todo_app.py

# ==========================================
# Python Learning Lab: CLI Todo List Application
# ==========================================
# This is a guided project. You will build a CLI application that:
# 1. Adds tasks to a list.
# 2. Views all active tasks.
# 3. Marks tasks as completed.
# 4. Saves tasks to a JSON file (`todo_list.json`) so they persist.
# 5. Loads tasks from the JSON file on startup.
#
# Instructions:
# - Fill in the # TODO placeholders.
# - Run the application: `python todo_app.py` and interact with the menu!

import os
import json

TODO_FILE = "todo_list.json"

def load_tasks():
    """Load tasks from the JSON database file. Return a list of dictionaries."""
    if not os.path.exists(TODO_FILE):
        return []
    
    # TODO: Open TODO_FILE in read mode, load JSON data, and return it.
    # Each task dictionary should look like: {"title": "Task Name", "completed": False}
    try:
        with open(TODO_FILE, "r") as f:
            return json.load(f)
    except Exception:
        return []

def save_tasks(tasks):
    """Save tasks list to the JSON database file."""
    # TODO: Open TODO_FILE in write mode and dump the tasks list using json.dump().
    with open(TODO_FILE, "w") as f:
        json.dump(tasks, f, indent=4)

def show_menu():
    print("\n--- CLI Todo List Manager ---")
    print("1. View Tasks")
    print("2. Add Task")
    print("3. Complete Task")
    print("4. Exit")

def view_tasks(tasks):
    if not tasks:
        print("\nNo tasks found! Add some tasks first.")
        return
    print("\n--- Current Tasks ---")
    for i, task in enumerate(tasks, 1):
        status = "✓" if task["completed"] else " "
        print(f"{i}. [{status}] {task['title']}")

def main():
    tasks = load_tasks()
    
    while True:
        show_menu()
        choice = input("\nEnter choice (1-4): ").strip()
        
        if choice == "1":
            view_tasks(tasks)
            
        elif choice == "2":
            title = input("Enter task description: ").strip()
            if title:
                # TODO: Append the new task as a dictionary to `tasks` and save the list
                new_task = {"title": title, "completed": False}
                tasks.append(new_task)
                save_tasks(tasks)
                print(f"Added task: '{title}'")
            else:
                print("Task title cannot be empty.")
                
        elif choice == "3":
            view_tasks(tasks)
            if not tasks:
                continue
            try:
                num = int(input("Enter task number to mark complete: ").strip())
                if 1 <= num <= len(tasks):
                    # TODO: Set the task's "completed" field to True, and save the list
                    tasks[num - 1]["completed"] = True
                    save_tasks(tasks)
                    print(f"Task {num} marked completed!")
                else:
                    print("Invalid task number.")
            except ValueError:
                print("Please enter a valid number.")
                
        elif choice == "4":
            print("\nGoodbye!")
            break
        else:
            print("Invalid selection. Please choose 1, 2, 3, or 4.")

if __name__ == "__main__":
    # If running interactively, call main()
    # To run test assertions in headless mode:
    # Set run_interactive to True to use CLI
    run_interactive = False
    
    if run_interactive:
        main()
    else:
        # Dry-run test assertions to check structure
        test_tasks = [{"title": "Learn OOP", "completed": False}]
        save_tasks(test_tasks)
        loaded = load_tasks()
        assert len(loaded) == 1, "Failed to load/save tasks"
        assert loaded[0]["title"] == "Learn OOP", "Task title did not match"
        
        # Cleanup
        if os.path.exists(TODO_FILE):
            os.remove(TODO_FILE)
        print("Todo App structure verified successfully! Switch 'run_interactive' to True to play with it!")