mod types;

use types::*;

use reqwest::{Client, Url};
use tokio::signal::unix::{signal, SignalKind};

const BOT_URL: &str = "https://api.telegram.org/bot";
/// Command to search for in a message text
const COMMAND: &str = "/xkcd";
/// Length of the command substring
const CMD_LEN: usize = COMMAND.len();
/// Long polling timeout in seconds
const POLL_TIMEOUT: &str = "300";
/// Update types to receive (filtered out on tg backend)
const POLL_TYPES: &str = r#"["message"]"#;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let cfg = {
        let token = std::env::var("BOT_TOKEN").expect("invalid BOT_TOKEN env var value");
        let client = Client::new();

        init_cmds(&client, &token)
            .await
            .expect("could not make request to API");

        Config {
            client,
            upd_url: Url::parse(&format!("{BOT_URL}{token}/getUpdates"))
                .unwrap()
                .into(),
            send_url: Url::parse(&format!("{BOT_URL}{token}/sendPhoto"))
                .unwrap()
                .into(),
        }
    };

    let mut s = State { offset: 0 };

    let mut sigint = signal(SignalKind::interrupt())?;
    let mut sigterm = signal(SignalKind::terminate())?;

    loop {
        tokio::select! {
            _ = sigint.recv() => {
                break;
            }
            _ = sigterm.recv() => {
                break;
            }
            out = handler(&cfg, &mut s) => {
                match out {
                    Ok(_) => {}
                    Err(e) => {
                        eprintln!("[handler] {:?}", e);
                    }
                }
            }
        }
    }

    Ok(())
}

async fn init_cmds(client: &Client, token: &str) -> Result<(), reqwest::Error> {
    client
        .get(format!("{BOT_URL}{token}/setMyCommands"))
        .query(&[(
            "commands",
            serde_json::json!([
                {
                    "command": COMMAND[1..], // cmd name without leading slash
                    "description": "Get XKCD comic by id",
                }
            ])
            .to_string(),
        )])
        .send()
        .await?
        .error_for_status()?;

    Ok(())
}

async fn handler(cfg: &Config, s: &mut State) -> Result<(), reqwest::Error> {
    let mut updates = cfg
        .client
        .get((*cfg.upd_url).clone())
        .query(&[
            ("offset", s.offset.to_string().as_str()),
            ("timeout", POLL_TIMEOUT),
            ("allowed_updates", POLL_TYPES),
        ])
        .send()
        .await?
        .json::<TgResponse>()
        .await?
        .result;

    updates
        .iter_mut()
        .filter_map(|u| {
            u.message.take().and_then(|mut msg| {
                msg.text.take().and_then(|text| {
                    // starts with our command
                    if text.get(..CMD_LEN)? == COMMAND
                        // check space or @ after cmd name
                        // to ensure that our command is
                        // not a part of any other cmd
                        && [" ", "@"].contains(&text.get(CMD_LEN..CMD_LEN + 1)?)
                    {
                        let mut args = text.split_whitespace();
                        args.next(); // skip command name
                        match args.next()? {
                            "ru" => {
                                let comic_id = args.next()?.parse::<u16>().ok()?;
                                Some((msg, format!("https://xkcd.ru/{}/?json=true", comic_id)))
                            }
                            "en" => {
                                let comic_id = args.next()?.parse::<u16>().ok()?;
                                Some((msg, format!("https://xkcd.com/{}/info.0.json", comic_id)))
                            }
                            comic_id => {
                                let comic_id = comic_id.parse::<u16>().ok()?;
                                Some((msg, format!("https://xkcd.com/{}/info.0.json", comic_id)))
                            }
                        }
                    } else {
                        None
                    }
                })
            })
        })
        .for_each(|(msg, url)| {
            tokio::spawn(send_comic(cfg.clone(), msg, url));
        });

    if let Some(u) = updates.last() {
        s.offset = u.update_id + 1;
    }

    Ok(())
}

async fn send_comic(cfg: Config, msg: TgMessage, url: String) -> Result<(), reqwest::Error> {
    let info = cfg.client.get(url).send().await?.json::<XkcdInfo>().await?;

    cfg.client
        .post((*cfg.send_url).clone())
        .form(&[
            ("chat_id", msg.chat.id.to_string()),
            (
                "message_thread_id",
                msg.thread
                    .map(|t| t.to_string())
                    .unwrap_or("null".to_owned()),
            ),
            ("photo", info.img),
            ("caption", info.alt),
        ])
        .send()
        .await?;

    Ok(())
}