class Pagination(object):
    def __init__(self,current_page,all_count,per_page_num=2,pager_count=11):
        """
        封裝分頁相關資料
        :param current_page: 當前頁
        :param all_count:    資料庫中的資料總條數
        :param per_page_num: 每頁顯示的資料條數
        :param pager_count:  最多顯示的頁碼個數
        
        用法:
        queryset = model.objects.all()
        page_obj = Pagination(current_page,all_count)
        page_data = queryset[page_obj.start:page_obj.end]
        獲取資料用page_data而不再使用原始的queryset
        獲取前端分頁樣式用page_obj.page_html
        """
        try:
            current_page = int(current_page)
        except Exception as e:
            current_page = 1

        if current_page <1:
            current_page = 1

        self.current_page = current_page

        self.all_count = all_count
        self.per_page_num = per_page_num


        # 總頁碼
        all_pager, tmp = divmod(all_count, per_page_num)
        if tmp:
            all_pager += 1
        self.all_pager = all_pager

        self.pager_count = pager_count
        self.pager_count_half = int((pager_count - 1) / 2)

    @property
    def start(self):
        return (self.current_page - 1) * self.per_page_num

    @property
    def end(self):
        return self.current_page * self.per_page_num

    def page_html(self):
        # 如果總頁碼 < 11個：
        if self.all_pager <= self.pager_count:
            pager_start = 1
            pager_end = self.all_pager + 1
        # 總頁碼  > 11
        else:
            # 當前頁如果<=頁面上最多顯示11/2個頁碼
            if self.current_page <= self.pager_count_half:
                pager_start = 1
                pager_end = self.pager_count + 1

            # 當前頁大於5
            else:
                # 頁碼翻到最後
                if (self.current_page + self.pager_count_half) > self.all_pager:
                    pager_end = self.all_pager + 1
                    pager_start = self.all_pager - self.pager_count + 1
                else:
                    pager_start = self.current_page - self.pager_count_half
                    pager_end = self.current_page + self.pager_count_half + 1

        page_html_list = []
        # 新增前面的nav和ul標籤
        page_html_list.append('''
                    <nav aria-label='Page navigation>'
                    <ul class='pagination'>
                ''')
        first_page = '<li><a href="?page=%s">首頁</a></li>' % (1)
        page_html_list.append(first_page)

        if self.current_page <= 1:
            prev_page = '<li class="disabled"><a href="#">上一頁</a></li>'
        else:
            prev_page = '<li><a href="?page=%s">上一頁</a></li>' % (self.current_page - 1,)

        page_html_list.append(prev_page)

        for i in range(pager_start, pager_end):
            if i == self.current_page:
                temp = '<li class="active"><a href="?page=%s">%s</a></li>' % (i, i,)
            else:
                temp = '<li><a href="?page=%s">%s</a></li>' % (i, i,)
            page_html_list.append(temp)

        if self.current_page >= self.all_pager:
            next_page = '<li class="disabled"><a href="#">下一頁</a></li>'
        else:
            next_page = '<li><a href="?page=%s">下一頁</a></li>' % (self.current_page + 1,)
        page_html_list.append(next_page)

        last_page = '<li><a href="?page=%s">尾頁</a></li>' % (self.all_pager,)
        page_html_list.append(last_page)
        # 尾部新增標籤
        page_html_list.append('''
                                           </nav>
                                           </ul>
                                       ''')
        return ''.join(page_html_list)