# backend/app/core/auth.py
from datetime import datetime, timedelta, timezone
from typing import Optional
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
import jwt
from jwt.exceptions import PyJWTError

from .config import SECRET_KEY, ALGORITHM

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="auth/token")
oauth2_scheme_optional = OAuth2PasswordBearer(tokenUrl="auth/token", auto_error=False)


def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    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, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt


async def get_authenticated_user(token: str = Depends(oauth2_scheme)):
    """Allows both Admins and Refs"""
    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])
        role = payload.get("role")
        if role not in ["admin", "ref"]:
            raise credentials_exception
        return payload
    except PyJWTError:
        raise credentials_exception


async def get_admin_user(token: str = Depends(oauth2_scheme)):
    """Strictly allows ONLY Admins"""
    user = await get_authenticated_user(token)
    if user.get("role") != "admin":
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN, detail="Admin privileges required"
        )
    return user


async def get_optional_user(
    token: Optional[str] = Depends(oauth2_scheme_optional),
) -> Optional[dict]:
    """Returns user payload if valid token exists, else None"""
    if not token:
        return None
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        if payload.get("role") in ["admin", "ref"]:
            return payload
    except Exception:
        pass
    return None