import hashlib
import os
from datetime import datetime, timedelta
from typing import Optional
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from sqlmodel import Session, select
from app.database import get_session
from app.models import User

# Configuration
SECRET_KEY = "super-secret-key-change-this-in-production"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="auth/token")

def get_password_hash(password: str) -> str:
    """Hash a password using SHA-256 with a random salt."""
    salt = os.urandom(32)
    key = hashlib.pbkdf2_hmac('sha256', password.encode('utf-8'), salt, 100000)
    return salt.hex() + ':' + key.hex()

def verify_password(plain_password: str, hashed_password: str) -> bool:
    """Verify a password against its stored hash."""
    try:
        salt_hex, key_hex = hashed_password.split(':', 1)
        salt = bytes.fromhex(salt_hex)
        key = bytes.fromhex(key_hex)
        new_key = hashlib.pbkdf2_hmac('sha256', plain_password.encode('utf-8'), salt, 100000)
        return new_key == key
    except (ValueError, AttributeError):
        return False

def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

async def get_current_user(token: str = Depends(oauth2_scheme), session: Session = Depends(get_session)):
    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
    except JWTError:
        raise credentials_exception
        
    user = session.exec(select(User).where(User.username == username)).first()
    if user is None:
        raise credentials_exception
    return user