Directly message the author of a Scratch post

scratch-messenger.user.js

// ==UserScript==
// @name        Scratch Messenger
// @namespace   ScratchMessenger
// @author      Zro617
// @description Lets you quickly write a message directly to the author of a forum post on Scratch
// @include     https://scratch.mit.edu/discuss/topic/*
// @version     1.1.1
// @grant       none
// ==/UserScript==
/*
VERSION HISTORY
1.0 - Released
1.1 - Lifted character maximum, split large message into chunks that attach to the parent chunk, added spam prevention
1.1.1 - Oops, reset character partition limit to 500
*/
function sendComment(user, csrf, comment, parentid, success, fail) {
  var xhr = new XMLHttpRequest();
  xhr.open('POST', 'https://scratch.mit.edu/site-api/comments/user/' + user + '/add/', true);
  xhr.responseType = 'document';
  xhr.setRequestHeader('X-CSRFToken', csrf),
  xhr.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
  xhr.onload = function () {
    this.status == 200 ? success(xhr) : fail(xhr);
  };
  xhr.send(JSON.stringify({
    content: comment,
    parent_id: parentid,
    commentee_id: ''
  }));
}
function getCSRF() {
  return document.cookie.match(/scratchcsrftoken=([0-9a-zA-Z]+)/);
}
function getPosts() {
  return document.getElementsByClassName('blockpost roweven firstpost');
}
function getUsers() {
  return document.getElementsByClassName('black username');
}
function chunkify(comment, length) {
  var commentChunks = [];
  if (comment.length > length) {
    for (var i = 0, chk; i < comment.length; ) {
      if (i < comment.length - length) {
        chk = comment.substring(i, i + length - 3) + '...';
        i += length - 3;
      } else {
        chk = comment.substring(i);
        i += length;
      }
      commentChunks.push(chk);
    }
  } else {
    commentChunks.push(comment);
  }
  return commentChunks;
}

if (!getCSRF()) return;
var posts = getPosts(), users = getUsers();
if (!posts.length) return;

for (var p = 0, msgauthor, btn, user, ul; p < posts.length; p++) {
  user = users[p].innerHTML;
  msgauthor = document.createElement('li');
  msgauthor.setAttribute('class', 'message-author');
  btn = document.createElement('a');
  btn.setAttribute('id', user);
  //btn.setAttribute("id",posts[p].id.match(/\d+/)[0]);
  btn.innerHTML = 'Message ' + user;
  btn.onclick = function () {
    if (this.innerHTML != 'Message '+this.id) return alert("Please wait 30 seconds before messaging again"); // avoid spamming
    var clicked = this,
        user = this.id,
        csrf = getCSRF()[1],
        parentid = "",
        chunk = 0,
        comment = prompt('Write your message to ' + user);
    if (!comment) return;
    comment = chunkify(comment, 500);
    
    clicked.innerHTML = "Posting...";
    function sendChunk() {
      console.log('Sending chunk '+chunk+'...');
        sendComment(user, csrf, comment[chunk], parentid, function(x) {
          if (parentid == ""){
            parentid = x.responseXML.getElementsByClassName('comment')[0].getAttribute('data-comment-id'); // can't user querySelector, seriously?!?!
            console.log('Comment ID retrieved: '+parentid);
          }
          console.log('Chunk '+chunk+' of comment sent.');
          if (chunk == comment.length-1) {
            clicked.innerHTML = "Message sent!";
            window.setTimeout(function(){clicked.innerHTML='Message '+user;},30000); // wait 30 seconds before messaging same user
            alert("Message successfully sent!");
            return; 
          }
          chunk++;
          window.setTimeout(sendChunk,3000); // avoid triggering spam filter
        }, function(x) { alert("Oops! Something went wrong...") }
        );
    }
    sendChunk();
  };
  msgauthor.appendChild(btn);
  msgauthor.appendChild(document.createTextNode(' | '));
  ul = posts[p].getElementsByClassName('postfootright') [0].getElementsByTagName('ul') [0];
  ul.insertBefore(msgauthor, ul.firstChild.nextSibling);
}