// ==UserScript==
// @name         alternatehistory.com: Links to Next and Previous Posts.
// @namespace    https://greasyfork.org/en/users/163551-vannius
// @version      1.0
// @description  Add links to next and previous posts to each post.
// @author       Vannius
// @match        https://www.alternatehistory.com/forum/threads/*
// @grant        none
// @downloadURL none
// ==/UserScript==

(function() {
    // Get hash links from divTags and store in hashLinks
    const divTags = document.getElementsByClassName('messageBarNumber');
    const hashLinks = Array.from(divTags).map((element) => element.children[0].href);
    // Very first post of thread's divTag.children[0].href don't have #.
    if (window.location.href.split('/')[6] === '') hashLinks[0] += '#' + divTags[0].parentNode.parentNode.id;

    for (let i = 0; i<divTags.length; i++){
        // Add a link to next post
        if (i != divTags.length - 1){
            const nextPost = document.createElement('a');
            nextPost.title = "Next post";
            nextPost.href = hashLinks[i + 1];
            nextPost.appendChild(document.createTextNode('▼'));
            divTags[i].appendChild(nextPost);
        }
        // Add a link to prev post
        if (i !== 0){
            const prevPost = document.createElement('a');
            prevPost.title = "Prev post";
            prevPost.href = hashLinks[i - 1];
            prevPost.appendChild(document.createTextNode('▲'));
            divTags[i].insertBefore(prevPost, divTags[i].children[0]);
        }
        // Add a link to current post
        if (i === 0 || i == divTags.length - 1){
            const currentPost = document.createElement('a');
            currentPost.title = "Current post";
            currentPost.href = hashLinks[i];
            currentPost.appendChild(document.createTextNode('◆'));
            if (i === 0)　divTags[i].insertBefore(currentPost, divTags[i].children[0]);
            else if (i == divTags.length - 1) divTags[i].appendChild(currentPost);
        }
    }
})();