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YouTube Auto-Resume

This script automatically tracks and restores your YouTube playback position. This user script remembers where you left off in any video—allowing you to seamlessly continue watching even after navigating away or reloading the page. It saves your progress for each video for up to 3 days (configurable) and automatically cleans up outdated entries, ensuring a smooth and uninterrupted viewing experience every time.

// ==UserScript==
// @name                YouTube Auto-Resume
// @icon                https://www.youtube.com/img/favicon_48.png
// @author              ElectroKnight22
// @namespace           electroknight22_youtube_auto_resume_namespace
// @version             1.3.2
// @match               *://www.youtube.com/*
// @match               *://www.youtube-nocookie.com/*
// @exclude             *://www.youtube.com/live_chat*
// @grant               GM.getValue
// @grant               GM.setValue
// @grant               GM.deleteValue
// @grant               GM.listValues
// @grant               GM_getValue
// @grant               GM_setValue
// @grant               GM_deleteValue
// @grant               GM_listValues
// @license             MIT
// @description         This script automatically tracks and restores your YouTube playback position. This user script remembers where you left off in any video—allowing you to seamlessly continue watching even after navigating away or reloading the page. It saves your progress for each video for up to 3 days (configurable) and automatically cleans up outdated entries, ensuring a smooth and uninterrupted viewing experience every time.
// ==/UserScript==

/*jshint esversion: 11 */

(function () {
    "use strict";

    let useCompatibilityMode = false;

    // script will save playback time for 3 days by default, edit this value to change. Old data is only cleared on script load. This value will be reset to 3 if the script is updated.
    const daysToRemember = 3;

    const GMCustomGetValue = useCompatibilityMode ? GM_getValue : GM.getValue;
    const GMCustomSetValue = useCompatibilityMode ? GM_setValue : GM.setValue;
    const GMCustomDeleteValue = useCompatibilityMode ? GM_deleteValue : GM.deleteValue;
    const GMCustomListValues = useCompatibilityMode ? GM_listValues : GM.listValues;

    async function resumePlayback(moviePlayer, videoElement) {
        if (videoElement.inPlaylist && videoElement.playlistType !== 'WL') return;
        if (videoElement.timeSpecified || videoElement.resumed || videoElement.isLive) return;
        try {
            const playerSize = moviePlayer.getPlayerSize();
            if (playerSize.width === 0 || playerSize.height === 0) return;
            const playbackStatus = await GMCustomGetValue(videoElement.videoId);
            const lastPlaybackTime = playbackStatus?.timestamp;
            const currentPlaybackTime = moviePlayer.getCurrentTime();
            const timeDiff = Math.abs(currentPlaybackTime - lastPlaybackTime);
            if (!isNaN(timeDiff) && lastPlaybackTime !== 0 && timeDiff > 1) {
                moviePlayer.seekTo(lastPlaybackTime, true, {
                    skipBufferingCheck: true
                });
                videoElement.resumed = true;
            }
        } catch (error) {
            throw new Error("Failed to resume playback due to this error. Error: " + error);
        }
    }

    function handleVideoLoad(event) {
        try {
            const moviePlayer = event.target?.player_;
            const videoElement = event.target?.querySelector('video');
            videoElement.videoId = moviePlayer?.getVideoData().video_id;
            videoElement.isLive = moviePlayer?.getVideoData().isLive;
            videoElement.resumed = false;
            videoElement.timeSpecified = new URL(window.location.href).searchParams.has('t');
            videoElement.inPlaylist = new URL(window.location.href).searchParams.has('list');
            videoElement.playlistType = new URLSearchParams(window.location.search).get('list');
            if (videoElement.autoResumeHandler) return;
            videoElement.autoResumeHandler = async () => {
                if (!moviePlayer || !videoElement.videoId) return;
                await resumePlayback(moviePlayer, videoElement);
                updatePlaybackStatus(videoElement);
            };
            videoElement.addEventListener('timeupdate', videoElement.autoResumeHandler, true);
        } catch (error) {
            throw new Error("Failed to handle video load due to this error. Error: " + error);
        }
    }

    function updatePlaybackStatus(videoElement) {
        try {
            const videoDuration = videoElement.duration;
            const currentPlaybackTime = videoElement.currentTime;
            const timeLeft = videoDuration - currentPlaybackTime;
            if (isNaN(timeLeft)) return;
            if (timeLeft < 1) {
                GMCustomDeleteValue(videoElement.videoId);
            } else {
                const currentPlaybackStatus = {
                    timestamp: currentPlaybackTime,
                    lastUpdated: Date.now()
                };
                GMCustomSetValue(videoElement.videoId, currentPlaybackStatus);
            }
        } catch (error) {
            throw new Error("Failed to update playback status due to this error. Error: " + error);
        }
    }

    async function cleanUpStoredPlaybackStatuses() {
        try {
            const videoIds = await GMCustomListValues();
            const threshold = daysToRemember * 86400 * 1000;
            for (const videoId of videoIds) {
                const storedPlaybackStatus = await GMCustomGetValue(videoId);
                if (!storedPlaybackStatus ||
                    isNaN(storedPlaybackStatus.lastUpdated) ||
                    Date.now() - storedPlaybackStatus.lastUpdated > threshold) {
                    await GMCustomDeleteValue(videoId);
                }
            }
        } catch (error) {
            throw new Error("Failed to clean up stored playback statuses due to this error. Error: " + error);
        }
    }

    function hasGreasyMonkeyAPI() {
        if (typeof GM !== 'undefined') return true;
        if (typeof GM_info !== 'undefined') {
            useCompatibilityMode = true;
            console.warn("Running in compatibility mode.");
            return true;
        }
        return false;
    }

    async function initialize() {
        try {
            if (!hasGreasyMonkeyAPI()) throw new Error("Did not detect valid Grease Monkey API");
            await cleanUpStoredPlaybackStatuses();
            window.addEventListener('yt-player-updated', (event) => {
                handleVideoLoad(event);
            }, true);
            window.addEventListener('yt-autonav-pause-player-ended', (event) => {
                const videoId = event.target?.player?.getVideoData()?.video_id;
                GMCustomDeleteValue(videoId);
            }, true);
        } catch (error) {
            throw new Error(`Error when initializing script: ${error}. Aborting script.`);
        }
    }

    initialize();
})();