api/auth.py

"""
Authentication utilities - JWT tokens, password hashing, OAuth helpers
"""
import os
import secrets
from datetime import datetime, timedelta
from typing import Optional, Dict, Any
from dotenv import load_dotenv

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

from api.database import get_db
from api.models import User

# Load environment variables
load_dotenv()

# Security configuration
SECRET_KEY = os.getenv("JWT_SECRET_KEY", secrets.token_urlsafe(32))
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 60 * 24 * 7  # 7 days

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

# HTTP Bearer token scheme
security = HTTPBearer(auto_error=False)


def hash_password(password: str) -> str:
    """Hash a password using bcrypt"""
    return pwd_context.hash(password)


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


def create_access_token(data: Dict[str, Any], expires_delta: Optional[timedelta] = None) -> str:
    """
    Create a JWT access token
    
    Args:
        data: Payload to encode (usually {"sub": user_id})
        expires_delta: Optional custom expiration time
    
    Returns:
        JWT token string
    """
    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 decode_access_token(token: str) -> Dict[str, Any]:
    """
    Decode and validate a JWT token
    
    Args:
        token: JWT token string
    
    Returns:
        Decoded payload
    
    Raises:
        HTTPException: If token is invalid or expired
    """
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        return payload
    except JWTError:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Could not validate credentials",
            headers={"WWW-Authenticate": "Bearer"},
        )


def get_current_user(
    credentials: HTTPAuthorizationCredentials = Depends(security),
    db: Session = Depends(get_db)
) -> Optional[User]:
    """
    Get current authenticated user from JWT token
    
    Usage:
        @app.get("/protected")
        def protected_route(user: User = Depends(get_current_user)):
            return {"message": f"Hello {user.email}"}
    
    Returns:
        User object if authenticated, None if optional auth
    """
    if not credentials:
        return None
    
    token = credentials.credentials
    payload = decode_access_token(token)
    
    user_id: int = payload.get("sub")
    if user_id is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid authentication credentials"
        )
    
    user = db.query(User).filter(User.id == user_id).first()
    if user is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="User not found"
        )
    
    # Update last login
    user.last_login = datetime.utcnow()
    db.commit()
    
    return user


def require_auth(user: User = Depends(get_current_user)) -> User:
    """
    Require authentication (raises 401 if not authenticated)
    
    Usage:
        @app.get("/protected")
        def protected_route(user: User = Depends(require_auth)):
            return {"message": f"Hello {user.email}"}
    """
    if user is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Authentication required",
            headers={"WWW-Authenticate": "Bearer"},
        )
    return user


def generate_state_token() -> str:
    """Generate a secure random state token for OAuth CSRF protection"""
    return secrets.token_urlsafe(32)