from datetime import datetime, timedelta, timezone
from typing import Optional
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from passlib.context import CryptContext
from sqlalchemy.orm import Session

from . import crud, models, schemas
from .database import get_db
from .settings import settings

# Password Hashing
pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

# OAuth2 Scheme
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/token")

def verify_password(plain_password, hashed_password):
    return pwd_context.verify(plain_password, hashed_password)

def get_password_hash(password):
    return pwd_context.hash(password)

def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.now(timezone.utc) + expires_delta
    else:
        expire = datetime.now(timezone.utc) + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, settings.secret_key, algorithm=settings.algorithm)
    return encoded_jwt

def get_current_user(token: str = Depends(oauth2_scheme), db: Session = Depends(get_db)):
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    try:
        payload = jwt.decode(token, settings.secret_key, algorithms=[settings.algorithm])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = schemas.TokenData(username=username)
    except JWTError:
        raise credentials_exception
    user = crud.get_user_by_username(db, username=token_data.username)
    if user is None:
        raise credentials_exception
    return user

def get_current_active_teacher(current_user: models.User = Depends(get_current_user)):
    if current_user.role != models.UserRole.teacher:
        raise HTTPException(status_code=403, detail="Not authorized")
    return current_user