from urllib2 import urlopen
from bs4 import BeautifulSoup

# Get the next page url from the current page url
def get_next_page_url(url):
    page = urlopen(url)
    soup_page = BeautifulSoup(page, ‘lxml‘)
    page.close()
    # Get current page and next page tag
    current_page_tag = soup_page.find(class_="current")
    next_page_tag = current_page_tag.find_next_sibling()
    # Check if the current page is the last one
    if next_page_tag is None:
        next_page_url = None
    else:
        next_page_url = next_page_tag[‘href‘]
    return next_page_url 

# Get the book detail urls by page url 
def get_book_detail_urls(url):
    page = urlopen(url)
    soup = BeautifulSoup(page, ‘lxml‘)
    page.close()
    urls = []
    book_header_tags = soup.find_all(class_="entry-title")
    for book_header_tag in book_header_tags:
        urls.append(book_header_tag.a[‘href‘])
    return urls
    

# Get the book detail info by book detail url
def get_book_isbn(url):
    page = urlopen(url)
    book_isbn_soup = BeautifulSoup(page, ‘lxml‘)
    page.close()
    title_tag = book_isbn_soup.find(class_="single-title")
    title = title_tag.string
    isbn_key_tag = book_isbn_soup.find(text="ISBN-10:").parent
    isbn_tag = isbn_key_tag.find_next_sibling()
    isbn = isbn_tag.string.strip() # Remove the whitespace with the strip method
    return { ‘title‘: title, ‘ISBN‘: isbn }

def start():
    url = "http://www.allitebooks.com/certification/"
    book_info_list = []
    def next_page(page_url):
        book_detail_urls = get_book_detail_urls(page_url)
        for book_detail_url in book_detail_urls: #print all books ISBN one by one
            # print(book_detail_url)
            book_info = get_book_isbn(book_detail_url)
            print(book_info)   # print ISBD
            book_info_list.append(book_info)
        next_page_url = get_next_page_url(page_url)
        if next_page_url is not None:
            next_page(next_page_url)
        else:
            return 0
    next_page(url)