import json
import os
from typing import List, Optional
from app.models.schemas import User

DATA_DIR = "data"
USERS_FILE = os.path.join(DATA_DIR, "users.json")

class UserService:
    def __init__(self):
        if not os.path.exists(DATA_DIR):
            os.makedirs(DATA_DIR)
        self.users = self._load_users()
        
        # Ensure at least one admin user exists
        if not self.users:
            default_user = User(username="admin", password="admin")
            self.add_user(default_user)

    def _load_users(self) -> List[User]:
        if not os.path.exists(USERS_FILE):
            return []
        try:
            with open(USERS_FILE, "r") as f:
                data = json.load(f)
                return [User(**u) for u in data]
        except Exception:
            return []

    def _save_users(self):
        with open(USERS_FILE, "w") as f:
            json.dump([u.dict() for u in self.users], f, indent=4, default=str)

    def get_all_users(self) -> List[User]:
        return self.users

    def add_user(self, user: User) -> Optional[User]:
        if len(self.users) >= 10:
            return None
        # Avoid duplicate usernames
        if any(u.username == user.username for u in self.users):
            return None
        self.users.append(user)
        self._save_users()
        return user

    def delete_user(self, user_id: str) -> bool:
        # Don't allow deleting the last admin
        if len(self.users) <= 1:
            return False
        
        initial_len = len(self.users)
        self.users = [u for u in self.users if u.id != user_id]
        if len(self.users) < initial_len:
            self._save_users()
            return True
        return False

    def authenticate(self, username, password) -> Optional[User]:
        for user in self.users:
            if user.username == username and user.password == password:
                return user
        return None

user_service = UserService()