task_manager.py

import json
import os
import datetime
import sys

TASKS_FILE = "tasks.json"

def load_tasks():
    #check if the file exists
    if not os.path.exists(TASKS_FILE):
        return []
    
    try:
        with open(TASKS_FILE, 'r') as f:
            tasks = json.load(f)
            return tasks
    except (json.JSONDecodeError, IOError):
        return []
    
def save_tasks(tasks):
    with open(TASKS_FILE, 'w') as f:
        json.dump(tasks, f, indent = 4)

#--------Task Functions---------

def get_next_id(tasks):
    if not tasks:
        return 1
    return max(task['id'] for task in tasks) + 1

def add_task(description):
    tasks = load_tasks()


    now = datetime.datetime.now().isoformat()

    new_task = {
        "id": get_next_id(tasks),
        "description": description,
        "status": "todo",
        "createdAt": now,
        "updatedAt": now
    }
    tasks.append(new_task)
    save_tasks(tasks)
    
    print(f"Success: Added new task (ID: {new_task['id']})")
    print(f"   Description: {description}")


def print_task(task):
    try:
        created_at = datetime.datetime.fromisoformat(task['createdAt']).strftime('%Y-%m-%d %H:%M')
        updated_at = datetime.datetime.fromisoformat(task['updatedAt']).strftime('%Y-%m-%d %H:%M')

    except ValueError:
        created_at = task['createdAt']
        updated_at = task['updatedAt']         

    print(f"\n ID: {task['id']}")
    print(f"  Description: {task['description']}")
    print(f"  Status: {task['status']}")
    print(f"  Created: {created_at}")
    print(f"  Updated: {updated_at}")
    print("-" * 20)


def list_tasks(status_filter = None):
    tasks = load_tasks()

    if not tasks:
        print("There are no tasks. Let's add one!")
        return
    
    valid_statuses = ["todo", "in-progress", "done", "not-done"]

    if status_filter:
        if status_filter not in valid_statuses:
            print(f"Invalid Status Filter : {status_filter}")
            print(f"Valid Filters are : 'todo' 'in-progress' 'done' 'not-done'")
            return
    
        filtered_tasks = []
        if status_filter == "not-done":
            filtered_tasks = [task for task in tasks if task['status'] in ("todo", "in-progress")]
        else:
            filtered_tasks = [task for task in tasks if task['status'] == status_filter]

        tasks_to_display = filtered_tasks
    else:
        tasks_to_display = tasks

    if not tasks_to_display:
        if status_filter:
            print(f" No tasks found with status: '{status_filter}'")
        return
    
    print(f"--- Showing {len(tasks_to_display)} Task(s) ---")
    for task in tasks_to_display:
        print_task(task)

def update_task_status(task_id_str, new_status):

    valid_statuses = ["todo", "in-progress", "done"]
    if new_status not in valid_statuses:
        print(f"Error: Invalid Status - '{new_status}'")
        print(f"Status must be 'todo', 'in-progress' or 'done'.")
        return
    
    try:
        task_id = int(task_id_str)
    except ValueError:
        print(f"Error: Invalid Task ID '{task_id_str}'. ID must be a number.")
        return
    
    tasks = load_tasks()
    task_found = False

    for task in tasks:
        if task['id'] == task_id:
            task['status'] = new_status
            task['updatedAt'] = datetime.datetime.now().isoformat()
            task_found = True
            break
    
    if task_found:
        save_tasks(tasks)
        print(f"Updated status for task {task_id} to '{new_status}'")
    else:
        print(f"Error: Task with ID {task_id} not found.")


def delete_task(task_id_str):
    try:
        task_id = int(task_id_str)
    except ValueError:
        print(f"Error: Invalid task ID '{task_id_str}'. ID must be a number.")
        return
    

    tasks = load_tasks()
    tasks_kept = [task for task in tasks if task['id'] != task_id]
    
    if len(tasks) == len(tasks_kept):
        print(f"Error: Task with ID {task_id} not found.")
    else:
        save_tasks(tasks_kept)
        print(f"Task Deleted! {task_id}.")

def update_task_description(task_id_str, new_description):
    if not new_description:
        print("Error: New Description cannot be empty.")
        return
    
    try:
        task_id = int(task_id_str)
    except ValueError:
        print(f"Error: Invalid task ID '{task_id_str}'. ID must be a number.")
        return
    
    tasks = load_tasks()
    task_found = False

    for task in tasks:
        if task['id'] == task_id:
            task['description'] = new_description
            task['updatedAt'] = datetime.datetime.now().isoformat()
            task_found = True
            break
    
    if task_found:
        save_tasks(tasks)
        print(f"Success: Updated task description for {task_id}.")
        print(f"New description: {new_description}")
    else:
        print(f"Task with ID '{task_id}' not found.")


#--------MAIN APP LOGIC---------

def print_usage():
    print("Usage - python task_manager.py <command> [arguements]")
    print("\nCommands")
    print("  add <description>     - Add a new task")
    print("  list [status]         - List all tasks or filter by status (todo, in-progress, done, not-done)")
    print("  status <id> <status>  - Update a task's status('todo', 'in-progress', 'done')")
    print("  delete <id>           - Delete a task by its ID")
    print("  update <id> <desc>    - Update a task's description")

def main():
    if len(sys.argv) < 2:
        print_usage()
        return
    
    command = sys.argv[1]

    if command == "add":
        if len(sys.argv) < 3:
            print("Error: Missing Task Description.")
            print("Usage: python task_manager.py add <description>")
            return
        

        description = " ".join(sys.argv[2:])
        add_task(description)


    elif command == "list":
        status_filter = None
        if len(sys.argv) > 2:
            status_filter = sys.argv[2]

        list_tasks(status_filter)

    elif command == "status":
        if len(sys.argv) < 4:
            print("Error: Missing arguments for 'status' command.")
            print("Usage: python_task_manager.py status <id> <status>")
            return
        
        task_id_str = sys.argv[2]
        new_status = sys.argv[3]
        update_task_status(task_id_str, new_status)

    elif command == "delete":
        if len(sys.argv) < 3:
            print("Error: Missing task ID.")
            print("Usage: python task_manager.py delete <id>")
            return
        
        task_id_str = sys.argv[2]
        delete_task(task_id_str)

    elif command == "update":
        if len(sys.argv) < 4:
            print("Error: Missing arguments for 'update' command.")
            print("Usage: python_task_manager.py update <id> <new description>")
            return
        
        task_id_str = sys.argv[2]
        new_description = " ".join(sys.argv[3:])
        update_task_description(task_id_str, new_description)

    else:
        print(f"Error: Unknown Command {command}")
        print_usage()


if __name__ == "__main__":
    main()