import os
from datetime import datetime, timedelta, timezone
from itsdangerous import URLSafeTimedSerializer, BadSignature, SignatureExpired
from fastapi import Request, Response
from db import get_user_by_id

SECRET_KEY = os.environ.get("SECRET_KEY", "dev-secret-key-change-in-production")
COOKIE_NAME = "session"
DEFAULT_SESSION_MAX_AGE_DAYS = 7
SECONDS_PER_DAY = 24 * 3600


def session_max_age_seconds() -> int:
    raw_days = os.environ.get("SESSION_MAX_AGE_DAYS", "").strip()
    if not raw_days:
        return DEFAULT_SESSION_MAX_AGE_DAYS * SECONDS_PER_DAY
    try:
        days = int(raw_days)
    except ValueError:
        return DEFAULT_SESSION_MAX_AGE_DAYS * SECONDS_PER_DAY
    if days < 1:
        return DEFAULT_SESSION_MAX_AGE_DAYS * SECONDS_PER_DAY
    return days * SECONDS_PER_DAY


MAX_AGE = session_max_age_seconds()

_serializer = URLSafeTimedSerializer(SECRET_KEY)


def create_session_token(user_id: int) -> str:
    return _serializer.dumps({"user_id": user_id})


def verify_session_token(token: str) -> int | None:
    try:
        data = _serializer.loads(token, max_age=MAX_AGE)
        return data.get("user_id")
    except (BadSignature, SignatureExpired):
        return None


def set_session_cookie(response: Response, user_id: int):
    token = create_session_token(user_id)
    response.set_cookie(
        COOKIE_NAME,
        token,
        max_age=MAX_AGE,
        httponly=True,
        samesite="lax",
        secure=os.environ.get("SECURE_COOKIES", "false").lower() == "true",
    )


def clear_session_cookie(response: Response):
    response.delete_cookie(COOKIE_NAME)


def get_current_user(request: Request) -> dict | None:
    token = request.cookies.get(COOKIE_NAME)
    return get_current_user_from_token(token)


def get_current_user_from_token(token: str | None) -> dict | None:
    if not token:
        return None
    user_id = verify_session_token(token)
    if not user_id:
        return None
    return get_user_by_id(user_id)