from numpy import array, ndarray
import pdf2image
from PIL import Image
import cv2


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


def open_pdf(pdf, first_page=0, last_page=None):
    
    first_page += 1
    last_page = None if last_page is None else last_page + 1
    
    if type(pdf) == str:
        if pdf.lower().endswith((".png", ".jpg", ".jpeg")):
            pages = [Image.open(pdf)]
        else: # assume pdf as default file type for a path argument
            pages = pdf2image.convert_from_path(pdf, first_page=first_page, last_page=last_page)
    elif type(pdf) == bytes:
        pages = pdf2image.convert_from_bytes(pdf, first_page=first_page, last_page=last_page)
    elif type(pdf) in {list, ndarray}:
        return pdf
    
    pages = [preprocess_pdf_image(array(p)) for p in pages]
    
    return pages