// bebot
// Copyright (C) 2023 Brian Tarricone <brian@tarricone.org>
//
// 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 std::{
    fmt,
    io::{BufReader, BufWriter, ErrorKind},
    path::PathBuf,
    time::{Duration, SystemTime},
};

use anyhow::Context;
use chrono::{DateTime, Utc};
use futures::{future::join_all, FutureExt};
use matrix_sdk::{
    ruma::{events::room::message::RoomMessageEventContent, OwnedRoomOrAliasId},
    Client,
};
use reqwest::redirect;
use serde::de;
use tokio::{fs::File, task::JoinHandle, time::sleep};

use crate::{
    config::{MailArchiveConfig, MailListConfig},
    matrix,
};

#[derive(Clone, Copy, Serialize, Deserialize)]
struct ListState {
    last_pub_date: DateTime<Utc>,
}

#[derive(Debug, Deserialize)]
struct RssPubDate {
    #[serde(rename = "$text", deserialize_with = "deser_rfc2616")]
    value: DateTime<Utc>,
}

#[derive(Debug, Deserialize)]
struct RssItem {
    title: String,
    link: String,
    #[serde(rename = "pubDate")]
    pub_date: RssPubDate,
}

#[derive(Debug, Deserialize)]
struct RssChannel {
    #[serde(rename = "item")]
    items: Vec<RssItem>,
}

#[derive(Debug, Deserialize)]
struct MailRss {
    channel: RssChannel,
}

async fn load_list_state(state_file: &PathBuf) -> anyhow::Result<ListState> {
    match File::open(state_file).await {
        Err(err) if err.kind() == ErrorKind::NotFound => {
            // If we have no state, we probably don't want to blast out events
            // for every single item in the RSS feed, so pretend the last time
            // we published was right now.
            let list_state = ListState {
                last_pub_date: SystemTime::now().into(),
            };
            save_list_state(list_state, state_file).await?;
            Ok(list_state)
        }
        Err(err) => Err(err)?,
        Ok(f) => {
            let r = BufReader::new(f.into_std().await);
            Ok(tokio::task::spawn_blocking(move || serde_yaml::from_reader(r)).await??)
        }
    }
}

async fn save_list_state(list_state: ListState, state_file: &PathBuf) -> anyhow::Result<()> {
    let f = File::options()
        .write(true)
        .truncate(true)
        .create(true)
        .open(state_file)
        .await?;
    let w = BufWriter::new(f.into_std().await);
    tokio::task::spawn_blocking(move || serde_yaml::to_writer(w, &list_state)).await??;
    Ok(())
}

async fn handle_list(
    list: &MailListConfig,
    state_file: &PathBuf,
    http_client: &reqwest::Client,
    url: &String,
    matrix_client: &Client,
    room_ids: &[OwnedRoomOrAliasId],
) -> anyhow::Result<()> {
    let list_state = load_list_state(state_file).await?;

    let rooms_f = room_ids.iter().map(|room_id| {
        matrix::ensure_room_joined(matrix_client, room_id)
            .map(move |res| res.with_context(|| format!("Failed to join Matrix room '{}'", room_id)))
    });
    let rooms = join_all(rooms_f)
        .await
        .into_iter()
        .flat_map(|room_res| match room_res {
            Err(err) => {
                warn!("{:#}", err);
                vec![]
            }
            Ok(room) => vec![room],
        })
        .collect::<Vec<_>>();
    if rooms.is_empty() {
        return Err(anyhow!("Failed to join all rooms for list '{}'; skipping", list.name));
    }

    let response = http_client
        .get(url)
        .send()
        .await
        .with_context(|| format!("Failed to fetch mail RSS feed from '{}'", url))
        .and_then(|response| {
            if !response.status().is_success() {
                Err(anyhow!(
                    "Failed to fetch mail RSS feed from '{}': server returned status {}",
                    url,
                    response.status().as_u16()
                ))
            } else {
                Ok(response)
            }
        })?;
    let body = response
        .text()
        .await
        .with_context(|| format!("Failed to decode RSS response body for '{}'", url))?;
    let mail_rss = tokio::task::spawn_blocking(move || quick_xml::de::from_str::<MailRss>(&body))
        .await?
        .with_context(|| format!("Failed to parse RSS feed for '{}'", url))?;
    let items = mail_rss
        .channel
        .items
        .into_iter()
        .rev()
        .skip_while(|item| item.pub_date.value <= list_state.last_pub_date)
        .collect::<Vec<_>>();

    for room in rooms {
        for item in &items {
            let msg =
                RoomMessageEventContent::text_markdown(format!("\\[{}\\] [{}]({}]", list.name, item.title, item.link));
            room.send(msg, None)
                .await
                .with_context(|| format!("Failed to send message to room '{}'", room.room_id()))?;
            save_list_state(
                ListState {
                    last_pub_date: item.pub_date.value,
                },
                state_file,
            )
            .await?;
        }
    }

    Ok(())
}

pub fn start_polling(config: MailArchiveConfig, matrix_client: Client) -> anyhow::Result<Vec<JoinHandle<()>>> {
    let http_client = reqwest::Client::builder()
        .user_agent(format!("{}/{}", env!("CARGO_PKG_NAME"), env!("CARGO_PKG_VERSION")))
        .gzip(true)
        .redirect(redirect::Policy::default())
        .timeout(Duration::from_secs(8))
        .build()?;

    Ok(config
        .lists
        .into_iter()
        .map(|list| {
            let room_ids = if list.rooms.is_empty() {
                &config.default_rooms
            } else {
                &list.rooms
            }
            .clone();
            let list = list.clone();
            let http_client = http_client.clone();
            let matrix_client = matrix_client.clone();
            let url = format!("https://www.mail-archive.com/{}/maillist.xml", list.name);
            let state_file = config.state_dir.join(format!("{}.state", list.name));
            let update_interval = Duration::from_secs(config.update_interval);

            tokio::spawn(async move {
                if !room_ids.is_empty() {
                    loop {
                        if let Err(err) =
                            handle_list(&list, &state_file, &http_client, &url, &matrix_client, &room_ids).await
                        {
                            warn!("{:#}", err);
                        }

                        sleep(update_interval).await;
                    }
                }
            })
        })
        .collect())
}

fn deser_rfc2616<'de, D>(deserializer: D) -> Result<DateTime<Utc>, D::Error>
where
    D: de::Deserializer<'de>,
{
    struct Rfc2616Visitor;

    impl<'de> de::Visitor<'de> for Rfc2616Visitor {
        type Value = DateTime<Utc>;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("an RFC2616-formatted datetime")
        }

        fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            dateparser::parse(v).map_err(E::custom)
        }
    }

    deserializer.deserialize_any(Rfc2616Visitor)
}

#[cfg(test)]
mod test {
    use std::{fs::File, io::BufReader};

    use super::MailRss;

    #[test]
    pub fn test_feed_deser() -> anyhow::Result<()> {
        let f = File::open(format!("{}/test-data/maillist.xml", env!("CARGO_MANIFEST_DIR")))?;
        let r = BufReader::new(f);
        let mail_rss = quick_xml::de::from_reader::<_, MailRss>(r)?;
        println!("{:#?}", mail_rss);
        Ok(())
    }
}