// ==UserScript==
// @name              X Timeline Sync
// @description       Tracks and syncs your last reading position on Twitter/X, with manual and automatic options. Ideal for keeping track of new posts without losing your place.
// @description:de    Verfolgt und synchronisiert Ihre letzte Leseposition auf Twitter/X, mit manuellen und automatischen Optionen. Perfekt, um neue Beiträge im Blick zu behalten, ohne die aktuelle Position zu verlieren.
// @description:es    Rastrea y sincroniza tu última posición de lectura en Twitter/X, con opciones manuales y automáticas. Ideal para mantener el seguimiento de las publicaciones nuevas sin perder tu posición.
// @description:fr    Suit et synchronise votre dernière position de lecture sur Twitter/X, avec des options manuelles et automatiques. Idéal pour suivre les nouveaux posts sans perdre votre place actuelle.
// @description:zh-CN 跟踪并同步您在 Twitter/X 上的最后阅读位置，提供手动和自动选项。完美解决在查看新帖子时不丢失当前位置的问题。
// @description:ru    Отслеживает и синхронизирует вашу последнюю позицию чтения на Twitter/X с ручными и автоматическими опциями. Идеально подходит для просмотра новых постов без потери текущей позиции.
// @description:ja    Twitter/X での最後の読み取り位置を追跡して同期します。手動および自動オプションを提供します。新しい投稿を見逃さずに現在の位置を維持するのに最適です。
// @description:pt-BR Rastrea e sincroniza sua última posição de leitura no Twitter/X, com opções manuais e automáticas. Perfeito para acompanhar novos posts sem perder sua posição atual.
// @description:hi    Twitter/X पर आपकी अंतिम पठन स्थिति को ट्रैक और सिंक करता है, मैनुअल और स्वचालित विकल्पों के साथ। नई पोस्ट देखते समय अपनी वर्तमान स्थिति को खोए बिना इसे ट्रैक करें।
// @description:ar    يتتبع ويزامن آخر موضع قراءة لك على Twitter/X، مع خيارات يدوية وتلقائية. مثالي لتتبع المشاركات الجديدة دون فقدان موضعك الحالي.
// @description:it    Traccia e sincronizza la tua ultima posizione di lettura su Twitter/X, con opzioni manuali e automatiche. Ideale per tenere traccia dei nuovi post senza perdere la posizione attuale.
// @description:ko    Twitter/X에서 마지막 읽기 위치를 추적하고 동기화합니다. 수동 및 자동 옵션 포함. 새로운 게시물을 확인하면서 현재 위치를 잃지 않도록 이상적입니다.
// @icon              https://x.com/favicon.ico
// @namespace         http://tampermonkey.net/
// @version           2025-01-04
// @author            Copiis
// @license           MIT
// @match             https://x.com/home
// @grant             GM_setValue
// @grant             GM_getValue
// @grant             GM_download
// @downloadURL none
// ==/UserScript==
//                    If you find this script useful and would like to support my work, consider making a small donation!
//                    Bitcoin (BTC): bc1quc5mkudlwwkktzhvzw5u2nruxyepef957p68r7
//                    PayPal: https://www.paypal.com/paypalme/Coopiis?country.x=DE&locale.x=de_DE

(function() {
    'use strict';

    let lastReadPost = null;
    let isAutoScrolling = false;
    let isSearching = false;
    let isTabFocused = true;
    let downloadTriggered = false;

    // Internationalization
    const translations = {
        en: {
            scriptDisabled: "🚫 Script disabled: Not on the home page.",
            pageLoaded: "🚀 Page fully loaded. Initializing script...",
            tabBlur: "🌐 Tab lost focus.",
            downloadStart: "📥 Starting download of last read position...",
            alreadyDownloaded: "🗂️ Position already downloaded.",
            tabFocused: "🟢 Tab refocused.",
            saveSuccess: "✅ Last read position saved:",
            saveFail: "⚠️ No valid position to save.",
            noPostFound: "❌ No top visible post found.",
            highlightSuccess: "✅ Post highlighted successfully.",
            searchStart: "🔍 Refined search started...",
            searchCancel: "⏹️ Search manually canceled.",
        },
        de: {
            scriptDisabled: "🚫 Skript deaktiviert: Nicht auf der Home-Seite.",
            pageLoaded: "🚀 Seite vollständig geladen. Initialisiere Skript...",
            tabBlur: "🌐 Tab hat den Fokus verloren.",
            downloadStart: "📥 Starte Download der letzten Leseposition...",
            alreadyDownloaded: "🗂️ Leseposition bereits im Download-Ordner vorhanden.",
            tabFocused: "🟢 Tab wieder fokussiert.",
            saveSuccess: "✅ Leseposition erfolgreich gespeichert:",
            saveFail: "⚠️ Keine gültige Leseposition zum Speichern.",
            noPostFound: "❌ Kein oberster sichtbarer Beitrag gefunden.",
            highlightSuccess: "✅ Beitrag erfolgreich hervorgehoben.",
            searchStart: "🔍 Verfeinerte Suche gestartet...",
            searchCancel: "⏹️ Suche manuell abgebrochen.",
        }
    };

    const userLang = navigator.language.split('-')[0];
    const t = (key) => translations[userLang]?.[key] || translations.en[key];

    window.onload = async () => {
        if (!window.location.href.includes("/home")) {
            console.log(t("scriptDisabled"));
            return;
        }
        console.log(t("pageLoaded"));
        await loadNewestLastReadPost();
        await initializeScript();
        createButtons();
    };

    async function loadNewestLastReadPost() {
        try {
            const data = GM_getValue("lastReadPost", null);
            if (data) {
                lastReadPost = JSON.parse(data);
                console.log(t("saveSuccess"), lastReadPost);
            } else {
                console.warn(t("saveFail"));
            }
        } catch (err) {
            console.error("❌ Error loading last read post:", err);
        }
    }

    async function loadLastReadPostFromFile() {
        try {
            const data = GM_getValue("lastReadPost", null);
            if (data) {
                lastReadPost = JSON.parse(data);
                console.log(t("saveSuccess"), lastReadPost);
            } else {
                console.warn(t("saveFail"));
            }
        } catch (err) {
            console.error("❌ Error loading last read post from file:", err);
        }
    }

    window.addEventListener("blur", async () => {
        console.log(t("tabBlur"));
        if (lastReadPost && !downloadTriggered) {
            downloadTriggered = true;
            if (!(await isFileAlreadyDownloaded())) {
                console.log(t("downloadStart"));
                await downloadLastReadPost();
                await markDownloadAsComplete();
            } else {
                console.log(t("alreadyDownloaded"));
            }
            downloadTriggered = false;
        }
    });

    window.addEventListener("focus", () => {
        isTabFocused = true;
        downloadTriggered = false;
        console.log(t("tabFocused"));
    });

    async function initializeScript() {
        console.log(t("pageLoaded"));
        await loadLastReadPostFromFile();
        observeForNewPosts();

        window.addEventListener("scroll", () => {
            if (!isAutoScrolling && !isSearching) {
                markTopVisiblePost(true);
            }
        });
    }

    async function isFileAlreadyDownloaded() {
        const localFiles = await GM_getValue("downloadedPosts", []);
        const fileSignature = `${lastReadPost.authorHandler}_${lastReadPost.timestamp}`;
        return localFiles.includes(fileSignature);
    }

    async function markDownloadAsComplete() {
        const localFiles = await GM_getValue("downloadedPosts", []);
        const fileSignature = `${lastReadPost.authorHandler}_${lastReadPost.timestamp}`;
        if (!localFiles.includes(fileSignature)) {
            localFiles.push(fileSignature);
            GM_setValue("downloadedPosts", localFiles);
        }
    }

    async function downloadLastReadPost() {
        if (!lastReadPost || !lastReadPost.timestamp || !lastReadPost.authorHandler) {
            console.warn(t("saveFail"));
            return;
        }
        try {
            const data = JSON.stringify(lastReadPost, null, 2);
            const sanitizedHandler = lastReadPost.authorHandler.replace(/[^a-zA-Z0-9-_]/g, "");
            const timestamp = new Date(lastReadPost.timestamp).toISOString().replace(/[:.-]/g, "_");
            const fileName = `${sanitizedHandler}_${timestamp}.json`;

            GM_download({
                url: `data:application/json;charset=utf-8,${encodeURIComponent(data)}`,
                name: fileName,
                onload: () => console.log(`${t("saveSuccess")} ${fileName}`),
                onerror: (err) => console.error("❌ Error downloading:", err),
            });
        } catch (error) {
            console.error("❌ Download error:", error);
        }
    }

    function markTopVisiblePost(save = true) {
        const topPost = getTopVisiblePost();
        if (!topPost) {
            console.log(t("noPostFound"));
            return;
        }

        const postTimestamp = getPostTimestamp(topPost);
        const authorHandler = getPostAuthorHandler(topPost);

        if (postTimestamp && authorHandler) {
            if (save && (!lastReadPost || new Date(postTimestamp) > new Date(lastReadPost.timestamp))) {
                lastReadPost = { timestamp: postTimestamp, authorHandler };
                GM_setValue("lastReadPost", JSON.stringify(lastReadPost));
                console.log(t("saveSuccess"), lastReadPost);
            }
        }
    }

    function getTopVisiblePost() {
        const posts = Array.from(document.querySelectorAll("article"));
        return posts.find(post => {
            const rect = post.getBoundingClientRect();
            return rect.top >= 0 && rect.bottom > 0;
        });
    }

    function getPostTimestamp(post) {
        const timeElement = post.querySelector("time");
        return timeElement ? timeElement.getAttribute("datetime") : null;
    }

    function getPostAuthorHandler(post) {
        const handlerElement = post.querySelector('[role="link"][href*="/"]');
        return handlerElement ? handlerElement.getAttribute("href").slice(1) : null;
    }

    function startRefinedSearchForLastReadPost() {
        if (!lastReadPost || !lastReadPost.timestamp || !lastReadPost.authorHandler) {
            console.log("❌ No valid read position available. Search skipped.");
            return;
        }

        console.log(t("searchStart"));
        const popup = createSearchPopup();

        let direction = 1; // 1 = down, -1 = up
        let scrollAmount = 2000; // Initial scroll step
        let previousScrollY = -1;

        function handleSpaceKey(event) {
            if (event.code === "Space") {
                console.log(t("searchCancel"));
                isSearching = false;
                popup.remove();
                window.removeEventListener("keydown", handleSpaceKey);
            }
        }

        window.addEventListener("keydown", handleSpaceKey);

        const search = () => {
            if (!isSearching) {
                popup.remove();
                return;
            }

            const visiblePosts = getVisiblePosts();
            const comparison = compareVisiblePostsToLastReadPost(visiblePosts);

            if (comparison === "match") {
                const matchedPost = findPostByData(lastReadPost);
                if (matchedPost) {
                    console.log("🎯 Post found:", lastReadPost);
                    scrollToPostWithHighlight(matchedPost);
                    isSearching = false;
                    popup.remove();
                    window.removeEventListener("keydown", handleSpaceKey);
                    return;
                }
            } else if (comparison === "older") {
                direction = -1; // Scroll up
            } else if (comparison === "newer") {
                direction = 1; // Scroll down
            }

            if (window.scrollY === previousScrollY) {
                scrollAmount = Math.max(scrollAmount / 2, 500); // Halve step size on standstill
                direction = -direction; // Reverse direction
            } else {
                scrollAmount = Math.min(scrollAmount * 1.5, 3000); // Increase step size
            }

            previousScrollY = window.scrollY;

            window.scrollBy(0, direction * scrollAmount);

            setTimeout(search, 300);
        };

        isSearching = true;
        search();
    }

    function createSearchPopup() {
        const popup = document.createElement("div");
        popup.style.cssText = `
            position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);
            background: rgba(0, 0, 0, 0.9); color: #fff; padding: 10px 20px;
            border-radius: 8px; font-size: 14px; box-shadow: 0 0 10px rgba(255, 255, 255, 0.8);
            z-index: 10000;
        `;
        popup.textContent = "🔍 Refined search in progress... Press SPACE to cancel.";
        document.body.appendChild(popup);
        return popup;
    }

    function compareVisiblePostsToLastReadPost(posts) {
        const validPosts = posts.filter(post => post.timestamp && post.authorHandler);

        if (validPosts.length === 0) {
            console.log("⚠️ No visible posts found.");
            return null;
        }

        const lastReadTime = new Date(lastReadPost.timestamp);

        const allOlder = validPosts.every(post => new Date(post.timestamp) < lastReadTime);
        const allNewer = validPosts.every(post => new Date(post.timestamp) > lastReadTime);

        if (validPosts.some(post => post.timestamp === lastReadPost.timestamp && post.authorHandler === lastReadPost.authorHandler)) {
            return "match";
        } else if (allOlder) {
            return "older";
        } else if (allNewer) {
            return "newer";
        } else {
            return "mixed";
        }
    }

    function scrollToPostWithHighlight(post) {
        if (!post) {
            console.log("❌ No post to scroll to found.");
            return;
        }

        isAutoScrolling = true;

        post.style.cssText = `
            outline: none; box-shadow: 0 0 15px 5px rgba(255, 223, 0, 0.9);
            transition: box-shadow 1.5s ease-in-out, transform 0.3s ease; border-radius: 12px;
            transform: scale(1.02);
        `;

        post.scrollIntoView({ behavior: "smooth", block: "center" });

        setTimeout(() => {
            post.style.boxShadow = "0 0 0 0 rgba(255, 223, 0, 0)";
            post.style.transform = "scale(1)";
        }, 2000);

        setTimeout(() => {
            post.style.boxShadow = "none";
            post.style.borderRadius = "unset";
            isAutoScrolling = false;
            console.log(t("highlightSuccess"));
        }, 4500);
    }

    function getVisiblePosts() {
        const posts = Array.from(document.querySelectorAll("article"));
        return posts.map(post => ({
            element: post,
            timestamp: getPostTimestamp(post),
            authorHandler: getPostAuthorHandler(post),
        }));
    }

    function findPostByData(data) {
        const posts = Array.from(document.querySelectorAll("article"));
        return posts.find(post => {
            const postTimestamp = getPostTimestamp(post);
            const authorHandler = getPostAuthorHandler(post);
            return postTimestamp === data.timestamp && authorHandler === data.authorHandler;
        });
    }

    function createButtons() {
        const container = document.createElement("div");
        container.style.cssText = `
            position: fixed; top: 50%; left: 3px; transform: translateY(-50%);
            display: flex; flex-direction: column; gap: 3px; z-index: 10000;
        `;

        const buttons = [
            { icon: "📂", title: "Load saved reading position", onClick: importLastReadPost },
            { icon: "🔍", title: "Start manual search", onClick: startRefinedSearchForLastReadPost }
        ];

        buttons.forEach(({ icon, title, onClick }) => {
            const button = document.createElement("div");
            button.style.cssText = `
                width: 36px; height: 36px; background: rgba(0, 0, 0, 0.9); color: #fff;
                border-radius: 50%; display: flex; justify-content: center; align-items: center;
                cursor: pointer; font-size: 18px; box-shadow: inset 0 0 10px rgba(255, 255, 255, 0.5);
                transition: all 0.2s ease;
            `;
            button.title = title;
            button.textContent = icon;

            button.addEventListener("click", () => {
                button.style.boxShadow = "inset 0 0 20px rgba(255, 255, 255, 0.8)";
                button.style.transform = "scale(0.9)";
                setTimeout(() => {
                    button.style.boxShadow = "inset 0 0 10px rgba(255, 255, 255, 0.5)";
                    button.style.transform = "scale(1)";
                    onClick();
                }, 300);
            });

            ["mouseenter", "mouseleave"].forEach(event =>
                button.addEventListener(event, () => button.style.transform = event === "mouseenter" ? "scale(1.1)" : "scale(1)")
            );

            container.appendChild(button);
        });

        document.body.appendChild(container);
    }

    async function importLastReadPost() {
        const input = document.createElement("input");
        input.type = "file";
        input.accept = "application/json";
        input.style.display = "none";

        input.addEventListener("change", async (event) => {
            const file = event.target.files[0];
            if (file) {
                const reader = new FileReader();
                reader.onload = async () => {
                    try {
                        const importedData = JSON.parse(reader.result);
                        if (importedData.timestamp && importedData.authorHandler) {
                            lastReadPost = importedData;
                            await saveLastReadPostToFile();
                            showPopup("✅ Reading position loaded successfully. Starting refined search...");
                            console.log("✅ Imported reading position:", lastReadPost);
                            startRefinedSearchForLastReadPost();
                        } else {
                            throw new Error("Invalid reading position");
                        }
                    } catch (error) {
                        console.error("❌ Error importing reading position:", error);
                        showPopup("❌ Error: Invalid reading position.");
                    }
                };
                reader.readAsText(file);
            }
        });

        document.body.appendChild(input);
        input.click();
        document.body.removeChild(input);
    }

    function showPopup(message) {
        const popup = document.createElement("div");
        popup.style.cssText = `
            position: fixed; bottom: 20px; right: 20px;
            background: rgba(0, 0, 0, 0.9); color: #fff; padding: 10px 20px;
            border-radius: 8px; font-size: 14px; box-shadow: 0 0 10px rgba(255, 255, 255, 0.8);
            z-index: 10000;
        `;
        popup.textContent = message;
        document.body.appendChild(popup);
        setTimeout(() => popup.remove(), 3000);
    }

    function observeForNewPosts() {
        const targetNode = document.querySelector('div[aria-label="Timeline: Your Home Timeline"]') || document.body;
        const observer = new MutationObserver(mutations => {
            mutations.forEach(mutation => {
                if (mutation.type === 'childList' && window.scrollY <= 10) {
                    const newPostsIndicator = getNewPostsIndicator();
                    if (newPostsIndicator) {
                        console.log("🆕 New posts detected. Starting automatic search...");
                        clickNewPostsIndicator(newPostsIndicator);
                        setTimeout(() => startRefinedSearchForLastReadPost(), 1000);
                    }
                }
            });
        });

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

    function getNewPostsIndicator() {
        const buttons = document.querySelectorAll('button[role="button"]');
        for (const button of buttons) {
            const innerDiv = button.querySelector('div[style*="text-overflow: unset;"]');
            if (innerDiv) {
                const span = innerDiv.querySelector('span');
                if (span && /^\d+\s/.test(span.textContent.trim())) {
                    return button;
                }
            }
        }
        return null;
    }

    function clickNewPostsIndicator(indicator) {
        if (!indicator) return;
        indicator.scrollIntoView({ behavior: "smooth", block: "center" });
        setTimeout(() => indicator.click(), 500);
    }

    async function saveLastReadPostToFile() {
        try {
            if (!lastReadPost || !lastReadPost.timestamp || !lastReadPost.authorHandler) {
                console.warn("⚠️ No valid reading position available. Skipping save.");
                return;
            }

            // Retrieve current saved reading position
            const existingData = GM_getValue("lastReadPost", null);
            if (existingData) {
                const existingPost = JSON.parse(existingData);

                // Comparison: Is the new reading position really newer?
                if (
                    existingPost.timestamp === lastReadPost.timestamp &&
                    existingPost.authorHandler === lastReadPost.authorHandler
                ) {
                    console.log("⏹️ Reading position is identical to the saved one. No download needed.");
                    return;
                }

                // If the new position is older, don't overwrite
                if (new Date(existingPost.timestamp) > new Date(lastReadPost.timestamp)) {
                    console.log("⏹️ Saved reading position is newer. No download needed.");
                    return;
                }
            }

            // Save new reading position
            GM_setValue("lastReadPost", JSON.stringify(lastReadPost));
            console.log("💾 Reading position saved successfully:", lastReadPost);

            // Download new reading position
            await downloadLastReadPost();
        } catch (err) {
            console.error("❌ Error saving reading position:", err);
        }
    }
})();