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

use std::collections::HashMap;

use reqwest::header::HeaderMap;
use scraper::{Html, Selector};

use crate::results::aggregation_models::SearchResult;

use super::engine_models::{EngineError, SearchEngine};

use error_stack::{Report, Result, ResultExt};

/// A new DuckDuckGo 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 DuckDuckGo;

#[async_trait::async_trait]
impl SearchEngine for DuckDuckGo {
    /// 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.
    /// * `request_timeout` - Takes a time (secs) as a value which controls the server request timeout.
    ///
    /// # 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: &str,
        page: u32,
        user_agent: &str,
        request_timeout: u8,
        _safe_search: u8,
    ) -> Result<HashMap<String, SearchResult>, 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 {
            1 | 0 => {
                format!("https://html.duckduckgo.com/html/?q={query}&s=&dc=&v=1&o=json&api=/d.js")
            }
            _ => {
                format!(
                    "https://duckduckgo.com/html/?q={}&s={}&dc={}&v=1&o=json&api=/d.js",
                    query,
                    (page / 2 + (page % 2)) * 30,
                    (page / 2 + (page % 2)) * 30 + 1
                )
            }
        };

        // initializing HeaderMap and adding appropriate headers.
        let header_map = HeaderMap::try_from(&HashMap::from([
            ("USER_AGENT".to_string(), user_agent.to_string()),
            ("REFERER".to_string(), "https://google.com/".to_string()),
            (
                "CONTENT_TYPE".to_string(),
                "application/x-www-form-urlencoded".to_string(),
            ),
            ("COOKIE".to_string(), "kl=wt-wt".to_string()),
        ]))
        .change_context(EngineError::UnexpectedError)?;

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

        let no_result: Selector = Selector::parse(".no-results")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".no-results"))?;

        if document.select(&no_result).next().is_some() {
            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(".result__a")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".result__a"))?;
        let result_url: Selector = Selector::parse(".result__url")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".result__url"))?;
        let result_desc: Selector = Selector::parse(".result__snippet")
            .map_err(|_| Report::new(EngineError::UnexpectedError))
            .attach_printable_lazy(|| format!("invalid CSS selector: {}", ".result__snippet"))?;

        // scrape all the results from the html
        Ok(document
            .select(&results)
            .map(|result| {
                SearchResult::new(
                    result
                        .select(&result_title)
                        .next()
                        .unwrap()
                        .inner_html()
                        .trim(),
                    format!(
                        "https://{}",
                        result
                            .select(&result_url)
                            .next()
                            .unwrap()
                            .inner_html()
                            .trim()
                    )
                    .as_str(),
                    result
                        .select(&result_desc)
                        .next()
                        .unwrap()
                        .inner_html()
                        .trim(),
                    &["duckduckgo"],
                )
            })
            .map(|search_result| (search_result.url.clone(), search_result))
            .collect())
    }
}