const todoList = document.getElementById('todo-list');
const taskInput = document.getElementById('task-input');
const todoForm = document.getElementById('todo-form');

let tasks = [];

// --- Local Storage Management ---

function loadTasks() {
    // Attempt to retrieve tasks from localStorage
    const storedTasks = localStorage.getItem('todoTasks');
    if (storedTasks) {
        try {
            tasks = JSON.parse(storedTasks);
        } catch (e) {
            console.error("Error parsing tasks from localStorage:", e);
            tasks = [];
        }
    }
}

function saveTasks() {
    localStorage.setItem('todoTasks', JSON.stringify(tasks));
}

// --- Rendering ---

function renderTasks() {
    // Clear the current list content
    todoList.innerHTML = '';

    if (tasks.length === 0) {
        todoList.innerHTML = '<li class="empty-state">No tasks yet! Add one above.</li>';
        return;
    }

    // Use a DocumentFragment for performance when appending many nodes
    const fragment = document.createDocumentFragment();

    tasks.forEach((task, index) => {
        const listItem = document.createElement('li');
        listItem.classList.add('todo-item');
        listItem.setAttribute('aria-label', `Task: ${task.text}, ${task.completed ? 'Completed' : 'Pending'}`);
        
        if (task.completed) {
            listItem.classList.add('completed');
        }

        const taskContent = document.createElement('span');
        taskContent.classList.add('task-content');
        taskContent.textContent = task.text;
        taskContent.setAttribute('role', 'button');
        taskContent.setAttribute('tabindex', '0'); // Make span focusable
        
        // Event listener for toggling completion (Mark as Complete)
        taskContent.addEventListener('click', () => toggleComplete(index));
        taskContent.addEventListener('keydown', (e) => {
            if (e.key === 'Enter' || e.key === ' ') {
                e.preventDefault();
                toggleComplete(index);
            }
        });
        
        const deleteButton = document.createElement('button');
        deleteButton.classList.add('delete-btn');
        deleteButton.innerHTML = '&#10005;'; // X mark
        deleteButton.setAttribute('aria-label', `Delete task: ${task.text}`);
        
        // Event listener for deletion
        deleteButton.addEventListener('click', () => deleteTask(index));

        listItem.appendChild(taskContent);
        listItem.appendChild(deleteButton);
        fragment.appendChild(listItem);
    });
    
    todoList.appendChild(fragment);
}

// --- Core Functionality ---

function addTask(e) {
    e.preventDefault();
    const text = taskInput.value.trim();

    if (text) {
        const newTask = {
            id: Date.now(),
            text: text,
            completed: false
        };
        
        // Add new task to the beginning of the array
        tasks.unshift(newTask); 
        taskInput.value = '';
        
        saveTasks();
        renderTasks();
        
        // Announce the addition for screen readers (optional but good practice)
        // Note: Using aria-live="polite" on the UL generally handles this, 
        // but focusing the input might be enough feedback.
        taskInput.focus();
    }
}

function toggleComplete(index) {
    if (index >= 0 && index < tasks.length) {
        tasks[index].completed = !tasks[index].completed;
        saveTasks();
        renderTasks();
    }
}

function deleteTask(index) {
    if (index >= 0 && index < tasks.length) {
        const taskText = tasks[index].text;
        // Simple confirmation before deletion
        if (confirm(`Are you sure you want to delete "${taskText}"?`)) {
            tasks.splice(index, 1);
            saveTasks();
            renderTasks();
        }
    }
}

// --- Initialization ---

document.addEventListener('DOMContentLoaded', () => {
    loadTasks();
    renderTasks();
    
    // Setup event listener for the form submission
    todoForm.addEventListener('submit', addTask);
});