"""
Shared utility functions for the Puff n Parse backend.
"""
import os
import uuid
import tempfile
from pathlib import Path


# Temporary upload directory — ephemeral, cleaned after processing
UPLOAD_DIR = Path(tempfile.gettempdir()) / "puffnparse_uploads"
UPLOAD_DIR.mkdir(parents=True, exist_ok=True)

# Maximum file sizes
MAX_FILE_SIZE_UNREGISTERED = 10 * 1024 * 1024  # 10MB
MAX_FILE_SIZE_REGISTERED = 50 * 1024 * 1024     # 50MB (placeholder)

# Supported MIME types and their corresponding FileType
SUPPORTED_MIME_TYPES = {
    "application/pdf": "pdf",
    "image/jpeg": "jpeg",
    "image/jpg": "jpeg",
    "image/png": "png",
}

SUPPORTED_EXTENSIONS = {".pdf", ".jpg", ".jpeg", ".png"}


def generate_temp_filename(original_filename: str) -> str:
    """Generate a unique temporary filename preserving the extension."""
    ext = Path(original_filename).suffix.lower()
    return f"{uuid.uuid4().hex}{ext}"


def get_file_extension(filename: str) -> str:
    """Extract and normalise the file extension."""
    return Path(filename).suffix.lower()


def validate_file_type(filename: str, content_type: str | None) -> str | None:
    """
    Validate the uploaded file type.
    Returns the normalised type string ('pdf', 'jpeg', 'png') or None if invalid.
    """
    ext = get_file_extension(filename)
    if ext not in SUPPORTED_EXTENSIONS:
        return None

    # Normalise jpeg/jpg
    if ext in {".jpg", ".jpeg"}:
        return "jpeg"
    return ext.lstrip(".")


def cleanup_temp_file(filepath: str | Path) -> None:
    """Safely remove a temporary file."""
    try:
        path = Path(filepath)
        if path.exists():
            path.unlink()
    except OSError:
        pass  # Best-effort cleanup


def format_file_size(size_bytes: int) -> str:
    """Format bytes into a human-readable string."""
    if size_bytes < 1024:
        return f"{size_bytes} B"
    elif size_bytes < 1024 * 1024:
        return f"{size_bytes / 1024:.1f} KB"
    else:
        return f"{size_bytes / (1024 * 1024):.1f} MB"