import io
import fitz  # PyMuPDF


def pdf_to_image_bytes(pdf_bytes: bytes, dpi: int = 200) -> bytes:
    """Render the first page of a PDF to JPEG bytes."""
    doc = fitz.open(stream=pdf_bytes, filetype="pdf")
    if doc.page_count == 0:
        raise ValueError("The uploaded PDF has no pages.")

    page = doc.load_page(0)
    mat = fitz.Matrix(dpi / 72, dpi / 72)
    pix = page.get_pixmap(matrix=mat, colorspace=fitz.csRGB)

    buffer = io.BytesIO(pix.tobytes("jpeg"))
    return buffer.getvalue()