task_manager.py

#importing the json module
import json

#importing the os module
import os

#creating an empty list to store tasks
tasks = []

#constant for the filename where we save tasks
TASKS_FILE = "tasks.json"

def display_header():
    """Displays the header of the task manager."""
    print("="*40)
    print("        PERSONAL TASK MANAGER        ")
    print("="*40)

def display_menu():
    """Displays the main menu options."""
    print("\n--- Main Menu ---")
    print("1. Add a new task")
    print("2. View all tasks")
    print("3. Mark task as complete")
    print("4. Delete a task")
    print("5. Save and exit")
    print("-" * 20)

def add_task():
        """
        Add a new task to the task list.
        """
        description = input("Enter the task description: ")
        
        #Validate input and also strip whitespace
        if not description.strip():
            print("Task description cannot be empty.")
            return #break out of the function if input is valid
        
        task = {
            "description": description.strip(),
            "completed": False,   #New tasks start incomplete
            "id": len(tasks) + 1  #Assign a simple unique ID to each task 

        }

        #Append the new task to the tasks list
        tasks.append(task)

        #print confirmation message
        print(f"Task added successfully (ID: {task['id']})")

def view_tasks():
    """
    Displays all tasks in the task list, including the task ID, description, and status.
    """
    
    #Check if the tasks list is empty
    if not tasks:
        print("No tasks available.")
        return
    
    #Print header
    print("\n--- Your Tasks ---")

    #enumerate() to get index and task
    #we start index from 1 for user-friendliness
    for index, task in enumerate(tasks, start=1):
        #Get values from the task dictionary using the keys
        task_id = task["id"]
        description = task["description"]
        is_completed = task["completed"]

        # Ternary operator: value_if_true if condition else value_if_false
        status = "✓" if is_completed else " "
        print(f"{index}. [{status}] {description} (ID: {task_id})")

    #print summary
    #sum() adds up al the True values in the list (True counts as 1 and False as 0)
    completed_count = sum(task["completed"] for task in tasks)
    total_count = len(tasks)
    print(f"\nCompleted: {completed_count} / {total_count} tasks")

def mark_complete():
    """
    Mark a task as complete.
    User selects task by ID.
    """
    view_tasks()  #Show current tasks

    #if no tasks, return
    if not tasks:
        return
    
    #prompt user for task ID
    #Validate that input is a number
    try:
        task_id = int(input("\nEnter the ID of the task to mark as complete: "))
    except ValueError:
        print("Invalid input. Please enter a valid number")
        return
    
    #Find the task with the given ID
    for task in tasks:
        if task["id"] == task_id:
            #Found the task, mark it complete
            task["completed"] = True
            print(f"✓ {task_id} marked as complete.")
            return #Exit the function after marking complete
        
    print(f"No task found with ID: {task_id}")

def delete_task():
    """
    Delete a task from the task list.
    User selects task by ID.
    """
    view_tasks()  #Show current tasks

    #if no tasks, return
    if not tasks:
        return
    
    #prompt user for task ID
    #Validate that input is a number
    try:
        task_id = int(input("\nEnter the ID of the task to delete: "))
    except ValueError:
        print("Invalid input. Please enter a valid number")
        return
    
    #Find the task with the given ID and remove it
    for task in tasks:
        if task["id"] == task_id:
            tasks.remove(task)
            print(f"Task ID {task_id} deleted successfully.")
            return #Exit the function after deletion
        
    print(f"No task found with ID: {task_id}")

def save_tasks():
    """
    Save the current tasks to a JSON file.
    """
    with open(TASKS_FILE, "w") as file:
        json.dump(tasks, file, indent=2)

    print(f"Tasks saved to {TASKS_FILE} successfully.")

def load_tasks():
    """
    Load tasks from a JSON file.
    """
    #modifying the global tasks variable to update it
    global tasks

    #Check if the file exists before trying to open it
    if os.path.exists(TASKS_FILE):
        try:
            with open(TASKS_FILE, "r") as file:
                tasks = json.load(file)
            print(f" {len(tasks)} task(s)loaded from {TASKS_FILE} successfully.")
        except json.JSONDecodeError:
            print(f"Error: {TASKS_FILE} is corrupted or not in valid JSON format.")
            print("Starting afresh")
            tasks = []

    else: 
        #file does not exist
        print(f"No existing task file found. Starting with an empty task list.")


def main():
        """
        Main function to run the task manager.
        """
        display_header()
        load_tasks() #Load tasks at startup

        while True:
            display_menu()
            choice = input("Enter your choice (1-5): ")
            if choice == "1":
                add_task()
            elif choice == "2":
                view_tasks()
            elif choice == "3":
                mark_complete()
            elif choice == "4":
                delete_task()
            elif choice == "5":
                save_tasks()
                print("\nYour tasks have been saved. Goodbye!")
                break
            else:
                print("Invalid choice. Please enter a number between 1 and 5.")

if __name__ == "__main__":
    main()