import os
import httpx
import logging
from core.models import IngestedDocument, DocumentClassificationResult, DocumentType, ProcessingPolicy, PdfType
from extraction.magic_numbers import MagicNumberValidator
from extraction.pdf_inspector import PDFInspector

logger = logging.getLogger("DCE")

class DocumentClassificationEngine:
    """
    Document Classification Engine (DCE).
    """
    def __init__(self):
        self.pdf_inspector = PDFInspector()

    def classify(self, document: IngestedDocument) -> DocumentClassificationResult:
        logger.info(f"Classifying document: {document.name} (ID: {document.item_id})")
        
        ext = os.path.splitext(document.name)[1].lower()
        
        doc_type = DocumentType.UNKNOWN
        policy = ProcessingPolicy.UNSUPPORTED
        reason = "Initial state"
        
        # 1. Magic Number Validation
        if document.download_url:
            header_bytes = MagicNumberValidator.fetch_header_bytes(document.download_url)
            is_valid, detected_type, sig_desc = MagicNumberValidator.validate_from_bytes(header_bytes)
            if is_valid:
                logger.info(f"Magic Number match: {sig_desc}")
            else:
                logger.warning(f"Could not verify magic number for {document.name}. Trusting extension fallback.")

        # 2. Routing Rules
        if ext == ".pdf":
            pdf_type = PdfType.SCAN_PDF # Simulated default
            if document.download_url:
                logger.info("Downloading PDF into memory for PyMuPDF inspection...")
                try:
                    with httpx.Client() as client:
                        resp = client.get(document.download_url)
                        resp.raise_for_status()
                        pdf_bytes = resp.content
                    pdf_type = self.pdf_inspector.inspect_pdf_from_bytes(pdf_bytes)
                except Exception as e:
                    logger.error(f"Failed to download/inspect PDF: {e}")
                    pdf_type = PdfType.SCAN_PDF
            else:
                logger.warning("No download_url available for PDF. Defaulting to SCAN_PDF.")
            
            if pdf_type == PdfType.TEXT_PDF:
                doc_type = DocumentType.TEXTUAL_DOCUMENT
                policy = ProcessingPolicy.SKIP_OCR
                reason = "PDF has text layer (TEXT_PDF)"
            elif pdf_type == PdfType.DRAWING_PDF:
                doc_type = DocumentType.DRAWING
                policy = ProcessingPolicy.METADATA_ONLY
                reason = "PDF has large vector dimensions (DRAWING_PDF)"
            elif pdf_type == PdfType.AMBIGUOUS_PDF:
                doc_type = DocumentType.UNKNOWN
                policy = ProcessingPolicy.REQUIRES_REVIEW
                reason = "Kích thước PDF lớn bất thường (khổ A3/A2 hoặc DPI cao), cần con người xác nhận là bản Scan hay Bản vẽ"
            else:
                doc_type = DocumentType.TEXTUAL_DOCUMENT
                policy = ProcessingPolicy.REQUIRES_OCR
                reason = "PDF has no text layer (SCAN_PDF)"
                
        elif ext in [".docx", ".doc", ".txt", ".md"]:
            doc_type = DocumentType.TEXTUAL_DOCUMENT
            policy = ProcessingPolicy.SKIP_OCR
            reason = "Standard textual document format"
            
        elif ext in [".xlsx", ".xls", ".csv"]:
            doc_type = DocumentType.SPREADSHEET
            policy = ProcessingPolicy.SKIP_OCR
            reason = "Spreadsheet document format"
            
        elif ext in [".dwg", ".dxf", ".cad"]:
            doc_type = DocumentType.DRAWING
            policy = ProcessingPolicy.METADATA_ONLY
            reason = "Native CAD drawing format"
            
        else:
            doc_type = DocumentType.BINARY
            policy = ProcessingPolicy.UNSUPPORTED
            reason = f"Unsupported or binary extension: {ext}"

        result = DocumentClassificationResult(
            item_id=document.item_id,
            doc_type=doc_type,
            processing_policy=policy,
            file_extension=ext,
            is_supported=policy != ProcessingPolicy.UNSUPPORTED,
            reason=reason
        )
        
        logger.info(f"Result -> Type: {doc_type.value}, Policy: {policy.value}, Reason: {reason}")
        return result