import json,logging
from scrapy.loader import ItemLoader

class ComicLoader(ItemLoader):
    def parseExec(cls,data,exec):
        if data !=None and exec != None:
            dots = str(exec).split(".")
            if not isinstance(data,dict): data = json.loads(data)
            for dot in dots:
                data = data.get(dot)
        return data

    def add_xpath(self, field_name, xpath, *processors, index=None, exec=None, re=None, is_null=None, **kw):
        """
        Similar to :meth:`ItemLoader.add_value` but receives an XPath instead of a
        value, which is used to extract a list of strings from the
        selector associated with this :class:`ItemLoader`.

        See :meth:`get_xpath` for ``kwargs``.

        :param xpath: the XPath to extract data from
        :type xpath: str

        Examples::

            # HTML snippet: <p class="product-name">Color TV</p>
            loader.add_xpath('name', '//p[@class="product-name"]')
            # HTML snippet: <p id="price">the price is $1200</p>
            loader.add_xpath('price', '//p[@id="price"]', re='the price is (.*)')

        """
        values = self._get_xpathvalues(xpath, **kw)
        if exec is not None:
            values = self.parseExec(values, exec)
        if index is not None:
            if len(values) - 1 >= index:
                try:
                    values = values[index]
                except Exception as e:
                    logging.error(f"values [{values}] error index [{index}]")
                    logging.error(e)
            else:
                if is_null is not None: values = is_null
                else: values=""
        self.add_value(field_name, values, *processors, re=re, **kw)

    def add_exec(self, field_name, value, str_exec=None, *processors, re=None, **kw):
        if str_exec is not None:
            value = self.parseExec(value, str_exec)
        self.add_value(field_name, value, *processors, re=re, **kw)

    def get_exec(self, value, str_exec):
        return self.parseExec(value, str_exec)
   
    def add_value(self, field_name, value, *processors, re=None, **kw):
        if self.auto_replace_value(field_name, value):
            return super().add_value(field_name, value, *processors, re=re, **kw)
    
     
    def auto_replace_value(self, field_name, value):
        if self.get_output_value(field_name) != None:
            self._replace_value(field_name, value)
            return False 
        else: return True