"""
QUIC Security implementation for py-libp2p Module 5.
Implements libp2p TLS specification for QUIC transport with peer identity integration.
Based on go-libp2p and js-libp2p security patterns.
"""

from dataclasses import dataclass
import logging
import time
from typing import Optional, Tuple

from cryptography import x509
from cryptography.hazmat.primitives import hashes, serialization
from cryptography.hazmat.primitives.asymmetric import ec, rsa
from cryptography.x509.oid import NameOID

from libp2p.crypto.ed25519 import Ed25519PublicKey
from libp2p.crypto.keys import PrivateKey, PublicKey
from libp2p.crypto.secp256k1 import Secp256k1PublicKey
from libp2p.peer.id import ID

from .exceptions import (
    QUICCertificateError,
    QUICPeerVerificationError,
)

logger = logging.getLogger(__name__)

# libp2p TLS Extension OID - Official libp2p specification
LIBP2P_TLS_EXTENSION_OID = x509.ObjectIdentifier("1.3.6.1.4.1.53594.1.1")

# Certificate validity period
CERTIFICATE_VALIDITY_DAYS = 365
CERTIFICATE_NOT_BEFORE_BUFFER = 3600  # 1 hour before now


@dataclass
class TLSConfig:
    """TLS configuration for QUIC transport with libp2p extensions."""

    certificate: x509.Certificate
    private_key: ec.EllipticCurvePrivateKey | rsa.RSAPrivateKey
    peer_id: ID

    def get_certificate_der(self) -> bytes:
        """Get certificate in DER format for aioquic."""
        return self.certificate.public_bytes(serialization.Encoding.DER)

    def get_private_key_der(self) -> bytes:
        """Get private key in DER format for aioquic."""
        return self.private_key.private_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PrivateFormat.PKCS8,
            encryption_algorithm=serialization.NoEncryption(),
        )


class LibP2PExtensionHandler:
    """
    Handles libp2p-specific TLS extensions for peer identity verification.

    Based on libp2p TLS specification:
    https://github.com/libp2p/specs/blob/master/tls/tls.md
    """

    @staticmethod
    def create_signed_key_extension(
        libp2p_private_key: PrivateKey, cert_public_key: bytes
    ) -> bytes:
        """
        Create the libp2p Public Key Extension with signed key proof.

        The extension contains:
        1. The libp2p public key
        2. A signature proving ownership of the private key

        Args:
            libp2p_private_key: The libp2p identity private key
            cert_public_key: The certificate's public key bytes

        Returns:
            ASN.1 encoded extension value

        """
        try:
            # Get the libp2p public key
            libp2p_public_key = libp2p_private_key.get_public_key()

            # Create the signature payload: "libp2p-tls-handshake:" + cert_public_key
            signature_payload = b"libp2p-tls-handshake:" + cert_public_key

            # Sign the payload with the libp2p private key
            signature = libp2p_private_key.sign(signature_payload)

            # Create the SignedKey structure (simplified ASN.1 encoding)
            # In a full implementation, this would use proper ASN.1 encoding
            public_key_bytes = libp2p_public_key.serialize()

            # Simple encoding: [public_key_length][public_key][signature_length][signature]
            extension_data = (
                len(public_key_bytes).to_bytes(4, byteorder="big")
                + public_key_bytes
                + len(signature).to_bytes(4, byteorder="big")
                + signature
            )

            return extension_data

        except Exception as e:
            raise QUICCertificateError(
                f"Failed to create signed key extension: {e}"
            ) from e

    @staticmethod
    def parse_signed_key_extension(extension_data: bytes) -> Tuple[PublicKey, bytes]:
        """
        Parse the libp2p Public Key Extension to extract public key and signature.

        Args:
            extension_data: The extension data bytes

        Returns:
            Tuple of (libp2p_public_key, signature)

        Raises:
            QUICCertificateError: If extension parsing fails

        """
        try:
            offset = 0

            # Parse public key length and data
            if len(extension_data) < 4:
                raise QUICCertificateError("Extension too short for public key length")

            public_key_length = int.from_bytes(
                extension_data[offset : offset + 4], byteorder="big"
            )
            offset += 4

            if len(extension_data) < offset + public_key_length:
                raise QUICCertificateError("Extension too short for public key data")

            public_key_bytes = extension_data[offset : offset + public_key_length]
            offset += public_key_length

            # Parse signature length and data
            if len(extension_data) < offset + 4:
                raise QUICCertificateError("Extension too short for signature length")

            signature_length = int.from_bytes(
                extension_data[offset : offset + 4], byteorder="big"
            )
            offset += 4

            if len(extension_data) < offset + signature_length:
                raise QUICCertificateError("Extension too short for signature data")

            signature = extension_data[offset : offset + signature_length]

            # Deserialize the public key
            # This is a simplified approach - full implementation would handle all key types
            public_key = LibP2PKeyConverter.deserialize_public_key(public_key_bytes)

            return public_key, signature

        except Exception as e:
            raise QUICCertificateError(
                f"Failed to parse signed key extension: {e}"
            ) from e


class LibP2PKeyConverter:
    """
    Converts between libp2p key formats and cryptography library formats.
    Handles different key types: Ed25519, Secp256k1, RSA, ECDSA.
    """

    @staticmethod
    def libp2p_to_tls_private_key(
        libp2p_key: PrivateKey,
    ) -> ec.EllipticCurvePrivateKey | rsa.RSAPrivateKey:
        """
        Convert libp2p private key to TLS-compatible private key.

        For certificate generation, we create a separate ephemeral key
        rather than using the libp2p identity key directly.
        """
        # For QUIC, we prefer ECDSA keys for smaller certificates
        # Generate ephemeral P-256 key for certificate signing
        private_key = ec.generate_private_key(ec.SECP256R1())
        return private_key

    @staticmethod
    def serialize_public_key(public_key: PublicKey) -> bytes:
        """Serialize libp2p public key to bytes."""
        return public_key.serialize()

    @staticmethod
    def deserialize_public_key(key_bytes: bytes) -> PublicKey:
        """
        Deserialize libp2p public key from bytes.

        This is a simplified implementation - full version would handle
        all libp2p key types and proper deserialization.
        """
        # For now, assume Ed25519 keys (most common in libp2p)
        # Full implementation would detect key type from bytes
        try:
            return Ed25519PublicKey.deserialize(key_bytes)
        except Exception:
            # Fallback to other key types
            try:
                return Secp256k1PublicKey.deserialize(key_bytes)
            except Exception:
                raise QUICCertificateError("Unsupported key type in extension")


class CertificateGenerator:
    """
    Generates X.509 certificates with libp2p peer identity extensions.
    Follows libp2p TLS specification for QUIC transport.
    """

    def __init__(self):
        self.extension_handler = LibP2PExtensionHandler()
        self.key_converter = LibP2PKeyConverter()

    def generate_certificate(
        self,
        libp2p_private_key: PrivateKey,
        peer_id: ID,
        validity_days: int = CERTIFICATE_VALIDITY_DAYS,
    ) -> TLSConfig:
        """
        Generate a TLS certificate with embedded libp2p peer identity.

        Args:
            libp2p_private_key: The libp2p identity private key
            peer_id: The libp2p peer ID
            validity_days: Certificate validity period in days

        Returns:
            TLSConfig with certificate and private key

        Raises:
            QUICCertificateError: If certificate generation fails

        """
        try:
            # Generate ephemeral private key for certificate
            cert_private_key = self.key_converter.libp2p_to_tls_private_key(
                libp2p_private_key
            )
            cert_public_key = cert_private_key.public_key()

            # Get certificate public key bytes for extension
            cert_public_key_bytes = cert_public_key.public_bytes(
                encoding=serialization.Encoding.DER,
                format=serialization.PublicFormat.SubjectPublicKeyInfo,
            )

            # Create libp2p extension with signed key proof
            extension_data = self.extension_handler.create_signed_key_extension(
                libp2p_private_key, cert_public_key_bytes
            )

            # Set validity period
            now = time.time()
            not_before = time.gmtime(now - CERTIFICATE_NOT_BEFORE_BUFFER)
            not_after = time.gmtime(now + (validity_days * 24 * 3600))

            # Build certificate
            certificate = (
                x509.CertificateBuilder()
                .subject_name(
                    x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, str(peer_id))])
                )
                .issuer_name(
                    x509.Name([x509.NameAttribute(NameOID.COMMON_NAME, str(peer_id))])
                )
                .public_key(cert_public_key)
                .serial_number(int(now))  # Use timestamp as serial number
                .not_valid_before(time.struct_time(not_before))
                .not_valid_after(time.struct_time(not_after))
                .add_extension(
                    x509.UnrecognizedExtension(
                        oid=LIBP2P_TLS_EXTENSION_OID, value=extension_data
                    ),
                    critical=True,  # This extension is critical for libp2p
                )
                .sign(cert_private_key, hashes.SHA256())
            )

            logger.info(f"Generated libp2p TLS certificate for peer {peer_id}")

            return TLSConfig(
                certificate=certificate, private_key=cert_private_key, peer_id=peer_id
            )

        except Exception as e:
            raise QUICCertificateError(f"Failed to generate certificate: {e}") from e


class PeerAuthenticator:
    """
    Authenticates remote peers using libp2p TLS certificates.
    Validates both TLS certificate integrity and libp2p peer identity.
    """

    def __init__(self):
        self.extension_handler = LibP2PExtensionHandler()

    def verify_peer_certificate(
        self, certificate: x509.Certificate, expected_peer_id: Optional[ID] = None
    ) -> ID:
        """
        Verify a peer's TLS certificate and extract/validate peer identity.

        Args:
            certificate: The peer's TLS certificate
            expected_peer_id: Expected peer ID (for outbound connections)

        Returns:
            The verified peer ID

        Raises:
            QUICPeerVerificationError: If verification fails

        """
        try:
            # Extract libp2p extension
            libp2p_extension = None
            for extension in certificate.extensions:
                if extension.oid == LIBP2P_TLS_EXTENSION_OID:
                    libp2p_extension = extension
                    break

            if not libp2p_extension:
                raise QUICPeerVerificationError("Certificate missing libp2p extension")

            # Parse the extension to get public key and signature
            public_key, signature = self.extension_handler.parse_signed_key_extension(
                libp2p_extension.value
            )

            # Get certificate public key for signature verification
            cert_public_key_bytes = certificate.public_key().public_bytes(
                encoding=serialization.Encoding.DER,
                format=serialization.PublicFormat.SubjectPublicKeyInfo,
            )

            # Verify the signature proves ownership of the libp2p private key
            signature_payload = b"libp2p-tls-handshake:" + cert_public_key_bytes

            try:
                public_key.verify(signature, signature_payload)
            except Exception as e:
                raise QUICPeerVerificationError(
                    f"Invalid signature in libp2p extension: {e}"
                )

            # Derive peer ID from public key
            derived_peer_id = ID.from_pubkey(public_key)

            # Verify against expected peer ID if provided
            if expected_peer_id and derived_peer_id != expected_peer_id:
                raise QUICPeerVerificationError(
                    f"Peer ID mismatch: expected {expected_peer_id}, got {derived_peer_id}"
                )

            logger.info(f"Successfully verified peer certificate for {derived_peer_id}")
            return derived_peer_id

        except QUICPeerVerificationError:
            raise
        except Exception as e:
            raise QUICPeerVerificationError(
                f"Certificate verification failed: {e}"
            ) from e


class QUICTLSConfigManager:
    """
    Manages TLS configuration for QUIC transport with libp2p security.
    Integrates with aioquic's TLS configuration system.
    """

    def __init__(self, libp2p_private_key: PrivateKey, peer_id: ID):
        self.libp2p_private_key = libp2p_private_key
        self.peer_id = peer_id
        self.certificate_generator = CertificateGenerator()
        self.peer_authenticator = PeerAuthenticator()

        # Generate certificate for this peer
        self.tls_config = self.certificate_generator.generate_certificate(
            libp2p_private_key, peer_id
        )

    def create_server_config(self) -> dict:
        """
        Create aioquic server configuration with libp2p TLS settings.

        Returns:
            Configuration dictionary for aioquic QuicConfiguration

        """
        return {
            "certificate": self.tls_config.get_certificate_der(),
            "private_key": self.tls_config.get_private_key_der(),
            "alpn_protocols": ["libp2p"],  # Required ALPN protocol
            "verify_mode": True,  # Require client certificates
        }

    def create_client_config(self) -> dict:
        """
        Create aioquic client configuration with libp2p TLS settings.

        Returns:
            Configuration dictionary for aioquic QuicConfiguration

        """
        return {
            "certificate": self.tls_config.get_certificate_der(),
            "private_key": self.tls_config.get_private_key_der(),
            "alpn_protocols": ["libp2p"],  # Required ALPN protocol
            "verify_mode": True,  # Verify server certificate
        }

    def verify_peer_identity(
        self, peer_certificate: x509.Certificate, expected_peer_id: Optional[ID] = None
    ) -> ID:
        """
        Verify remote peer's identity from their TLS certificate.

        Args:
            peer_certificate: Remote peer's TLS certificate
            expected_peer_id: Expected peer ID (for outbound connections)

        Returns:
            Verified peer ID

        """
        return self.peer_authenticator.verify_peer_certificate(
            peer_certificate, expected_peer_id
        )

    def get_local_peer_id(self) -> ID:
        """Get the local peer ID."""
        return self.peer_id


# Factory function for creating QUIC security transport
def create_quic_security_transport(
    libp2p_private_key: PrivateKey, peer_id: ID
) -> QUICTLSConfigManager:
    """
    Factory function to create QUIC security transport.

    Args:
        libp2p_private_key: The libp2p identity private key
        peer_id: The libp2p peer ID

    Returns:
        Configured QUIC TLS manager

    """
    return QUICTLSConfigManager(libp2p_private_key, peer_id)


# Legacy compatibility functions for existing code
def generate_libp2p_tls_config(private_key: PrivateKey, peer_id: ID) -> TLSConfig:
    """
    Legacy function for compatibility with existing transport code.

    Args:
        private_key: libp2p private key
        peer_id: libp2p peer ID

    Returns:
        TLS configuration

    """
    generator = CertificateGenerator()
    return generator.generate_certificate(private_key, peer_id)


def cleanup_tls_config(config: TLSConfig) -> None:
    """
    Clean up TLS configuration.

    For the new implementation, this is mostly a no-op since we don't use
    temporary files, but kept for compatibility.
    """
    # New implementation doesn't use temporary files
    logger.debug("TLS config cleanup completed")