Save hashes of displayed comments locally and mark new ones when displayed for the first time
Per
// ==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 1.0.4
// @author myfonj
// ==/UserScript==
// https://greasyfork.org/en/scripts/423969/versions/new
// kinda sorta configuration
const SELECTOR = '.commtext, .storylink';
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} { /* nothing */ }
`;
// base64 'SHA-1' digest hash = 28 characters; most probably ending with '=' always (?)
// could be used for splitting perhaps, but not used for it now.
const HASH_DIGEST_ALGO = 'SHA-1';
// 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(SELECTOR);
const MAP_EL_HASH = new WeakMap();
const MAP_EL_TIMEOUT = new WeakMap();
const LS_KEY = 'displayed_hashes_' + HASH_DIGEST_ALGO;
const SEEN_HASH_LIST = new Set((localStorage.getItem(LS_KEY) || '').split(','));
const VIEWPORT_ENTRY_CHECKER = (entry) => {
const TGT = entry.target;
if (entry.isIntersecting) {
// entered viewport
if (MAP_EL_TIMEOUT.get(TGT)) {
// already measuring - quick re-entry
return
}
// measure time in viewport
MAP_EL_TIMEOUT.set(
TGT,
window.setTimeout(processVisibleEntry, VIEWPORT_EXPOSITION_DURATION_UNTIL_READ)
);
} else {
// left viewport
MAP_EL_TIMEOUT.delete(TGT);
}
function processVisibleEntry() {
if (MAP_EL_TIMEOUT.get(TGT)) {
// HA! STILL in viewport!
// mark as read
TGT.classList.remove(CSS_CLASSES.unread);
TGT.classList.add(CSS_CLASSES.read);
SEEN_HASH_LIST.add(MAP_EL_HASH.get(TGT))
MAP_EL_TIMEOUT.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(SEEN_HASH_LIST).join(',')
);
}
}
}
// initialize single observer
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
}
);
// 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_HASH_LIST.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 base54 hash digest using native Crypto API
async function makeHash (input) {
return btoa(
String.fromCharCode.apply(
null,
new Uint8Array(
await crypto.subtle.digest(
HASH_DIGEST_ALGO,
(new TextEncoder()).encode(input)
)
)
)
);
};