let user = null;
const $ = id => document.getElementById(id);

// DATA STORAGE
const db = {
    getUsers: () => JSON.parse(localStorage.getItem('users')) || [{ username: 'admin', email: 'admin@library.com', password: 'admin123', fullname: 'Administrator', isAdmin: true }],
    saveUsers: u => localStorage.setItem('users', JSON.stringify(u)),
    getBooks: () => JSON.parse(localStorage.getItem('books')) || [
        { id: 1, title: 'To Kill a Mockingbird', author: 'Harper Lee', genre: 'Fiction', quantity: 3, borrowedBy: [] },
        { id: 2, title: '1984', author: 'George Orwell', genre: 'Dystopian', quantity: 2, borrowedBy: [] },
        { id: 3, title: 'Pride and Prejudice', author: 'Jane Austen', genre: 'Romance', quantity: 2, borrowedBy: [] },
        { id: 4, title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', genre: 'Classic', quantity: 3, borrowedBy: [] },
        { id: 5, title: 'The Hobbit', author: 'J. R. R. Tolkien', genre: 'Fantasy', quantity: 2, borrowedBy: [] },
        { id: 6, title: 'The Catcher in the Rye', author: 'J. D. Salinger', genre: 'Fiction', quantity: 2, borrowedBy: [] },
        { id: 7, title: 'The Alchemist', author: 'Paulo Coelho', genre: 'Adventure', quantity: 2, borrowedBy: [] },
        { id: 8, title: 'Harry Potter and the Sorcerer\'s Stone', author: 'J. K. Rowling', genre: 'Fantasy', quantity: 4, borrowedBy: [] },
        { id: 9, title: 'The Lord of the Rings', author: 'J. R. R. Tolkien', genre: 'Fantasy', quantity: 2, borrowedBy: [] },
        { id: 10, title: 'The Hunger Games', author: 'Suzanne Collins', genre: 'Dystopian', quantity: 3, borrowedBy: [] },
        { id: 11, title: 'The Book Thief', author: 'Markus Zusak', genre: 'Historical Fiction', quantity: 2, borrowedBy: [] },
        { id: 12, title: 'The Chronicles of Narnia', author: 'C. S. Lewis', genre: 'Fantasy', quantity: 2, borrowedBy: [] },
        { id: 13, title: 'Brave New World', author: 'Aldous Huxley', genre: 'Dystopian', quantity: 2, borrowedBy: [] },
        { id: 14, title: 'The Fault in Our Stars', author: 'John Green', genre: 'Romance', quantity: 3, borrowedBy: [] },
        { id: 15, title: 'The Da Vinci Code', author: 'Dan Brown', genre: 'Mystery', quantity: 2, borrowedBy: [] },
        { id: 16, title: 'The Shining', author: 'Stephen King', genre: 'Horror', quantity: 2, borrowedBy: [] },
        { id: 17, title: 'The Girl with the Dragon Tattoo', author: 'Stieg Larsson', genre: 'Crime', quantity: 2, borrowedBy: [] },
        { id: 18, title: 'Moby-Dick', author: 'Herman Melville', genre: 'Adventure', quantity: 1, borrowedBy: [] },
        { id: 19, title: 'The Road', author: 'Cormac McCarthy', genre: 'Post-Apocalyptic', quantity: 2, borrowedBy: [] },
        { id: 20, title: 'Jane Eyre', author: 'Charlotte Brontë', genre: 'Romance', quantity: 2, borrowedBy: [] }
    ],
    saveBooks: b => localStorage.setItem('books', JSON.stringify(b)),
    getHistory: () => JSON.parse(localStorage.getItem('history')) || [],
    saveHistory: h => localStorage.setItem('history', JSON.stringify(h))
};

// HELPERS
const getUser = n => db.getUsers().find(u => u.username === n);
const addHistory = (id, title, action, details) => {
    const h = db.getHistory();
    h.push({ id: Date.now(), username: user.username, bookId: id, bookTitle: title, action, timestamp: new Date().toISOString(), ...details });
    db.saveHistory(h);
};
const getBorrowed = b => b.borrowedBy.filter(x => !x.returnDate).length;
const getAvailable = b => b.quantity - getBorrowed(b);
const formatDate = d => new Date(d).toLocaleDateString();
const userRecord = (b, u) => b.borrowedBy.find(x => x.user === u && !x.returnDate);

// INIT
window.addEventListener('DOMContentLoaded', () => {
    // Clear old data with ISBN and reset to new format with genres
    const oldBooks = JSON.parse(localStorage.getItem('books') || '[]');
    if (oldBooks.length > 0 && oldBooks[0].isbn) {
        localStorage.removeItem('books');
        localStorage.removeItem('history');
    }
    
    user = localStorage.getItem('currentUser') ? getUser(localStorage.getItem('currentUser')) : { username: 'guest', fullname: 'Gast', isAdmin: false };
    $('welcome-sidebar').innerText = user.fullname;
    if (user.isAdmin) $('tab-admin').style.display = 'flex';
    switchTab('dashboard');
});

// AUTHEN
const handleRegister = () => {
    const [u, e, p, f] = [$('register-username').value, $('register-email').value, $('register-password').value, $('register-fullname').value].map(x => x.trim());
    if (!u || !e || !p || !f) return alert('Bitte alle Felder ausfüllen');
    if (getUser(u)) return alert('Benutzer existiert bereits');
    db.getUsers().push({ username: u, email: e, password: p, fullname: f, isAdmin: false, registeredDate: new Date().toISOString() });
    db.saveUsers(db.getUsers());
    alert('Erfolg! Du kannst dich jetzt anmelden.');
    toggleAuthForm();
    [$('register-username'), $('register-email'), $('register-password'), $('register-fullname')].forEach(x => x.value = '');
};

const handleLogin = () => {
    const [u, p] = [$('login-username').value.trim(), $('login-password').value.trim()];
    if (!u || !p) return alert('Bitte Anmeldedaten eingeben');
    const userData = getUser(u);
    if (!userData || userData.password !== p) return alert('Ungültige Anmeldedaten');
    user = userData;
    localStorage.setItem('currentUser', u);
    $('login-username').value = '';
    $('login-password').value = '';
    $('auth-section').classList.add('hidden');
    $('welcome-sidebar').innerText = user.fullname;
    if (user.isAdmin) $('tab-admin').style.display = 'flex';
    switchTab('dashboard');
};

const logout = () => {
    localStorage.removeItem('currentUser');
    user = { username: 'guest', fullname: 'Gast', isAdmin: false };
    $('welcome-sidebar').innerText = 'Gast';
    $('tab-admin').style.display = 'none';
    $('auth-section').classList.remove('hidden');
    switchTab('dashboard');
};

const toggleAuthForm = () => {
    $('login-form').classList.toggle('hidden');
    $('register-form').classList.toggle('hidden');
};

// BOOKS
const borrowBook = bid => {
    const books = db.getBooks();
    const book = books.find(b => b.id === bid);
    if (!book || userRecord(book, user.username) || getAvailable(book) <= 0) return alert('Kann nicht ausgeliehen werden');
    const due = new Date();
    due.setDate(due.getDate() + 14);
    book.borrowedBy.push({ user: user.username, borrowDate: new Date().toISOString(), dueDate: due.toISOString(), returnDate: null });
    db.saveBooks(books);
    addHistory(book.id, book.title, 'BORROWED', { dueDate: due.toISOString() });
    render();
};

const returnBook = bid => {
    const books = db.getBooks();
    const book = books.find(b => b.id === bid);
    const record = userRecord(book, user.username);
    if (!record) return alert('Nicht ausgeliehen');
    record.returnDate = new Date().toISOString();
    db.saveBooks(books);
    addHistory(book.id, book.title, 'RETURNED');
    render();
};

const addBookAdmin = () => {
    const [t, a, g, q] = [$('admin-title').value.trim(), $('admin-author').value.trim(), $('admin-genre').value.trim(), parseInt($('admin-quantity').value) || 1];
    if (!t || !a || !g) return alert('Bitte alle Felder ausfüllen');
    const books = db.getBooks();
    const existing = books.find(b => b.title === t);
    if (existing) existing.quantity += q;
    else books.push({ id: Date.now(), title: t, author: a, genre: g, quantity: q, borrowedBy: [] });
    db.saveBooks(books);
    [$('admin-title'), $('admin-author'), $('admin-genre'), $('admin-quantity')].forEach(x => x.value = x === $('admin-quantity') ? '1' : '');
    renderAdminBooks();
};

// UI
const switchTab = t => {
    document.querySelectorAll('.tab-content').forEach(el => el.classList.add('hidden'));
    document.querySelectorAll('.nav-item').forEach(el => el.classList.remove('active'));
    $(t + '-tab').classList.remove('hidden');
    $('tab-' + t).classList.add('active');
    if (t === 'books') populateGenreFilter();
    ({ books: renderBooks, 'my-books': renderMyBooks, history: renderHistory, admin: renderAdminBooks, dashboard: updateDashboard }[t] || (() => {}))();
};

const updateDashboard = () => {
    const newsItems = [
        { id: 1, title: 'Neuerscheinung: Die Mitternachtsbibliothek', subtitle: 'Matt Haig', desc: 'Eine fesselnde moderne Fantasy über die Entscheidungen, die wir nie getroffen haben. Jetzt verfügbar!' },
        { id: 2, title: 'Autogrammstunde', subtitle: 'Brandon Sanderson Tour 2024', desc: 'Nimm teil an einer exklusiven Signierstunde mit Bestsellerautor Brandon Sanderson am 15. März um 18 Uhr.' },
        { id: 3, title: 'Neuerscheinung', subtitle: 'Project Hail Mary - Andy Weir', desc: 'Erscheint am 28. Februar! Jetzt vorbestellen für dieses epische Sci-Fi-Abenteuer.' },
        { id: 4, title: 'Neu im Bestand: Fourth Wing', subtitle: 'Rebecca Yarros', desc: 'Drachenreiter, Magie und epische Romantik. Diese Fantasy-Sensation jetzt in unserer Sammlung!' },
        { id: 5, title: 'Autoren-Spotlight', subtitle: 'Colleen Hoover Kollektion', desc: 'Wir haben unseren Romance-Bereich um die vollständigen Werke von Colleen Hoover erweitert.' },
        { id: 6, title: 'Lese-Challenge 2024', subtitle: 'Mach mit in der Community', desc: 'Lies 12 Bücher in diesem Jahr! Gewinne exklusive Lesezeichen und Bibliotheks-Preise.' },
        { id: 7, title: 'Valentinstag-Special', subtitle: 'Romantische Bücher', desc: 'Entdecke unsere Auswahl an Liebesromanen und erhalte 20% Rabatt, wenn du 3 oder mehr ausleihst!' },
        { id: 8, title: 'Beliebt jetzt', subtitle: 'Verity von Colleen Hoover', desc: 'Der meistgelesene Thriller, den Leser nicht aus der Hand legen können. Nur begrenzt verfügbar!' }
    ];

    const persistedIds = JSON.parse(localStorage.getItem('newsItemsOrder') || 'null');
    const selectedIds = Array.isArray(persistedIds) && persistedIds.length ? persistedIds : newsItems.slice(0, 6).map(i => i.id);

    if (!persistedIds) {
        localStorage.setItem('newsItemsOrder', JSON.stringify(selectedIds));
    }

    const news = selectedIds.map(id => newsItems.find(i => i.id === id)).filter(Boolean);
    $('news-container').innerHTML = news.map(n => `<div class="news-card"><h3>${n.title}</h3><p class="news-subtitle">${n.subtitle}</p><p class="news-desc">${n.desc}</p></div>`).join('');
};

const renderBooks = () => {
    const books = db.getBooks();
    const [s, st, g] = [$('search-books').value.toLowerCase(), $('filter-status').value, $('filter-genre').value];
    const filtered = books.filter(b => (b.title.toLowerCase().includes(s) || b.author.toLowerCase().includes(s)) && (!g || b.genre === g) && (st === 'all' || (st === 'available' && getAvailable(b) > 0) || (st === 'borrowed' && getAvailable(b) === 0)));
    $('book-list').innerHTML = filtered.map(b => {
        const avail = getAvailable(b);
        const rec = userRecord(b, user.username);
        return `<div class="book-card ${avail > 0 ? 'available' : 'unavailable'}">
            <h3>${b.title}</h3><p><strong>Autor:</strong> ${b.author}</p>
            <p><strong>Genre:</strong> ${b.genre}</p><p class="copies-badge">Verfügbar: ${avail}/${b.quantity}</p>
            <div class="book-actions">${rec ? `<p class="due-date ${new Date(rec.dueDate) < new Date() ? 'overdue' : ''}">Fällig: ${formatDate(rec.dueDate)}</p><button onclick="returnBook(${b.id})" class="btn-return">Zurückgeben</button>` : (avail > 0 ? `<button onclick="borrowBook(${b.id})" class="btn-borrow">Ausleihen</button>` : '')}</div>
        </div>`;
    }).join('');
};

const renderMyBooks = () => {
    const books = db.getBooks().filter(b => userRecord(b, user.username)).map(b => ({ ...b, record: userRecord(b, user.username) }));
    $('my-books-list').innerHTML = books.length === 0 ? '<p class="empty-message">Keine ausgeliehenen Bücher</p>' : books.map(b => {
        const overdue = new Date(b.record.dueDate) < new Date();
        return `<div class="book-card ${overdue ? 'overdue' : 'ontime'}">
            <h3>${b.title}</h3><p><strong>Autor:</strong> ${b.author}</p>
            <p><strong>Ausgeliehen:</strong> ${formatDate(b.record.borrowDate)}</p>
            <p class="due-date ${overdue ? 'overdue' : ''}">Fällig: ${formatDate(b.record.dueDate)}</p>
            ${overdue ? '<p style="background:red;color:white;padding:8px;border-radius:4px;font-weight:600;">ÜBERFÄLLIG</p>' : ''}
            <button onclick="returnBook(${b.id})" class="btn-return">Zurückgeben</button>
        </div>`;
    }).join('');
};

const renderHistory = () => {
    const hist = db.getHistory().filter(h => h.username === user.username);
    const filtered = $('history-filter').value === 'all' ? hist : hist.filter(h => h.action === $('history-filter').value.toUpperCase());
    $('history-list').innerHTML = filtered.length === 0 ? '<p class="empty-message">Kein Verlauf</p>' : 
        `<table class="history-table-content"><tr><th>Datum</th><th>Titel</th><th>Aktion</th><th>Fällig</th></tr>${filtered.reverse().map(e => `<tr><td>${formatDate(e.timestamp)}</td><td>${e.bookTitle}</td><td>${e.action === 'BORROWED' ? 'Ausgeliehen' : 'Zurückgegeben'}</td><td>${e.dueDate ? formatDate(e.dueDate) : '-'}</td></tr>`).join('')}</table>`;
};

const clearHistory = () => {
    if (!confirm('Verlauf löschen? Dies kann nicht rückgängig gemacht werden.')) return;
    const updated = db.getHistory().filter(h => h.username !== user.username);
    db.saveHistory(updated);
    renderHistory();
};

const renderAdminBooks = () => {
    const books = db.getBooks();
    $('admin-book-list').innerHTML = books.map(b => {
        const borrowed = getBorrowed(b);
        const details = b.borrowedBy.filter(x => !x.returnDate).map(x => `<p>${x.user} (${formatDate(x.dueDate)}) ${new Date(x.dueDate) < new Date() ? 'ÜBERFÄLLIG' : ''}</p>`).join('');
        return `<div class="book-card admin-card">
            <h3>${b.title}</h3><p><strong>Autor:</strong> ${b.author}</p>
            <p><strong>Genre:</strong> ${b.genre}</p><p><strong>Gesamt:</strong> ${b.quantity} | <strong>Verfügbar:</strong> ${getAvailable(b)} | <strong>Ausgeliehen:</strong> ${borrowed}</p>
            ${details ? `<div class="borrow-details">${details}</div>` : ''}
        </div>`;
    }).join('');
};

const populateGenreFilter = () => {
    const genres = [...new Set(db.getBooks().map(b => b.genre))].sort();
    $('filter-genre').innerHTML = '<option value="">Alle Genres</option>' + genres.map(g => `<option value="${g}">${g}</option>`).join('');
};

const render = () => {
    renderBooks();
    renderMyBooks();
    updateDashboard();
    updateFloatingTimer();
};

const updateFloatingTimer = () => {
    const books = db.getBooks();
    let soonest = null;

    books.forEach(b => {
        const rec = userRecord(b, user.username);
        if (rec) {
            const due = new Date(rec.dueDate).getTime();
            if (!soonest || due < soonest.due) {
                soonest = {
                    due: due,
                    start: new Date(rec.borrowDate).getTime(),
                    title: b.title
                };
            }
        }
    });

    const timerText = document.getElementById('timer-text');
    const timerProgress = document.getElementById('timer-progress');
    if (!timerText || !timerProgress) return;

    if (!soonest) {
        timerText.innerText = 'Keine ausgeliehenen Bücher';
        timerProgress.style.width = '0%';
        return;
    }

    const now = Date.now();
    const percent = ((now - soonest.start) / (soonest.due - soonest.start)) * 100;
    const remaining = soonest.due - now;
    const days = Math.ceil(remaining / (1000 * 60 * 60 * 24));

    timerText.innerText = `${soonest.title} fällig in ${days} Tagen`;
    timerProgress.style.width = Math.min(100, Math.max(0, percent)) + '%';
};

setInterval(updateFloatingTimer, 60000);
updateFloatingTimer();