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// libovgu-canteen - A canteen parser module for ovgu.
//
// Copyright (C) 2017
//     Fin Christensen <christensen.fin@gmail.com>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

use crate::{Day, Error, FromElement, Update};
use serde::{Serialize, Deserialize};
use futures::TryStreamExt;
use hyper;
use hyper_tls;
use scraper;
use std;
use std::clone::Clone;

/// A canteen holds all the meals on all available days.
#[derive(Serialize, Deserialize, Debug)]
pub struct Canteen {
    /// This identifies a canteen.
    pub description: CanteenDescription,

    /// All available days holding the meals for this canteen.
    pub days: Vec<Day>,
}

/// This enum identifies a canteen.
#[derive(Serialize, Deserialize, Debug, PartialEq, Hash, Eq, Clone)]
pub enum CanteenDescription {
    /// Mensa UniCampus Magdeburg lower hall
    UniCampusLowerHall,

    /// Mensa UniCampus Magdeburg upper hall
    UniCampusUpperHall,

    /// Mensa Kellercafé Magdeburg
    Kellercafe,

    /// Mensa Herrenkrug Magdeburg
    Herrenkrug,

    /// Mensa Stendal
    Stendal,

    /// Mensa Wernigerode
    Wernigerode,

    /// Mensa DomCafete Halberstadt
    DomCafeteHalberstadt,
}

impl Canteen {
    /// This method creates a new canteen instance from a given description.
    ///
    /// # Arguments
    ///
    /// * `desc`  - The identifier identifying the canteen.
    ///
    /// # Examples
    ///
    /// Create a new canteen:
    ///
    /// ```
    /// use ovgu_canteen::{Canteen, CanteenDescription};
    /// # #[tokio::main]
    /// # async fn main() {
    /// let canteen = Canteen::new(CanteenDescription::UniCampusLowerHall).await.unwrap();
    /// println!("{}", canteen.days[0].meals[0].name);
    /// # }
    /// ```
    pub async fn new(desc: CanteenDescription) -> Result<Self, Error> {
        let days = Self::load(desc.clone()).await?;
        Ok(Canteen {
            description: desc,
            days: days,
        })
    }

    /// This method updates the canteen from the website.
    pub async fn update(&mut self) -> Result<(), Error> {
        let days = Self::load(self.description.clone()).await?;

        self.merge(Canteen {
            description: self.description.clone(),
            days,
        })
    }

    /// This method merges this canteen with another canteen.
    ///
    /// Both canteens must contain the same description, otherwise a
    /// `CouldNotMerge` error is given.
    pub fn merge(&mut self, other: Canteen) -> Result<(), Error> {
        if self.description != other.description {
            return Err(Error::CouldNotMerge {
                us: self.description.clone(),
                them: other.description,
            });
        }

        for day in other.days.iter() {
            if match self.days.iter_mut().find(|d| *d == day) {
                Some(ref mut d) => {
                    d.update(day)?;
                    false
                }
                None => true,
            }
            {
                self.days.push(day.clone());
            }
        }

        self.days.sort_by_key(|day| day.date);

        Ok(())
    }

    async fn load(desc: CanteenDescription) -> Result<Vec<Day>, Error> {
        let connector = hyper_tls::HttpsConnector::new();
        let client = hyper::Client::builder().build::<_, hyper::Body>(connector);

        let url = match desc {
            CanteenDescription::UniCampusLowerHall => ovgu_canteen_url![uni_campus_lower_hall],
            CanteenDescription::UniCampusUpperHall => ovgu_canteen_url![uni_campus_upper_hall],
            CanteenDescription::Kellercafe => ovgu_canteen_url![kellercafe],
            CanteenDescription::Herrenkrug => ovgu_canteen_url![herrenkrug],
            CanteenDescription::Stendal => ovgu_canteen_url![stendal],
            CanteenDescription::Wernigerode => ovgu_canteen_url![wernigerode],
            CanteenDescription::DomCafeteHalberstadt => ovgu_canteen_url![dom_cafete_halberstadt],
        };
        // this can't fail as it is based on a constant defined in this crate
        let uri = url.parse().unwrap();

        let mut resp = client.get(uri).await
            .map_err(|cause| Error::Fetch { url: url.to_string(), cause })?;
        let chunks: Vec<_> = resp.body_mut().try_collect().await
            .map_err(|cause| Error::Fetch { url: url.to_string(), cause })?;
        let bytes = chunks.concat();
        let body = std::str::from_utf8(&bytes)
            .map_err(|cause| Error::ResponseEncoding { cause })?;

        scraper::Html::parse_document(&body)
            .select(&ovgu_canteen_selector![day])
            .map(|day_node| Day::from_element(&day_node))
            .collect::<Result<Vec<Day>, Error>>()
    }
}

impl PartialEq for Canteen {
    fn eq(&self, other: &Self) -> bool {
        self.description == other.description
    }
}