HN: style unread content

Save hashes of displayed comments locally and mark new ones when displayed for the first time
当前为 2021-10-19 提交的版本，查看最新版本。
换行
// ==UserScript==
// @name        HN: style unread content 
// @description Save hashes of displayed comments locally and mark new ones when displayed for the first time
// @namespace   myfonj
// @match       https://news.ycombinator.com/*
// @grant       none
// @version     1.0.6
// @author      myfonj
// ==/UserScript==

// https://gf.qytechs.cn/en/scripts/423969/versions/new

// kinda sorta configuration
const WATCHED_ELEMENTS_SELECTOR = '.commtext, .storylink, .titlelink';
const VIEWPORT_EXPOSITION_DURATION_UNTIL_READ = 900;
const CSS_CLASSES = {
  unread: 'new',
  read: 'read',
  old: 'old'
};
// Styling. Very lame for now.
const CSS_STR = `
.${CSS_CLASSES.unread} {
  border-right: 2px solid #3F36;
  display: block;
  padding-right: 1em;
}
.${CSS_CLASSES.read} {
  border-right: 2px solid #0F03;
  display: block;
  padding-right: 1em;
}
.${CSS_CLASSES.old} {
  opacity: 0.9;
}
`;
// base64 'SHA-1' digest hash = 28 characters;
// most probably ending with '=' always(?)
const HASH_DIGEST_ALGO = 'SHA-1';

// local storage key
const LS_KEY = 'displayed_hashes_' + HASH_DIGEST_ALGO;

// actual code, yo
document.head.appendChild(document.createElement('style'))
  .textContent = CSS_STR;
// TODO mutation observer for client-side rendered pages
// not case for HN, but it will make this truly universal

const ELS_TO_WATCH = document.querySelectorAll(WATCHED_ELEMENTS_SELECTOR);
/**
 * watched DOM node -> it's text content digest
*/
const MAP_EL_HASH = new WeakMap();
/**
 * watched DOM node -> time counter ID
*/
const MAP_EL_TIMEOUT_ID = new WeakMap();
/**
 * get all "read" digests
*/
const GET_SEEN_HASHES_SET =
  () => new Set((localStorage.getItem(LS_KEY) || '').split(','));
/**
 * intersection observer callback
 */
const VIEWPORT_ENTRY_CHECKER = (entry) => {
  const TGT = entry.target;
  if (entry.isIntersecting) {
    // entered viewport
    if (MAP_EL_TIMEOUT_ID.get(TGT)) {
      // already measuring - quick re-entry
      return
    }
    // measure time in viewport
    MAP_EL_TIMEOUT_ID.set(
      TGT,
      window.setTimeout(
        processVisibleEntry,
        VIEWPORT_EXPOSITION_DURATION_UNTIL_READ
      )
    );
  } else {
    // left viewport
    MAP_EL_TIMEOUT_ID.delete(TGT);
  }
  function processVisibleEntry() {
    if (MAP_EL_TIMEOUT_ID.get(TGT)) {
      // HA! STILL in viewport!
      // mark as read
      TGT.classList.remove(CSS_CLASSES.unread);
      TGT.classList.add(CSS_CLASSES.read);
      const NEW_SET = GET_SEEN_HASHES_SET();
      NEW_SET.add(MAP_EL_HASH.get(TGT))
      MAP_EL_TIMEOUT_ID.delete(TGT);
      // not interested in this element anymore
      VIEWPORT_OBSERVER.unobserve(TGT);
      // TODO move the persistence to window unload and/or blur event for fewer LS writes
      localStorage.setItem(
        LS_KEY,
        Array.from(NEW_SET).join(',')
      );
    }
  }
}

/**
 * just a single observer for all watched elements
 */
const VIEWPORT_OBSERVER = new IntersectionObserver(
  (entries, observer) => {
    entries.forEach(_ => VIEWPORT_ENTRY_CHECKER(_));
  },
  {
    root: null,
    rootMargin: "-9%", // TODO use computed "lines" height here instead?
    threshold: 0
  }
);

const SEEN_ON_LOAD = GET_SEEN_HASHES_SET();

// compute hash, look into list and mark and observe "new" items

ELS_TO_WATCH.forEach(async el => {
  const hash = await makeHash(el.textContent);
  if (SEEN_ON_LOAD.has(hash)) {
    el.classList.add(CSS_CLASSES.old);
    return;
  }
  el.classList.add(CSS_CLASSES.unread);
  MAP_EL_HASH.set(el, hash);
  VIEWPORT_OBSERVER.observe(el);
});

/**
 * string to base64 hash digest using native Crypto API
 * @param {string} input
 */
async function makeHash (input) {
  return btoa(
    String.fromCharCode.apply(
      null,
      new Uint8Array(
        await crypto.subtle.digest(
          HASH_DIGEST_ALGO,
          (new TextEncoder()).encode(input)
        )
      )
    )
  );
};


// add some links along "threads"

const threadsLink = document.querySelector('a[href^="threads"]');
const addLink = (key) => {
  const l = threadsLink.cloneNode(true);
  l.setAttribute('href', l.getAttribute('href').replace('threads', key));
  l.textContent = key;
  threadsLink.parentNode.insertBefore(l,threadsLink);
}
['upvoted','favorites'].forEach(addLink);
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