);
            }

            // Add a link to current post
            if (i === 0 || i === messageTags.length - 1) {
                const currentPost = makeLink(ids[i], "Current post", '◇');
                if (i === 0) {
                    messageTags[i].parentElement.insertBefore(currentPost, messageTags[i]);
                } else if (i === messageTags.length - 1) {
                    messageTags[i].parentElement.appendChild(currentPost);
                }
            }
        }
    }
})();