search_hobune_for_unavailable.user.js

// ==UserScript==
// @name        Search Hobune for unavailable video IDs
// @namespace   hobune.stream
// @match       https://www.youtube.com/watch
// @grant       GM_xmlhttpRequest
// @connect     hobune.stream
// @version     1.1
// @author      Rebane
// @description 10/31/2020, 3:47:50 PM
// ==/UserScript==

let hobuneEndpoints = ["https://hobune.stream/videos/", "https://hobune.stream/tpa-h/videos/"];
let urlParams = new URLSearchParams(window.location.search);
let vidID = urlParams.get('v').replace(/[^a-zA-Z0-9_-]/g, "");

window.addEventListener('load', () => {setTimeout(detectRemovedVideo, 500)}, false);

function detectRemovedVideo(){
  let element = document.querySelector("div.promo-title.style-scope.ytd-background-promo-renderer");
  if (!element)
    return;
  let msg = document.createElement("P");
  msg.classList.add("hobunecheck");
  msg.innerText = "Checking Hobune for this video...";
  element.appendChild(msg);
  checkHobuneEndpoints();
}

function checkHobuneEndpoints(){
    GM_xmlhttpRequest ( {
        method:     'GET',
        url:        hobuneEndpoints[0] + vidID,
        onload:     function (response) {
                        if (response.status == 200){
                          /*
                           * Unused code for retrieving the title, not that it is not html escaped in this form.
                           * let title = response.responseText.match(/<title>(.*?)<\/title>/)[1];
                           */
                          document.getElementsByClassName("hobunecheck")[0].innerHTML = `Video found: <a href="${hobuneEndpoints[0] + vidID}">${vidID}</a>`;
                        } else {
                          hobuneEndpoints.shift();
                          if (hobuneEndpoints.length > 0){
                            checkHobuneEndpoints();
                          } else {
                            document.getElementsByClassName("hobunecheck")[0].innerText = "Couldn't find this video on Hobune.";
                          }
                        }
                    }
    } );
}