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

// Initialize todos from Local Storage, defaulting to an empty array
let todos = JSON.parse(localStorage.getItem('todos')) || [];

// Function to save todos to Local Storage
const saveTodos = () => {
    localStorage.setItem('todos', JSON.stringify(todos));
};

// Function to render the entire list
const renderTodos = () => {
    todoList.innerHTML = ''; // Clear existing list items

    if (todos.length === 0) {
        const emptyMessage = document.createElement('li');
        emptyMessage.textContent = "Great job! No tasks currently pending.";
        emptyMessage.className = "todo-item empty-state";
        todoList.appendChild(emptyMessage);
        return;
    }

    todos.forEach((todo, index) => {
        const listItem = document.createElement('li');
        listItem.className = `todo-item ${todo.completed ? 'completed' : ''}`;
        listItem.setAttribute('role', 'listitem');
        listItem.setAttribute('aria-checked', todo.completed);

        // Task Text (Clickable to toggle completion)
        const taskText = document.createElement('span');
        taskText.className = 'task-text';
        taskText.textContent = todo.text;
        taskText.setAttribute('tabindex', '0'); // Make text focusable for keyboard users
        taskText.addEventListener('click', () => toggleComplete(index));
        taskText.addEventListener('keydown', (e) => {
            if (e.key === 'Enter' || e.key === ' ') {
                e.preventDefault();
                toggleComplete(index);
            }
        });
        
        // Actions container
        const actions = document.createElement('div');
        actions.className = 'todo-actions';

        // Delete Button
        const deleteBtn = document.createElement('button');
        deleteBtn.textContent = 'Delete';
        deleteBtn.className = 'delete-btn';
        deleteBtn.setAttribute('aria-label', `Delete task: ${todo.text}`);
        deleteBtn.addEventListener('click', () => deleteTodo(index));

        listItem.appendChild(taskText);
        actions.appendChild(deleteBtn);
        listItem.appendChild(actions);

        todoList.appendChild(listItem);
    });
};

// 1. Add Functionality
const addTodo = (e) => {
    e.preventDefault();
    
    const taskText = todoInput.value.trim();
    
    if (taskText === "") {
        // Use standard constraint validation feedback if input is required, 
        // but since we prevent default and trim, a simple focus is enough
        alert("Please enter a task.");
        todoInput.focus();
        return;
    }

    const newTodo = {
        text: taskText,
        completed: false,
        id: Date.now() // Simple unique ID for future scalability if needed
    };

    todos.push(newTodo);
    saveTodos();
    renderTodos();

    todoInput.value = ''; // Clear input
    todoInput.focus();
};

// 2. Delete Functionality
const deleteTodo = (index) => {
    // Optional: add a visual confirmation dialog
    if (confirm(`Are you sure you want to delete "${todos[index].text}"?`)) {
        // Remove 1 element starting at the given index
        todos.splice(index, 1);
        saveTodos();
        renderTodos();
    }
};

// 3. Mark as Complete Functionality (Toggle)
const toggleComplete = (index) => {
    todos[index].completed = !todos[index].completed;
    saveTodos();
    renderTodos(); // Re-render to apply the completed class and ARIA state
};

// Event Listeners
document.addEventListener('DOMContentLoaded', renderTodos);
todoForm.addEventListener('submit', addTodo);