import secrets, re, typing
from nexios.config import get_config
from itsdangerous import URLSafeSerializer, BadSignature  # type:ignore
from nexios.middleware.base import BaseMiddleware
from nexios.http import Request, Response


class CSRFMiddleware(BaseMiddleware):
    """
    Middleware to protect against Cross-Site Request Forgery (CSRF) attacks for Nexios.
    """

    def __init__(self) -> None:
        app_config = get_config()
        self.use_csrf = app_config.csrf_enabled or False
        if self.use_csrf:
            assert app_config.secret_key != None, ""
        if not self.use_csrf:
            return
        self.serializer = URLSafeSerializer(
            app_config.secret_key, "csrftoken"
        )  # type:ignore
        self.required_urls: typing.List[str] = app_config.csrf_required_urls or []
        self.exempt_urls = app_config.csrf_exempt_urls
        self.sensitive_cookies = app_config.csrf_sensitive_cookies
        self.safe_methods = set(
            app_config.csrf_safe_methods
            or [
                "GET",
                "HEAD",
                "OPTIONS",
                "TRACE",
            ]
        )
        self.cookie_name = app_config.csrf_cookie_name or "csrftoken"
        self.cookie_path = app_config.csrf_cookie_path or "/"
        self.cookie_domain = app_config.csrf_cookie_domain
        self.cookie_secure = app_config.csrf_cookie_secure or False
        self.cookie_httponly = app_config.csrf_cookie_httponly or True
        self.cookie_samesite: typing.Literal["lax", "none", "strict"] = (
            app_config.csrf_cookie_samesite or "lax"
        )
        self.header_name = app_config.csrf_header_name or "X-CSRFToken"

    async def process_request(
        self,
        request: Request,
        response: Response,
        call_next: typing.Callable[..., typing.Awaitable[typing.Any]],
    ):
        """
        Process the incoming request to validate the CSRF token for unsafe HTTP methods.
        """

        if not self.use_csrf:
            await call_next()
            return
        csrf_cookie = request.cookies.get(self.cookie_name)
        if request.method.upper() in self.safe_methods:
            await call_next()
            return
        if self._url_is_required(request.url.path) or (
            self._url_is_exempt(request.url.path)
            and self._has_sensitive_cookies(request.cookies)
        ):
            submitted_csrf_token = request.headers.get(self.header_name)
            if not csrf_cookie:
                return response.text("CSRF token missing from cookies", status_code=403)

            if not submitted_csrf_token:
                return response.text("CSRF token missing from headers", status_code=403)

            if not self._csrf_tokens_match(csrf_cookie, submitted_csrf_token):
                return response.text("CSRF token incorrect", status_code=403)
        response.delete_cookie(self.cookie_name, self.cookie_path, self.cookie_domain)
        await call_next()

    async def process_response(self, request: Request, response: Response):
        """
        Inject the CSRF token into the response for client-side usage if not already set.
        """
        if not self.use_csrf:
            return
        csrf_token = self._generate_csrf_token()

        response.set_cookie(
            key=self.cookie_name,
            value=csrf_token,
            path=self.cookie_path,
            domain=self.cookie_domain,
            secure=self.cookie_secure,
            httponly=self.cookie_httponly,
            samesite=self.cookie_samesite,
        )

    def _has_sensitive_cookies(self, cookies: typing.Dict[str, typing.Any]) -> bool:
        """Check if the request contains sensitive cookies."""
        if not self.sensitive_cookies:
            return True
        for sensitive_cookie in self.sensitive_cookies:
            if sensitive_cookie in cookies:
                return True
        return False

    def _url_is_required(self, url: str) -> bool:
        """Check if the URL requires CSRF validation."""

        if not self.required_urls:
            return False

        if "*" in self.required_urls:
            return True
        for required_url in self.required_urls:
            match = re.match(required_url, url)
            if match and match.group() == url:
                return True
        return False

    def _url_is_exempt(self, url: str) -> bool:
        """Check if the URL is exempt from CSRF validation."""
        if not self.exempt_urls:
            return False
        for exempt_url in self.exempt_urls:
            match = re.match(exempt_url, url)
            if match and match.group() == url:
                return True
        return False

    def _generate_csrf_token(self) -> str:  # type:ignore
        """Generate a secure CSRF token."""
        return self.serializer.dumps(secrets.token_urlsafe(32))  # type:ignore

    def _csrf_tokens_match(self, token1: str, token2: str) -> bool:
        """Compare two CSRF tokens securely."""
        try:
            decoded1 = self.serializer.loads(token1)  # type:ignore
            decoded2 = self.serializer.loads(token2)  # type:ignore
            return secrets.compare_digest(decoded1, decoded2)  # type:ignore
        except BadSignature:
            return False
