from typing import Dict, Any, Tuple
import httpx
import logging
from core.models import IngestedDocument, DocumentClassificationResult, DocumentType, ProcessingPolicy

logger = logging.getLogger("DCE")

class MagicNumberValidator:
    """Validates file types using magic numbers (file signatures)."""
    
    SIGNATURES = {
        b"%PDF-": (DocumentType.TEXTUAL_DOCUMENT, "PDF Document"),
        b"PK\x03\x04": (DocumentType.UNKNOWN, "ZIP Archive / Office Open XML"), # Needs further check
        b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1": (DocumentType.UNKNOWN, "Legacy Office Document"),
        # Add CAD magic numbers here if needed (e.g., AutoCAD DWG: b"AC10")
        b"AC10": (DocumentType.DRAWING, "AutoCAD Drawing (DWG)")
    }

    @classmethod
    def validate_from_bytes(cls, header_bytes: bytes) -> Tuple[bool, DocumentType, str]:
        """Checks if the bytes match any known signature."""
        for sig, (doc_type, desc) in cls.SIGNATURES.items():
            if header_bytes.startswith(sig):
                return True, doc_type, desc
        return False, DocumentType.UNKNOWN, "Unknown Signature"

    @classmethod
    def fetch_header_bytes(cls, download_url: str, num_bytes: int = 256) -> bytes:
        """Fetches only the first N bytes of a file using HTTP Range request."""
        try:
            # Idea: HTTP Range request prevents downloading huge files just to check headers
            headers = {"Range": f"bytes=0-{num_bytes - 1}"}
            with httpx.Client() as client:
                response = client.get(download_url, headers=headers)
                response.raise_for_status()
                return response.content
        except Exception as e:
            logger.error(f"Failed to fetch header bytes: {e}")
            return b""