"""Cryptographic utilities for OAuth 2.0 (RFC 8705).

This module implements mutual TLS authentication and certificate-bound
access tokens as defined in RFC 8705.

RFC 8705: OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens
https://datatracker.ietf.org/doc/html/rfc8705

Key Features:
- Certificate-based client authentication (mTLS)
- Certificate-bound access tokens for enhanced security
- Certificate thumbprint generation and validation
- X.509 certificate utilities

Security Benefits:
- Prevents token theft and replay attacks
- Eliminates client secret management issues
- Enables zero-trust architecture patterns
- Strong cryptographic authentication
"""

from pydantic import BaseModel


class CertificateBoundToken(BaseModel):
    """Certificate-bound access token metadata for RFC 8705.

    Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-3
    """

    x5t_s256: str  # SHA256 thumbprint of the certificate
    certificate_dn: str | None = None  # Certificate Distinguished Name


class MutualTLSClientAuth:
    """Mutual TLS client authentication utilities for RFC 8705.

    Implements certificate-based client authentication and certificate-bound
    access tokens as specified in RFC 8705.

    Reference: https://datatracker.ietf.org/doc/html/rfc8705

    Example:
        auth = MutualTLSClientAuth()

        # Generate certificate thumbprint for token binding
        thumbprint = auth.generate_cert_thumbprint(client_cert_pem)

        # Validate certificate-bound token
        is_valid = auth.validate_cert_bound_token(
            access_token=jwt_token,
            client_certificate=cert_pem
        )
    """

    @staticmethod
    def generate_cert_thumbprint(certificate_pem: str) -> str:
        """Generate SHA256 thumbprint of X.509 certificate.

        Creates the x5t#S256 thumbprint used for certificate-bound tokens
        as defined in RFC 8705 Section 3.

        Args:
            certificate_pem: X.509 certificate in PEM format

        Returns:
            Base64url-encoded SHA256 thumbprint

        Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-3
        """
        # Implementation placeholder
        raise NotImplementedError(
            "Certificate thumbprint generation not yet implemented"
        )

    @staticmethod
    def extract_certificate_info(certificate_pem: str) -> dict:
        """Extract relevant information from X.509 certificate.

        Parses certificate to extract subject DN, issuer, validity dates,
        and other metadata useful for mTLS authentication.

        Args:
            certificate_pem: X.509 certificate in PEM format

        Returns:
            Dictionary containing certificate metadata

        Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-2
        """
        # Implementation placeholder
        raise NotImplementedError("Certificate parsing not yet implemented")

    def validate_cert_bound_token(
        self, access_token: str, client_certificate: str
    ) -> bool:
        """Validate certificate-bound access token.

        Verifies that the access token is bound to the provided client
        certificate by comparing certificate thumbprints.

        Args:
            access_token: JWT access token (should contain cnf claim)
            client_certificate: Client certificate in PEM format

        Returns:
            True if token is bound to certificate, False otherwise

        Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-3
        """
        # Implementation placeholder
        raise NotImplementedError(
            "Certificate-bound token validation not yet implemented"
        )

    def create_certificate_bound_token(
        self, base_token: dict, certificate_pem: str
    ) -> dict:
        """Create certificate-bound access token.

        Adds the cnf (confirmation) claim to an access token to bind it
        to a specific client certificate.

        Args:
            base_token: Base JWT payload dictionary
            certificate_pem: Client certificate in PEM format

        Returns:
            Token payload with cnf claim added

        Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-3.1
        """
        # Implementation placeholder
        raise NotImplementedError(
            "Certificate-bound token creation not yet implemented"
        )

    @staticmethod
    def validate_certificate_chain(
        certificate_pem: str, ca_bundle: str | None = None
    ) -> bool:
        """Validate X.509 certificate chain.

        Validates certificate chain up to trusted root CA and checks
        certificate validity dates and revocation status.

        Args:
            certificate_pem: Client certificate in PEM format
            ca_bundle: Optional CA bundle for validation

        Returns:
            True if certificate chain is valid, False otherwise

        Reference: https://datatracker.ietf.org/doc/html/rfc8705#section-2
        """
        # Implementation placeholder
        raise NotImplementedError("Certificate chain validation not yet implemented")
