let tasks = [];

// Load tasks from local storage
window.onload = () => {
    const storedTasks = JSON.parse(localStorage.getItem("tasks"));
    if (storedTasks) {
        tasks = storedTasks;
        updateTaskList();
    }
};

function addTask() {
    const taskInput = document.getElementById("taskInput");
    const task = taskInput.value;
    if (task) {
        tasks.push({ text: task, completed: false }); // Store task object
        taskInput.value = ""; // Clear the input
        updateTaskList();
        saveTasksToLocalStorage(); // Save tasks
    } else {
        alert("Please enter a task.");
    }
}

function updateTaskList() {
    const taskList = document.getElementById("taskList");
    taskList.innerHTML = ""; // Clear current list
    tasks.forEach((task, index) => {
        const li = document.createElement("li");
        li.textContent = task.text;
        li.className = task.completed ? 'completed' : ''; // Add class if completed
        li.onclick = () => toggleTaskCompletion(index); // Toggle completion on click
        taskList.appendChild(li);
    });
}

function toggleTaskCompletion(index) {
    tasks[index].completed = !tasks[index].completed; // Toggle completion status
    updateTaskList();
    saveTasksToLocalStorage(); // Save tasks
}

function deleteTask(index) {
    tasks.splice(index, 1);
    updateTaskList();
    saveTasksToLocalStorage(); // Save tasks
}

function saveTasksToLocalStorage() {
    localStorage.setItem("tasks", JSON.stringify(tasks)); // Save tasks to local storage
}

function updateCountdown() {
    const examDate = new Date(document.getElementById("examDate").value);
    const today = new Date();
    const timeDiff = examDate - today;
    const daysLeft = Math.ceil(timeDiff / (1000 * 60 * 60 * 24));
    const countdown = document.getElementById("countdown");
    
    if (daysLeft >= 0) {
        countdown.textContent = `Days left until exam: ${daysLeft}`;
        notifyUser(`You have ${daysLeft} days left until your exam!`);
    } else {
        countdown.textContent = "Exam date has passed!";
    }
}

function notifyUser(message) {
    if (Notification.permission === "granted") {
        new Notification("Exam Reminder", {
            body: message,
        });
    } else if (Notification.permission !== "denied") {
        Notification.requestPermission().then(permission => {
            if (permission === "granted") {
                new Notification("Exam Reminder", {
                    body: message,
                });
            }
        });
    }
}

function showTimetable() {
    const timetableInput = document.getElementById("timetableInput").value;
    const timetableDisplay = document.getElementById("timetableDisplay");
    timetableDisplay.textContent = timetableInput.trim() || "No timetable entered.";
}

function toggleDarkMode() {
    document.body.classList.toggle("dark-mode");
}