"""
Public Key Authentication Implementation

Implements SSH public key authentication method according to RFC 4252.
"""

from typing import Any
from ..exceptions import AuthenticationException


class PublicKeyAuth:
    """
    SSH public key authentication implementation.
    
    Handles public key-based authentication with support for
    Ed25519, ECDSA, and RSA keys.
    """
    
    def __init__(self, transport: Any) -> None:
        """
        Initialize public key authentication.
        
        Args:
            transport: SSH transport instance
        """
        self._transport = transport
    
    def authenticate(self, username: str, key: Any) -> bool:
        """
        Perform public key authentication.
        
        Args:
            username: Username for authentication
            key: Private key for authentication
            
        Returns:
            True if authentication successful
            
        Raises:
            AuthenticationException: If authentication fails
        """
        # Implementation will be added in later tasks
        raise NotImplementedError("PublicKeyAuth.authenticate will be implemented in task 4.2")