//! The `searx` module handles the scraping of results from the searx search engine instance
//! by querying the upstream searx search engine instance with user provided query and with a page
//! number if provided.

use reqwest::header::{HeaderMap, CONTENT_TYPE, COOKIE, REFERER, USER_AGENT};
use scraper::{Html, Selector};
use std::collections::HashMap;

use crate::results::aggregation_models::RawSearchResult;

use super::engine_models::{EngineError, SearchEngine};
use error_stack::{IntoReport, Report, Result, ResultExt};

/// A new Searx engine type defined in-order to implement the `SearchEngine` trait which allows to
/// reduce code duplication as well as allows to create vector of different search engines easily.
pub struct Searx;

#[async_trait::async_trait]
impl SearchEngine for Searx {
    /// This function scrapes results from the upstream engine duckduckgo and puts all the scraped
    /// results like title, visiting_url (href in html),engine (from which engine it was fetched from)
    /// and description in a RawSearchResult and then adds that to HashMap whose keys are url and
    /// values are RawSearchResult struct and then returns it within a Result enum.
    ///
    /// # Arguments
    ///
    /// * `query` - Takes the user provided query to query to the upstream search engine with.
    /// * `page` - Takes an u32 as an argument.
    /// * `user_agent` - Takes a random user agent string as an argument.
    ///
    /// # Errors
    ///
    /// Returns an `EngineErrorKind` if the user is not connected to the internet or if their is failure to
    /// reach the above `upstream search engine` page or if the `upstream search engine` is unable to
    /// provide results for the requested search query and also returns error if the scraping selector
    /// or HeaderMap fails to initialize.

    async fn results(
        &self,
        query: String,
        page: u32,
        user_agent: String,
    ) -> Result<HashMap<String, RawSearchResult>, EngineError> {
        // Page number can be missing or empty string and so appropriate handling is required
        // so that upstream server recieves valid page number.
        let url: String = match page {
            0 | 1 => format!("https://searx.work/search?q={query}&pageno=1"),
            _ => format!("https://searx.work/search?q={query}&pageno={page}"),
        };

        // initializing headers and adding appropriate headers.
        let mut header_map = HeaderMap::new();
        header_map.insert(
            USER_AGENT,
            user_agent
                .parse()
                .into_report()
                .change_context(EngineError::UnexpectedError)?,
        );
        header_map.insert(
            REFERER,
            "https://google.com/"
                .parse()
                .into_report()
                .change_context(EngineError::UnexpectedError)?,
        );
        header_map.insert(
            CONTENT_TYPE,
            "application/x-www-form-urlencoded"
                .parse()
                .into_report()
                .change_context(EngineError::UnexpectedError)?,
        );
        header_map.insert(COOKIE, "categories=general; language=auto; locale=en; autocomplete=duckduckgo; image_proxy=1; method=POST; safesearch=2; theme=simple; results_on_new_tab=1; doi_resolver=oadoi.org; simple_style=auto; center_alignment=1; query_in_title=1; infinite_scroll=0; disabled_engines=; enabled_engines=\"archive is__general\\054yep__general\\054curlie__general\\054currency__general\\054ddg definitions__general\\054wikidata__general\\054duckduckgo__general\\054tineye__general\\054lingva__general\\054startpage__general\\054yahoo__general\\054wiby__general\\054marginalia__general\\054alexandria__general\\054wikibooks__general\\054wikiquote__general\\054wikisource__general\\054wikiversity__general\\054wikivoyage__general\\054dictzone__general\\054seznam__general\\054mojeek__general\\054naver__general\\054wikimini__general\\054brave__general\\054petalsearch__general\\054goo__general\"; disabled_plugins=; enabled_plugins=\"searx.plugins.hostname_replace\\054searx.plugins.oa_doi_rewrite\\054searx.plugins.vim_hotkeys\"; tokens=; maintab=on; enginetab=on".parse().into_report().change_context(EngineError::UnexpectedError)?);

        let document: Html =
            Html::parse_document(&Searx::fetch_html_from_upstream(self, url, header_map).await?);

        let no_result: Selector = Selector::parse("#urls>.dialog-error>p")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| {
                format!("invalid CSS selector: {}", "#urls>.dialog-error>p")
            })?;

        if let Some(no_result_msg) = document.select(&no_result).nth(1) {
            if no_result_msg.inner_html()
            == "we didn't find any results. Please use another query or search in more categories"
        {
            return Err(Report::new(EngineError::EmptyResultSet));
        }
        }

        let results: Selector = Selector::parse(".result")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".result"))?;
        let result_title: Selector = Selector::parse("h3>a")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", "h3>a"))?;
        let result_url: Selector = Selector::parse("h3>a")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", "h3>a"))?;

        let result_desc: Selector = Selector::parse(".content")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".content"))?;

        // scrape all the results from the html
        Ok(document
            .select(&results)
            .map(|result| {
                RawSearchResult::new(
                    result
                        .select(&result_title)
                        .next()
                        .unwrap()
                        .inner_html()
                        .trim()
                        .to_string(),
                    result
                        .select(&result_url)
                        .next()
                        .unwrap()
                        .value()
                        .attr("href")
                        .unwrap()
                        .to_string(),
                    result
                        .select(&result_desc)
                        .next()
                        .unwrap()
                        .inner_html()
                        .trim()
                        .to_string(),
                    vec!["searx".to_string()],
                )
            })
            .map(|search_result| (search_result.visiting_url.clone(), search_result))
            .collect())
    }
}