from datetime import datetime, timedelta
from typing import Optional

from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from jose import jwt, JWTError
from passlib.context import CryptContext
from sqlalchemy.orm import Session

from .db import SessionLocal
from . import models
from .config import settings

SECRET_KEY = settings.secret_key
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = settings.access_token_expire_minuted

pwd_context = CryptContext(schemes=["bcrypt_sha256"], deprecated="auto")
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/token")

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

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 authenticate_user(db: Session, username: str, password: str) -> Optional[models.User]:
    user = db.query(models.User).filter(models.User.username == username).first()
    if not user or not verify_password(password, user.password_hash):
        return None
    return user

def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    to_encode = data.copy()
    expire = datetime.utcnow() + (expires_delta or timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES))
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)

async 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, SECRET_KEY, algorithms=[ALGORITHM])
        username: str | None = payload.get("preferred_username") or payload.get("sub")
        if username is None:
            raise credentials_exception
    except JWTError:
        raise credentials_exception
    user = db.query(models.User).filter(models.User.username == username).first()
    if user is None:
        raise credentials_exception
    return user