// ==UserScript==
// @name                YouTube Auto-Resume
// @icon                https://www.youtube.com/img/favicon_48.png
// @author              ElectroKnight22
// @namespace           electroknight22_youtube_auto_resume_namespace
// @version             1.0.0
// @match               *://*.youtube.com/*
// @match               *://www.youtube-nocookie.com/*
// @grant               GM.getValue
// @grant               GM.setValue
// @grant               GM_getValue
// @grant               GM_setValue
// @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 It saves your progress for each video for up to 3 days (configurable) and automatically cleans up outdated entries, ensuring a smooth and uninterrupted viewing experience every time.
// @downloadURL none
// ==/UserScript==

/*jshint esversion: 11 */

(function () {
    "use strict";

    let playbackStatuses = {};
    let videoId;
    let useCompatibilityMode = false;

    // script will save playback time for 3 days by default, edit this value to change.
    const daysToRemember = 3;

    // Greasemonkey API Compatibility Layer
    const GMCustomGetValue = useCompatibilityMode ? GM_getValue : GM.getValue;
    const GMCustomSetValue = useCompatibilityMode ? GM_setValue : GM.setValue;

    function updateVideoStatus(event) {
        try {
            videoId = event.detail?.getVideoData().video_id;
            const videoElement = event.target?.querySelector('video');
            const lastPlaybackTime = playbackStatuses[videoId]?.timestamp;
            if (!isNaN(lastPlaybackTime)) event.detail?.seekTo(lastPlaybackTime);
            if (videoElement) videoElement.addEventListener('timeupdate', () => {
                updatePlaybackStatus(videoElement);
            }, true);
        } catch (error) {
            throw ("Failed to update video status due to this error. Error: " + error);
        }
    }

    function updatePlaybackStatus(videoElement) {
        if (!videoId) return;
        try {
            const currentPlaybackTime = videoElement.currentTime;
            if (currentPlaybackTime && currentPlaybackTime !== 0) {
                const currentPlaybackStatus = {
                    timestamp: currentPlaybackTime,
                    lastUpdated: Date.now()
                };
                playbackStatuses[videoId] = currentPlaybackStatus;
                GMCustomSetValue('playbackStatuses', playbackStatuses);
            }
        } catch (error) {
            throw ("Failed to update playback status due to this error. Error: " + error);
        }
    }

    function cleanUpStoredPlaybackStatuses() {
        let hasUpdated = false;
        for (const [key, value] of Object.entries(playbackStatuses)) {
            if (Date.now() - value.lastUpdated > daysToRemember * 24 * 60 * 60 * 1000) {
                delete playbackStatuses[key];
                hasUpdated = true;
            }
        }
        if (hasUpdated) GMCustomSetValue('playbackStatuses', playbackStatuses);
    }

    async function loadStoredPlaybackStatuses() {
        try {
            playbackStatuses = await GMCustomGetValue('playbackStatuses', {});
        } catch (error) {
            throw `Error loading stored playback statuses: ${error}. Aborting script.`;
        }
    }

    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 "Did not detect valid Grease Monkey API";
            await loadStoredPlaybackStatuses();
            window.addEventListener('yt-player-updated', (event) => {
                cleanUpStoredPlaybackStatuses();
                updateVideoStatus(event);
            }, true);
        } catch (error) {
            console.error(`Error when initializing script: ${error}. Aborting script.`);
        }
    }

    initialize();
})();