import os
import json

FILE_NAME = "tasks.json"
tasks = []

def load_tasks():
    """Attempts to load tasks from the JSON file if it exists."""
    global tasks
    if os.path.exists(FILE_NAME):
        try:
            with open(FILE_NAME, 'r') as file:
                tasks = json.load(file)
            print(f"✅ Tasks successfully loaded from {FILE_NAME}.")
        except Exception as e:
            print(f"❌ Error loading tasks: {e}")
            tasks = []
    else:
        print(f"📄 No previous task file ({FILE_NAME}) found. Starting with an empty list.")

def save_tasks():
    """Saves the current list of tasks to the JSON file."""
    try:
        with open(FILE_NAME, 'w') as file:
            json.dump(tasks, file, indent=4)
        print(f"✅ Tasks successfully saved to {FILE_NAME}.")
    except Exception as e:
        print(f"❌ Error saving tasks: {e}")

def add_task(task_description):
    """Adds a new task to the list with a 'completed' status."""
    tasks.append({"task": task_description, "completed": False})
    print(f"✨ Task added: '{task_description}'")

def view_tasks():
    """Displays all tasks with their index and status."""
    if not tasks:
        print("
📝 Your To-Do List is empty. Time to add a task!")
        return
    print("
--- Current To-Do List ---")
    for index, task in enumerate(tasks, start=1):
        status = "✅" if task["completed"] else "❌"
        print(f"{index}. [{status}] {task['task']}")
    print("--------------------------")

def delete_task(task_number):
    """Deletes a task based on its number (index + 1)."""
    try:
        task_index = int(task_number) - 1
        if 0 <= task_index < len(tasks):
            deleted_task = tasks.pop(task_index)
            print(f"🗑️ Deleted task: '{deleted_task['task']}'")
        else:
            print("❌ Invalid task number. Please try again.")
    except ValueError:
        print("❌ Invalid input. Please enter a number.")

def mark_completed(task_number):
    """Marks a task as completed based on its number (index + 1)."""
    try:
        task_index = int(task_number) - 1
        if 0 <= task_index < len(tasks):
            tasks[task_index]["completed"] = True
            print(f"🎉 Marked as completed: '{tasks[task_index]['task']}'")
        else:
            print("❌ Invalid task number. Please try again.")
    except ValueError:
        print("❌ Invalid input. Please enter a number.")

def main_menu():
    """Displays the main menu and handles user choices."""
    load_tasks()
    while True:
        view_tasks()
        print("
--- COMMANDS ---")
        print("1: Add a new task")
        print("2: Delete a task (by number)")
        print("3: Mark a task as completed (by number)")
        print("4: Save & Exit")
        print("----------------")
        choice = input("Select a command (1-4): ")
        if choice == '1':
            task_desc = input("Enter the task description: ")
            if task_desc:
                add_task(task_desc)
            else:
                print("Task description cannot be empty.")
        elif choice == '2':
            task_num = input("Enter the number of the task to delete: ")
            delete_task(task_num)
        elif choice == '3':
            task_num = input("Enter the number of the task to mark as completed: ")
            mark_completed(task_num)
        elif choice == '4':
            save_tasks()
            print("👋 System shutting down. Goodbye!")
            break
        else:
            print("❌ Invalid choice. Please select a number from 1 to 4.")

if __name__ == "__main__":
    main_menu()