from numpy import frombuffer, ndarray
import cv2


def preprocess_page_array(page):
    if len(page.shape) > 2:
        page = cv2.cvtColor(page, cv2.COLOR_BGR2GRAY)
    page = cv2.fastNlMeansDenoising(page, h=3)
    return page


def page2image(page):

    if type(page) == bytes:
        page = frombuffer(page)
    elif type(page) == ndarray:
        page = page
    elif type(page) == str:
        if page.lower().endswith((".png", ".jpg", ".jpeg")):
            page = cv2.imread(page)
        else:
            raise IOError(
                "PDFs are not a valid input type for cv-analysis."
                " Use PNGs for tests and NumPy arrays for deployment."
            )
    else:
        raise TypeError("Incompatible datatype. Expected bytes, numpy.ndarray, or path to an image file.")

    return preprocess_page_array(page)