# Source code for searx.engines.google_scholar

    # SPDX-License-Identifier: AGPL-3.0-or-later
    """This is the implementation of the Google Scholar engine.

    Compared to other Google services the Scholar engine has a simple GET REST-API
    and there does not exists `async` API.  Even though the API slightly vintage we
    can make use of the :ref:`google API` to assemble the arguments of the GET
    request.
    """

    from typing import TYPE_CHECKING
    from typing import Optional

    from urllib.parse import urlencode
    from datetime import datetime
    from lxml import html

    from searx.utils import (
        eval_xpath,
        eval_xpath_getindex,
        eval_xpath_list,
        extract_text,
    )

    from searx.exceptions import SearxEngineCaptchaException

    from searx.engines.google import fetch_traits  # pylint: disable=unused-import
    from searx.engines.google import (
        get_google_info,
        time_range_dict,
    )
    from searx.enginelib.traits import EngineTraits

    if TYPE_CHECKING:
        import logging

        logger: logging.Logger

    traits: EngineTraits

    # about
    about = {
        "website": 'https://scholar.google.com',
        "wikidata_id": 'Q494817',
        "official_api_documentation": 'https://developers.google.com/custom-search',
        "use_official_api": False,
        "require_api_key": False,
        "results": 'HTML',
    }

    # engine dependent config
    categories = ['science', 'scientific publications']
    paging = True
    max_page = 50
    language_support = True
    time_range_support = True
    safesearch = False
    send_accept_language_header = True

    def time_range_args(params):
        """Returns a dictionary with a time range arguments based on
        ``params['time_range']``.

        Google Scholar supports a detailed search by year.  Searching by *last
        month* or *last week* (as offered by SearXNG) is uncommon for scientific
        publications and is not supported by Google Scholar.

        To limit the result list when the users selects a range, all the SearXNG
        ranges (*day*, *week*, *month*, *year*) are mapped to *year*.  If no range
        is set an empty dictionary of arguments is returned.  Example;  when
        user selects a time range (current year minus one in 2022):

        .. code:: python

            { 'as_ylo' : 2021 }

        """
        ret_val = {}
        if params['time_range'] in time_range_dict:
            ret_val['as_ylo'] = datetime.now().year - 1
        return ret_val

    def detect_google_captcha(dom):
        """In case of CAPTCHA Google Scholar open its own *not a Robot* dialog and is
        not redirected to ``sorry.google.com``.
        """
        if eval_xpath(dom, "//form[@id='gs_captcha_f']"):
            raise SearxEngineCaptchaException()

    def request(query, params):
        """Google-Scholar search request"""

        google_info = get_google_info(params, traits)
        # subdomain is: scholar.google.xy
        google_info['subdomain'] = google_info['subdomain'].replace("www.", "scholar.")

        args = {
            'q': query,
            **google_info['params'],
            'start': (params['pageno'] - 1) * 10,
            'as_sdt': '2007',  # include patents / to disable set '0,5'
            'as_vis': '0',  # include citations / to disable set '1'
        }
        args.update(time_range_args(params))

        params['url'] = 'https://' + google_info['subdomain'] + '/scholar?' + urlencode(args)
        params['cookies'] = google_info['cookies']
        params['headers'].update(google_info['headers'])
        return params

    def parse_gs_a(text: Optional[str]):
        """Parse the text written in green.

        Possible formats:
        * "{authors} - {journal}, {year} - {publisher}"
        * "{authors} - {year} - {publisher}"
        * "{authors} - {publisher}"
        """
        if text is None or text == "":
            return None, None, None, None

        s_text = text.split(' - ')
        authors = s_text[0].split(', ')
        publisher = s_text[-1]
        if len(s_text) != 3:
            return authors, None, publisher, None

        # the format is "{authors} - {journal}, {year} - {publisher}" or "{authors} - {year} - {publisher}"
        # get journal and year
        journal_year = s_text[1].split(', ')
        # journal is optional and may contains some coma
        if len(journal_year) > 1:
            journal = ', '.join(journal_year[0:-1])
            if journal == '…':
                journal = None
        else:
            journal = None
        # year
        year = journal_year[-1]
        try:
            publishedDate = datetime.strptime(year.strip(), '%Y')
        except ValueError:
            publishedDate = None
        return authors, journal, publisher, publishedDate

    def response(resp):  # pylint: disable=too-many-locals
        """Parse response from Google Scholar"""
        results = []

        # convert the text to dom
        dom = html.fromstring(resp.text)
        detect_google_captcha(dom)

        # parse results
        for result in eval_xpath_list(dom, '//div[@data-rp]'):

            title = extract_text(eval_xpath(result, './/h3[1]//a'))

            if not title:
                # this is a [ZITATION] block
                continue

            pub_type = extract_text(eval_xpath(result, './/span[@class="gs_ctg2"]'))
            if pub_type:
                pub_type = pub_type[1:-1].lower()

            url = eval_xpath_getindex(result, './/h3[1]//a/@href', 0)
            content = extract_text(eval_xpath(result, './/div[@class="gs_rs"]'))
            authors, journal, publisher, publishedDate = parse_gs_a(
                extract_text(eval_xpath(result, './/div[@class="gs_a"]'))
            )
            if publisher in url:
                publisher = None

            # cited by
            comments = extract_text(eval_xpath(result, './/div[@class="gs_fl"]/a[starts-with(@href,"/scholar?cites=")]'))

            # link to the html or pdf document
            html_url = None
            pdf_url = None
            doc_url = eval_xpath_getindex(result, './/div[@class="gs_or_ggsm"]/a/@href', 0, default=None)
            doc_type = extract_text(eval_xpath(result, './/span[@class="gs_ctg2"]'))
            if doc_type == "[PDF]":
                pdf_url = doc_url
            else:
                html_url = doc_url

            results.append(
                {
                    'template': 'paper.html',
                    'type': pub_type,
                    'url': url,
                    'title': title,
                    'authors': authors,
                    'publisher': publisher,
                    'journal': journal,
                    'publishedDate': publishedDate,
                    'content': content,
                    'comments': comments,
                    'html_url': html_url,
                    'pdf_url': pdf_url,
                }
            )

        # parse suggestion
        for suggestion in eval_xpath(dom, '//div[contains(@class, "gs_qsuggest_wrap")]//li//a'):
            # append suggestion
            results.append({'suggestion': extract_text(suggestion)})

        for correction in eval_xpath(dom, '//div[@class="gs_r gs_pda"]/a'):
            results.append({'correction': extract_text(correction)})

        return results