office_translator/utils/file_handler.py

"""
Utility functions for file handling and validation
"""

import os
import uuid
import hashlib
from pathlib import Path
from typing import Optional
from fastapi import UploadFile, HTTPException
from config import config


class FileHandler:
    """Handles file operations for the translation API"""

    @staticmethod
    def calculate_sha256(file_path: Path) -> Optional[str]:
        """
        Calculate the SHA256 hash of a file

        Args:
            file_path: Path to the file

        Returns:
            SHA256 hash string or None if error
        """
        try:
            if not file_path.exists():
                return None
            sha256_hash = hashlib.sha256()
            with open(file_path, "rb") as f:
                for byte_block in iter(lambda: f.read(4096), b""):
                    sha256_hash.update(byte_block)
            return sha256_hash.hexdigest()
        except Exception as e:
            import logging

            logging.getLogger(__name__).error(
                f"SHA256 calculation failed for {file_path}: {e}"
            )
            return None

    @staticmethod
    def validate_file_extension(filename: str) -> str:
        """
        Validate that the file extension is supported

        Args:
            filename: Name of the file

        Returns:
            File extension (lowercase, with dot)

        Raises:
            HTTPException: If file extension is not supported
        """
        file_extension = Path(filename).suffix.lower()

        if file_extension not in config.SUPPORTED_EXTENSIONS:
            raise HTTPException(
                status_code=400,
                detail=f"Unsupported file type. Supported types: {', '.join(config.SUPPORTED_EXTENSIONS)}",
            )

        return file_extension

    @staticmethod
    def validate_file_size(file: UploadFile) -> None:
        """
        Validate that the file size is within limits

        Args:
            file: Uploaded file

        Raises:
            HTTPException: If file is too large
        """
        # Get file size
        file.file.seek(0, 2)  # Move to end of file
        file_size = file.file.tell()  # Get position (file size)
        file.file.seek(0)  # Reset to beginning

        if file_size > config.MAX_FILE_SIZE_BYTES:
            raise HTTPException(
                status_code=400,
                detail=f"File too large. Maximum size: {config.MAX_FILE_SIZE_MB}MB",
            )

    @staticmethod
    async def save_upload_file(file: UploadFile, destination: Path, chunk_size: int = 65536) -> Path:
        """
        Save an uploaded file to disk using chunked streaming to avoid loading
        the entire file into memory at once.

        Args:
            file: Uploaded file
            destination: Path to save the file
            chunk_size: Read/write chunk size in bytes (default 64KB)

        Returns:
            Path to the saved file
        """
        destination.parent.mkdir(parents=True, exist_ok=True)

        with open(destination, "wb") as buffer:
            while True:
                chunk = await file.read(chunk_size)
                if not chunk:
                    break
                buffer.write(chunk)

        return destination

    @staticmethod
    def generate_unique_filename(original_filename: str, prefix: str = "") -> str:
        """
        Generate a unique filename to avoid collisions

        Args:
            original_filename: Original filename
            prefix: Optional prefix for the filename

        Returns:
            Unique filename
        """
        file_path = Path(original_filename)
        unique_id = str(uuid.uuid4())[:8]

        if prefix:
            return f"{prefix}_{unique_id}_{file_path.stem}{file_path.suffix}"
        else:
            return f"{unique_id}_{file_path.stem}{file_path.suffix}"

    @staticmethod
    def cleanup_file(file_path: Path) -> None:
        """
        Delete a file if it exists

        Args:
            file_path: Path to the file to delete
        """
        import logging

        _logger = logging.getLogger(__name__)
        try:
            if file_path.exists():
                file_path.unlink()
                _logger.debug(f"Deleted file: {file_path}")
        except Exception as e:
            _logger.warning(f"Error deleting file {file_path}: {e}")

    @staticmethod
    def get_file_info(file_path: Path) -> dict:
        """
        Get information about a file

        Args:
            file_path: Path to the file

        Returns:
            Dictionary with file information
        """
        if not file_path.exists():
            return {}

        stat = file_path.stat()

        return {
            "filename": file_path.name,
            "size_bytes": stat.st_size,
            "size_mb": round(stat.st_size / (1024 * 1024), 2),
            "sha256": FileHandler.calculate_sha256(file_path),
            "extension": file_path.suffix,
            "created": stat.st_ctime,
            "modified": stat.st_mtime,
        }


# Global file handler instance
file_handler = FileHandler()


def validate_zip_safety(
    file_path: Path,
    max_compression_ratio: float = 100.0,
    max_total_uncompressed_mb: int = 1024,
) -> None:
    """Reject ZIP-based documents that expand dangerously (zip bombs).

    Office files (.xlsx/.docx/.pptx) are ZIP archives: a small uploaded file
    can decompress to gigabytes in memory. Raises ValueError when the file
    is not a readable archive, expands beyond the allowed ratio, or when the
    total uncompressed size exceeds the cap.
    """
    import zipfile

    max_total_bytes = max_total_uncompressed_mb * 1024 * 1024
    try:
        with zipfile.ZipFile(file_path) as zf:
            total_uncompressed = 0
            for info in zf.infolist():
                if info.is_dir():
                    continue
                total_uncompressed += info.file_size
                if (
                    info.compress_size > 0
                    and info.file_size / info.compress_size > max_compression_ratio
                ):
                    raise ValueError(
                        f"Entry '{info.filename}' expands more than "
                        f"{int(max_compression_ratio)}x its compressed size."
                    )
                if total_uncompressed > max_total_bytes:
                    raise ValueError(
                        f"Archive expands beyond {max_total_uncompressed_mb} MB."
                    )
    except zipfile.BadZipFile as e:
        raise ValueError(f"Not a valid ZIP-based document: {e}")