from datetime import datetime, timedelta, timezone

import bcrypt
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from sqlalchemy.orm import Session

from app import crud, models
from app.config import settings
from app.database import get_db
from app.schemas import TokenData


oauth2_scheme = OAuth2PasswordBearer(tokenUrl="api/auth/token")  # tokenUrl points to the endpoint clients use to obtain a token (relative to the API root).

def verify_password(plain_password:str, hashed_password:str) -> bool:
    return bcrypt.checkpw(plain_password.encode(), hashed_password.encode())

def get_password_hash(password:str) -> str:
    return bcrypt.hashpw(password.encode(), bcrypt.gensalt()).decode()

def create_access_token(data:dict, expires_delta:timedelta|None = None) -> str:
    to_encode = data.copy()
    expire = datetime.now(timezone.utc) + (expires_delta or timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES))
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, settings.SECRET_KEY, algorithm=settings.ALGORITHM)

def authenticate_user(db:Session, username:str, password:str) -> models.User | None:
    user = crud.get_user_by_username(db, username)
    if user is None or not verify_password(password, user.hashed_password):
        return None
    return user

def get_current_user(token:str = Depends(oauth2_scheme), db:Session = Depends(get_db)) -> models.User:
    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 = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenData(username=username)
    except JWTError as exc:
        raise credentials_exception from exc

    user = db.query(models.User).filter(models.User.username == token_data.username).first()
    if user is None:
        raise credentials_exception
    return user

def get_current_active_user(current_user:models.User = Depends(get_current_user)) -> models.User:
    if not current_user.is_active:
        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Inactive user")
    return current_user

def get_current_admin_user(current_user:models.User = Depends(get_current_active_user)) -> models.User:
    if not current_user.is_admin:
        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Admin privileges required")
    return current_user