from pathlib import Path

from fastapi import HTTPException, UploadFile, status

ALLOWED_DATASET_EXTENSIONS = {".csv", ".xlsx", ".xls"}


def get_file_extension(filename: str) -> str:
    return Path(filename).suffix.lower()


def validate_supported_dataset_file(file: UploadFile) -> str:
    if not file.filename:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Uploaded file must include a filename.",
        )

    extension = get_file_extension(file.filename)
    if extension not in ALLOWED_DATASET_EXTENSIONS:
        allowed = ", ".join(sorted(ALLOWED_DATASET_EXTENSIONS))
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail=f"Unsupported file type. Allowed file types: {allowed}.",
        )

    return extension


def validate_file_size(file_size_bytes: int, max_size_bytes: int) -> None:
    if file_size_bytes <= 0:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Uploaded file is empty.",
        )

    if file_size_bytes > max_size_bytes:
        max_size_display = (
            f"{max_size_bytes / (1024 * 1024):.0f} MB"
            if max_size_bytes >= 1024 * 1024
            else f"{max_size_bytes} bytes"
        )
        raise HTTPException(
            status_code=status.HTTP_413_REQUEST_ENTITY_TOO_LARGE,
            detail=f"Uploaded file is too large. Maximum size is {max_size_display}.",
        )