// Store the last read post for each thread and scroll to it automatically
if (location.pathname.indexOf("/res/") >= 0) {
  let main = function () {
    let maxThreads = 300;
    let delay = 500;
    let storageKey = "lastRead";
    let lastRead = JSON.parse(localStorage.getItem(storageKey)) || {};
    let highlighted = null;
    let scrollTimer = null;
    let scrollContainer = document.getElementById("mainPanel");

    function highlight(post) {
      if (highlighted) highlighted.style.borderBottom = "";
      highlighted = post;
      highlighted.style.borderBottom = "dashed 1px #555";
    }

    function onScroll() {
      let scrollBottom = scrollContainer.scrollTop + scrollContainer.offsetHeight;
      let posts = document.getElementsByClassName("postCell");
      let lastReadPost = null;
      for (let post of posts) {
        if (post.offsetTop + post.offsetHeight > scrollBottom) break;
        lastReadPost = post;
      }
      if (lastReadPost) {
        delete lastRead[location.pathname];
        lastRead[location.pathname] = Number(lastReadPost.id);
        let keys = Object.keys(lastRead);
        if (keys.length > maxThreads) delete lastRead[keys[0]];
        localStorage.setItem(storageKey, JSON.stringify(lastRead));
      }
    }

    if (lastRead[location.pathname]) {
      let lastReadPost = document.getElementById(lastRead[location.pathname]);
      if (lastReadPost) {
        highlight(lastReadPost);
        if (!location.hash) lastReadPost.scrollIntoView();
      }
    }

    scrollContainer.addEventListener("scroll", () => {
      if (scrollTimer) clearTimeout(scrollTimer);
      scrollTimer = setTimeout(onScroll, delay);
    });

    window.addEventListener("storage", (event) => {
      if (event.key === storageKey) lastRead = JSON.parse(event.newValue) || {};
    });

    let refreshButton = document.getElementById("refreshButton");
    if (refreshButton)
      refreshButton.addEventListener("click", () => {
        let posts = document.getElementsByClassName("postCell");
        if (posts.length) highlight(posts[posts.length - 1]);
      });
  };

  document.readyState === "loading" ? window.addEventListener("DOMContentLoaded", main) : main();
}