model.py

import os
import json

DATA_FILE = "tasks.json"

class TaskModel:
    def __init__(self):
        self.tasks = []
        self.load()
    
    def add_task(self, text, due_date=None, priority="Medium", category="Personal"):
        self.tasks.append({
            "text":     text, 
            "done":     False, 
            "due":      due_date, 
            "priority": priority, 
            "category": category
            })
        self.save()
    
    def toggle_task(self, index):
        self.tasks[index]["done"] = not self.tasks[index]["done"]
        self.save()
    
    def delete_task(self, index):
        del self.tasks[index]
        self.save()
    
    def sort_by_due(self):
        self.tasks.sort(key = lambda task: task.get("due") or "")
    
    def save(self):
        with open(DATA_FILE, "w") as f:
            json.dump(self.tasks, f)
    
    def load(self):
        if os.path.exists(DATA_FILE):
            with open(DATA_FILE, "r") as f:
                self.tasks = json.load(f)