CMT/backend/app/core/auth.py

"""
Authentication utilities for JWT-based session management with role-based expiration times.
"""
from datetime import datetime, timedelta, timezone
from typing import Optional, Union
import secrets
import hashlib
from jose import JWTError, jwt
from passlib.context import CryptContext
from fastapi import Depends, HTTPException, status, Request
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
from sqlmodel import Session, select
from app.core.config import settings
from app.core.db import get_session
from app.schemas.models import User
from app.schemas.schemas import TokenData, UserResponse
from app.schemas.base import UserRole

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

# Security scheme
security = HTTPBearer()


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


def get_password_hash(password: str) -> str:
    """Generate password hash."""
    return pwd_context.hash(password)


def authenticate_user(
        session: Session,
        username: str,
        password: str
        ) -> tuple[Optional[User], str]:
    """Authenticate user with username and password.
    
    Returns:
        tuple: (User object or None, error_message)
        error_message values:
        - "success" if authentication successful
        - "user_not_found" if username doesn't exist
        - "invalid_password" if password is incorrect
        - "account_pending_approval" if user exists but not approved
    """
    statement = select(User).where(User.username == username)
    user = session.exec(statement).first()
    if not user:
        return None, "user_not_found"
    if not verify_password(password, user.password_hash):
        return None, "invalid_password"
    # Check if user is approved
    if not user.is_approved:
        return None, "account_pending_approval"
    return user, "success"


def get_token_expiration_minutes(role: UserRole) -> int:
    """Get token expiration time based on user role."""
    role_expiration_map = {
        UserRole.ADMIN: settings.admin_token_expire_minutes,
        UserRole.WRITE: settings.write_token_expire_minutes,
        UserRole.READ_ONLY: settings.read_only_token_expire_minutes,
    }
    return role_expiration_map.get(role, settings.read_only_token_expire_minutes)


def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    """Create JWT access token."""
    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 verify_token(credentials: HTTPAuthorizationCredentials = Depends(security)) -> TokenData:
    """Verify JWT token and extract token data."""
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    
    try:
        token = credentials.credentials
        payload = jwt.decode(token, settings.secret_key, algorithms=[settings.algorithm])
        username: Optional[str] = payload.get("sub")
        user_id: Optional[int] = payload.get("user_id")
        role: Optional[str] = payload.get("role")
        
        if username is None or user_id is None or role is None:
            raise credentials_exception
            
        token_data = TokenData(
            username=username,
            user_id=user_id,
            role=UserRole(role)
        )
    except JWTError:
        raise credentials_exception
    
    return token_data


def get_current_user(
    token_data: TokenData = Depends(verify_token),
    session: Session = Depends(get_session)
) -> User:
    """Get current user from token."""
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    
    user = session.get(User, token_data.user_id)
    if user is None:
        raise credentials_exception
    return user


def get_current_active_user(
        current_user: UserResponse = Depends(get_current_user)
        ) -> UserResponse:
    """Get current active user (extend this if you add user activation status)."""
    return current_user


def require_role(required_roles: list[UserRole]):
    """Dependency factory for role-based access control."""
    def role_checker(current_user: User = Depends(get_current_active_user)) -> User:
        if current_user.role not in required_roles:
            raise HTTPException(
                status_code=status.HTTP_403_FORBIDDEN,
                detail="Operation not permitted for your role"
            )
        return current_user
    return role_checker


# Common role dependencies
require_admin = require_role([UserRole.ADMIN])
require_write_access = require_role([UserRole.ADMIN, UserRole.WRITE])
require_any_access = require_role([UserRole.ADMIN, UserRole.WRITE, UserRole.READ_ONLY])


def send_password_reset_email(username: str, email: str) -> bool:
    """Send password reset instructions via email (mock implementation)."""
    # In a real application, you would:
    # 1. Verify the email belongs to the username
    # 2. Send an email with instructions to reset password
    # 3. The email would contain a link to your frontend with instructions
    
    print(f"Mock: Sending password reset email to {email} for user {username}")
    print("Instructions: Please contact your system administrator to reset your password.")
    
    # Return True to indicate email was "sent"
    return True