"""
Authentication Service
Password hashing and JWT token generation
"""
from datetime import datetime, timedelta
from typing import Optional
from passlib.context import CryptContext
from jose import JWTError, jwt
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from sqlalchemy.orm import Session

from app.config import SECRET_KEY, ALGORITHM, ACCESS_TOKEN_EXPIRE_MINUTES
from app.database import get_db
from app.models import User
from app.schemas import TokenData

# Password hashing (using argon2 instead of bcrypt for Python 3.13 compatibility)
pwd_context = CryptContext(schemes=["argon2"], deprecated="auto")

# OAuth2 scheme
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login")


def verify_password(plain_password: str, hashed_password: str) -> bool:
    """Verify a password against a hash"""
    return pwd_context.verify(plain_password, hashed_password)


def get_password_hash(password: str) -> str:
    """Hash a password"""
    # Bcrypt has a 72 byte limit, truncate if necessary
    if len(password.encode('utf-8')) > 72:
        password = password[:72]
    return pwd_context.hash(password)


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


def authenticate_user(db: Session, username: str, password: str):
    """Authenticate user with username and password"""
    user = db.query(User).filter(User.username == username).first()
    if not user:
        return False
    if not verify_password(password, user.hashed_password):
        return False
    return user


async def get_current_user(
    token: str = Depends(oauth2_scheme),
    db: Session = Depends(get_db)
) -> User:
    """Get current authenticated user from JWT token"""
    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 = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenData(username=username)
    except JWTError:
        raise credentials_exception
    
    user = db.query(User).filter(User.username == token_data.username).first()
    if user is None:
        raise credentials_exception
    
    return user