GitHub Status - Local Time + Time Ago

Adds local time and relative time beside UTC timestamps on githubstatus.com
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// ==UserScript==
// @name         GitHub Status - Local Time + Time Ago
// @namespace    https://githubstatus.com/
// @version      1.3
// @description  Adds local time and relative time beside UTC timestamps on githubstatus.com
// @match        https://www.githubstatus.com/*
// @match        https://githubstatus.com/*
// @grant        none
// @license      MIT
// ==/UserScript==

(function () {
    'use strict';

    const DEBUG = true;

    function log(...args) {
        if (DEBUG) {
            console.log('[GitHub Status Local Time]', ...args);
        }
    }

    function warn(...args) {
        if (DEBUG) {
            console.warn('[GitHub Status Local Time]', ...args);
        }
    }

    function formatLocalDate(date) {
        const month = new Intl.DateTimeFormat('en-US', {
            month: 'short'
        }).format(date);

        const day = date.getDate();
        const year = date.getFullYear();

        const hours = String(date.getHours()).padStart(2, '0');
        const minutes = String(date.getMinutes()).padStart(2, '0');

        const timezone = new Intl.DateTimeFormat('en-US', {
            timeZoneName: 'short'
        })
            .formatToParts(date)
            .find(part => part.type === 'timeZoneName')?.value ?? '';

        return `${month} ${day}, ${year} - ${hours}:${minutes} ${timezone}`;
    }

    function formatTimeAgo(date) {
        const seconds = Math.floor((Date.now() - date.getTime()) / 1000);

        if (seconds < 5) {
            return 'just now';
        }

        if (seconds < 60) {
            return `${seconds} seconds ago`;
        }

        const minutes = Math.floor(seconds / 60);

        if (minutes < 60) {
            return `${minutes} minute${minutes === 1 ? '' : 's'} ago`;
        }

        const hours = Math.floor(minutes / 60);

        if (hours < 24) {
            return `${hours} hour${hours === 1 ? '' : 's'} ago`;
        }

        const days = Math.floor(hours / 24);

        if (days < 30) {
            return `${days} day${days === 1 ? '' : 's'} ago`;
        }

        const months = Math.floor(days / 30);

        if (months < 12) {
            return `${months} month${months === 1 ? '' : 's'} ago`;
        }

        const years = Math.floor(days / 365);

        return `${years} year${years === 1 ? '' : 's'} ago`;
    }

    function addLocalTimes() {
        const start = performance.now();

        const elements = document.querySelectorAll('.ago[data-datetime-unix]');

        log(`Processing ${elements.length} timestamp(s)`);

        let created = 0;
        let updated = 0;
        let skipped = 0;

        elements.forEach(ago => {
            const small = ago.closest('small');

            if (!small) {
                warn('Could not find <small> parent for:', ago);
                return;
            }

            const unixMs = Number(ago.dataset.datetimeUnix);

            if (!Number.isFinite(unixMs)) {
                warn('Invalid data-datetime-unix:', ago.dataset.datetimeUnix);
                return;
            }

            const date = new Date(unixMs);

            let local = small.querySelector(':scope > .tm-local-time');

            if (!local) {
                local = document.createElement('span');
                local.className = 'tm-local-time';
                small.appendChild(local);

                created++;
            }

            const newText = ` (${formatLocalDate(date)}, ${formatTimeAgo(date)})`;

            // Important: don't mutate the DOM if nothing changed.
            if (local.textContent !== newText) {
                local.textContent = newText;
                updated++;
            } else {
                skipped++;
            }
        });

        log({
            created,
            updated,
            skipped,
            durationMs: (performance.now() - start).toFixed(2)
        });
    }

    let observerTimer = null;

    const observer = new MutationObserver(mutations => {
        log(`MutationObserver fired with ${mutations.length} mutation(s)`);

        // Debounce DOM mutations to avoid repeated processing.
        clearTimeout(observerTimer);

        observerTimer = setTimeout(() => {
            log('Running update after DOM mutation');
            addLocalTimes();
        }, 100);
    });

    log('Script starting');

    addLocalTimes();

    observer.observe(document.body, {
        childList: true,
        subtree: true
    });

    log('MutationObserver started');

    setInterval(() => {
        log('Interval update');
        addLocalTimes();
    }, 30_000);
})();