agents/verification_agent.py

"""
Verification Agent
Verifies proof authenticity by recomputing and comparing hashes.
"""

from typing import Dict, Any
import hashlib
from datetime import datetime, timezone

from core.agent_base import Agent
from core.errors import VerificationError
from models.proof import VerificationResult, Proof
from agents.storage_agent import StorageAgent


class VerificationAgent(Agent):
    """
    Verifies proof by fetching from storage and recomputing hash.
    """
    
    def __init__(self, storage_agent: StorageAgent):
        super().__init__()
        self.storage_agent = storage_agent
    
    def execute(self, input_data: Dict[str, Any]) -> Dict[str, Any]:
        """
        Verify proof authenticity.
        
        Expected input_data:
            {
                "proof_id": str,
                "content": bytes  # Original content to verify
            }
        
        Returns:
            {
                "verification_result": VerificationResult
            }
        """
        proof_id = input_data.get("proof_id")
        content = input_data.get("content")
        
        if not proof_id:
            raise VerificationError("Missing 'proof_id'")
        
        if not content:
            raise VerificationError("Missing 'content' to verify")
        
        # Fetch original proof
        proof = self.storage_agent.get_proof(proof_id)
        
        if not proof:
            raise VerificationError(f"Proof not found: {proof_id}")
        
        # Recompute hash
        computed_hash = self._compute_hash(content, proof.hash_algorithm)
        
        # Compare hashes
        is_valid = computed_hash == proof.content_hash
        
        result = VerificationResult(
            proof_id=proof_id,
            is_valid=is_valid,
            original_hash=proof.content_hash,
            computed_hash=computed_hash,
            timestamp=datetime.now(timezone.utc).isoformat(),
            message="Hash match: proof is valid" if is_valid else "Hash mismatch: proof is invalid"
        )
        
        return {
            "verification_result": result
        }
    
    def _compute_hash(self, content: bytes, algorithm: str) -> str:
        """
        Compute hash using specified algorithm.
        
        Args:
            content: Content bytes to hash
            algorithm: Hash algorithm name
            
        Returns:
            Hexadecimal hash string
        """
        try:
            hasher = hashlib.new(algorithm)
            hasher.update(content)
            return hasher.hexdigest()
        except Exception as e:
            raise VerificationError(f"Hash computation failed: {str(e)}") from e