script.js

// Класс LibrarySystem (модель DFD)
class LibrarySystem {
    constructor() {
        this.books = [];
        // Начальные данные
        this.addBook("Война и мир", "Лев Толстой", 1869);
        this.addBook("Преступление и наказание", "Фёдор Достоевский", 1866);
        this.addBook("Мастер и Маргарита", "Михаил Булгаков", 1967);
    }

    addBook(title, author, year) {
        if (!title || !author || !year) return false;
        const book = {
            id: Date.now() + Math.random(),
            title: title.trim(),
            author: author.trim(),
            year: parseInt(year),
            available: true
        };
        this.books.push(book);
        return true;
    }

    findBook(title) {
        if (!title) return null;
        return this.books.find(book => book.title.toLowerCase() === title.trim().toLowerCase()) || null;
    }

    issueBook(title) {
        const book = this.findBook(title);
        if (!book) return { success: false, message: `Книга "${title}" не найдена.` };
        if (!book.available) return { success: false, message: `Книга "${title}" уже выдана.` };
        book.available = false;
        return { success: true, message: `Книга "${title}" выдана читателю.` };
    }

    returnBook(title) {
        const book = this.findBook(title);
        if (!book) return { success: false, message: `Книга "${title}" не найдена.` };
        if (book.available) return { success: false, message: `Книга "${title}" уже доступна.` };
        book.available = true;
        return { success: true, message: `Книга "${title}" возвращена в библиотеку.` };
    }

    getAllBooks() {
        return [...this.books];
    }
}

// Инициализация
const library = new LibrarySystem();

// DOM элементы
const booksContainer = document.getElementById('booksContainer');
const addBookBtn = document.getElementById('addBookBtn');
const searchBookBtn = document.getElementById('searchBookBtn');
const issueBookBtn = document.getElementById('issueBookBtn');
const returnBookBtn = document.getElementById('returnBookBtn');
const addMessage = document.getElementById('addMessage');
const searchResult = document.getElementById('searchResult');
const actionMessage = document.getElementById('actionMessage');

// Утилиты
function escapeHtml(str) {
    if (!str) return '';
    return str.replace(/[&<>]/g, function(m) {
        if (m === '&') return '&amp;';
        if (m === '<') return '&lt;';
        if (m === '>') return '&gt;';
        return m;
    });
}

function showMessage(element, text, isSuccess) {
    element.textContent = text;
    element.className = `message ${isSuccess ? 'success' : 'error'}`;
    setTimeout(() => {
        element.textContent = '';
        element.className = 'message';
    }, 3000);
}

// Рендер всех книг
function renderBooks() {
    const books = library.getAllBooks();
    if (books.length === 0) {
        booksContainer.innerHTML = '<p class="empty-message">Фонд пуст. Добавьте первую книгу.</p>';
        return;
    }

    let html = '';
    books.forEach(book => {
        const statusClass = book.available ? 'available' : 'issued';
        const statusText = book.available ? 'Доступна' : 'Выдана';
        html += `
            <div class="book-item">
                <div class="book-info">
                    <div class="book-title">
                        ${escapeHtml(book.title)}
                        <span class="status ${statusClass}">${statusText}</span>
                    </div>
                    <div class="book-details">${escapeHtml(book.author)} • ${book.year} г.</div>
                </div>
                <div class="book-actions">
                    <button onclick="window.quickIssue('${escapeHtml(book.title).replace(/'/g, "\\'")}')" 
                        ${!book.available ? 'disabled' : ''} class="btn-warning small">Выдать</button>
                    <button onclick="window.quickReturn('${escapeHtml(book.title).replace(/'/g, "\\'")}')" 
                        ${book.available ? 'disabled' : ''} class="btn-success small">Вернуть</button>
                </div>
            </div>
        `;
    });
    booksContainer.innerHTML = html;
}

// Быстрые действия
window.quickIssue = function(title) {
    const result = library.issueBook(title);
    showMessage(actionMessage, result.message, result.success);
    renderBooks();
    const searchInput = document.getElementById('searchTitle');
    if (searchInput.value.trim()) performSearch();
};

window.quickReturn = function(title) {
    const result = library.returnBook(title);
    showMessage(actionMessage, result.message, result.success);
    renderBooks();
    const searchInput = document.getElementById('searchTitle');
    if (searchInput.value.trim()) performSearch();
};

// Поиск
function performSearch() {
    const title = document.getElementById('searchTitle').value;
    if (!title.trim()) {
        searchResult.innerHTML = '<em>Введите название для поиска.</em>';
        return;
    }
    const book = library.findBook(title);
    if (book) {
        const status = book.available ? 'Доступна' : 'Выдана';
        searchResult.innerHTML = `
            <strong>📘 Найдено:</strong><br>
            <strong>${escapeHtml(book.title)}</strong><br>
            ${escapeHtml(book.author)} (${book.year})<br>
            <span class="status ${book.available ? 'available' : 'issued'}">${status}</span>
        `;
    } else {
        searchResult.innerHTML = '<em>❌ Книга не найдена.</em>';
    }
}

// Добавление книги
addBookBtn.addEventListener('click', () => {
    const title = document.getElementById('bookTitle').value;
    const author = document.getElementById('bookAuthor').value;
    const year = document.getElementById('bookYear').value;
    if (!title || !author || !year) {
        showMessage(addMessage, 'Заполните все поля!', false);
        return;
    }
    const success = library.addBook(title, author, year);
    if (success) {
        showMessage(addMessage, `Книга "${title}" успешно добавлена.`, true);
        document.getElementById('bookTitle').value = '';
        document.getElementById('bookAuthor').value = '';
        document.getElementById('bookYear').value = '';
        renderBooks();
        const searchInput = document.getElementById('searchTitle');
        if (searchInput.value.trim()) performSearch();
    } else {
        showMessage(addMessage, 'Ошибка добавления книги.', false);
    }
});

// Поиск (кнопка и Enter)
searchBookBtn.addEventListener('click', performSearch);
document.getElementById('searchTitle').addEventListener('keypress', (e) => {
    if (e.key === 'Enter') performSearch();
});

// Выдача
issueBookBtn.addEventListener('click', () => {
    const title = document.getElementById('actionTitle').value;
    if (!title.trim()) {
        showMessage(actionMessage, 'Введите название книги.', false);
        return;
    }
    const result = library.issueBook(title);
    showMessage(actionMessage, result.message, result.success);
    if (result.success) {
        document.getElementById('actionTitle').value = '';
        renderBooks();
        const searchInput = document.getElementById('searchTitle');
        if (searchInput.value.trim()) performSearch();
    }
});

// Возврат
returnBookBtn.addEventListener('click', () => {
    const title = document.getElementById('actionTitle').value;
    if (!title.trim()) {
        showMessage(actionMessage, 'Введите название книги.', false);
        return;
    }
    const result = library.returnBook(title);
    showMessage(actionMessage, result.message, result.success);
    if (result.success) {
        document.getElementById('actionTitle').value = '';
        renderBooks();
        const searchInput = document.getElementById('searchTitle');
        if (searchInput.value.trim()) performSearch();
    }
});

// Первоначальный рендер
renderBooks();