Python To-Do App – Task Manager

import json
from pathlib import Path
from datetime import datetime
from dataclasses import dataclass, asdict

TODO_FILE = Path("todos.json")

@dataclass
class Task:
    id: int
    title: str
    done: bool = False
    priority: str = "medium"
    created: str = ""
    def __post_init__(self):
        if not self.created:
            self.created = datetime.now().strftime("%Y-%m-%d %H:%M")

class TodoApp:
    def __init__(self):
        self.tasks: list[Task] = []
        self._next_id = 1
        self.load()

    def load(self):
        if TODO_FILE.exists():
            data = json.loads(TODO_FILE.read_text())
            self.tasks = [Task(**t) for t in data["tasks"]]
            self._next_id = data.get("next_id", len(self.tasks) + 1)

    def save(self):
        TODO_FILE.write_text(json.dumps(
            {"tasks": [asdict(t) for t in self.tasks], "next_id": self._next_id}, indent=2
        ))

    def add(self, title, priority="medium"):
        task = Task(id=self._next_id, title=title, priority=priority)
        self.tasks.append(task); self._next_id += 1; self.save(); return task

    def complete(self, task_id):
        task = next((t for t in self.tasks if t.id == task_id), None)
        if task: task.done = True; self.save()
        return task

    def delete(self, task_id):
        task = next((t for t in self.tasks if t.id == task_id), None)
        if task: self.tasks.remove(task); self.save(); return True
        return False

app = TodoApp()
ICONS = {"high": "🔴", "medium": "🟡", "low": "🟢"}

while True:
    print("\n[1]List [2]Add [3]Complete [4]Delete [q]Quit")
    c = input("> ").strip().lower()
    if c == "q": break
    elif c == "1":
        for t in sorted(app.tasks, key=lambda x: {"high":0,"medium":1,"low":2}[x.priority]):
            print(f"  [{t.id}] {'✓' if t.done else '○'} {ICONS[t.priority]} {t.title}")
    elif c == "2":
        title = input("Title: "); p = input("Priority [medium]: ") or "medium"
        task = app.add(title, p); print(f"Added #{task.id}")
    elif c == "3":
        tid = int(input("Task ID: "))
        print("Done!" if app.complete(tid) else "Not found.")
    elif c == "4":
        tid = int(input("Task ID: "))
        print("Deleted." if app.delete(tid) else "Not found.")