//! [Telegram bot](https://core.telegram.org/bots/api) service able to receive and send messages.

use crate::consts::USER_AGENT;
use crate::message::{Message, Type};
use crate::value::Value;
use crate::{threading, Result};
use chrono::{DateTime, Utc};
use crossbeam_channel::Sender;
use failure::format_err;
use log::{debug, error};
use regex::Regex;
use reqwest::header::{HeaderMap, HeaderValue};
use reqwest::Client;
use serde::de::DeserializeOwned;
use serde::{Deserialize, Serialize};
use serde_json::json;
use std::fmt::Debug;
use std::thread;
use std::time::Duration;

const TIMEOUT: u32 = 60;

#[derive(Deserialize, Debug, Clone)]
pub struct Settings {
    token: String,
}

/// Spawn the service.
pub fn spawn(service_id: &str, settings: &Settings, tx: &Sender<Message>) -> Result<Vec<Sender<Message>>> {
    spawn_producer(Context::new(service_id, &settings.token)?, tx)?;
    Ok(vec![spawn_consumer(Context::new(service_id, &settings.token)?)?])
}

struct Context {
    client: Client,
    service_id: String,
    token: String,
}

impl Context {
    fn new(service_id: &str, token: &str) -> Result<Self> {
        let mut headers = HeaderMap::new();
        headers.insert(reqwest::header::USER_AGENT, HeaderValue::from_static(USER_AGENT));

        Ok(Self {
            client: reqwest::Client::builder()
                .gzip(true)
                .timeout(Duration::from_secs((TIMEOUT + 1).into()))
                .default_headers(headers)
                .build()?,
            service_id: service_id.into(),
            token: token.into(),
        })
    }
}

/// Spawn thread that listens for Telegram updates and produces reading messages.
fn spawn_producer(context: Context, tx: &Sender<Message>) -> Result<()> {
    let tx = tx.clone();

    threading::spawn(
        format!("my-iot::telegram::producer::{}", &context.service_id),
        move || {
            let mut offset: Option<i64> = None;
            loop {
                match get_updates(&context, offset) {
                    Ok(updates) => {
                        for update in updates.iter() {
                            offset = offset.max(Some(update.update_id + 1));
                            send_readings(&context, &tx, &update).unwrap();
                        }
                        debug!("{}: next offset: {:?}", &context.service_id, offset);
                    }
                    Err(error) => {
                        log::error!("Telegram has failed: {}", error);
                        thread::sleep(Duration::from_millis(60000)); // FIXME: something smarter.
                    }
                }
            }
        },
    )?;

    Ok(())
}

/// Send reading messages from the provided Telegram update.
fn send_readings(context: &Context, tx: &Sender<Message>, update: &TelegramUpdate) -> Result<()> {
    debug!("{}: {:?}", &context.service_id, &update);

    if let Some(ref message) = update.message {
        if let Some(ref text) = message.text {
            tx.send(Message::new(
                Type::OneOff,
                format!("{}::{}::message", &context.service_id, message.chat.id),
                Value::Text(text.into()),
                message.date.into(),
            ))?;
        }
    }

    Ok(())
}

/// Spawn thread that listens for `Control` messages and communicates back to Telegram.
fn spawn_consumer(context: Context) -> Result<Sender<Message>> {
    let message_regex = Regex::new(&format!(
        r"^{}::(?P<chat_id>\-?\d+)::(?P<sensor>\w+)",
        &context.service_id,
    ))?;
    let (tx, rx) = crossbeam_channel::unbounded::<Message>();

    threading::spawn(
        format!("my-iot::telegram::consumer::{}", &context.service_id),
        move || {
            for message in rx {
                if message.type_ != Type::Control {
                    continue;
                }
                let (chat_id, sensor) = match message_regex.captures(&message.reading.sensor) {
                    Some(captures) => (captures.get(1).unwrap().as_str(), captures.get(2).unwrap().as_str()),
                    None => continue,
                };
                let chat_id: TelegramChatId = chat_id.into();
                let error = match message.reading.value {
                    Value::Text(ref text) if sensor == "message" => send_message(&context, chat_id, text).err(),
                    Value::ImageUrl(ref url) if sensor == "photo" => send_photo(&context, chat_id, url).err(),
                    Value::ImageUrl(ref url) if sensor == "animation" => send_animation(&context, chat_id, url).err(),
                    value => Some(format_err!("cannot send {:?} to {}", &value, &message.reading.sensor)),
                };
                if let Some(error) = error {
                    error!("{:?}", error);
                }
            }
            unreachable!();
        },
    )?;

    Ok(tx)
}

/// Call [Telegram Bot API](https://core.telegram.org/bots/api) method.
fn call_api<P: Serialize + Debug + ?Sized, R: DeserializeOwned>(
    context: &Context,
    method: &str,
    parameters: &P,
) -> Result<R> {
    debug!("{}({:?})", &method, parameters);
    context
        .client
        .get(&format!("https://api.telegram.org/bot{}/{}", &context.token, method))
        .json(parameters)
        .send()?
        .json::<TelegramResponse<R>>()
        .map_err(Into::into)
        .and_then(|response| {
            if response.ok {
                Ok(response.result.unwrap())
            } else {
                Err(format_err!("{}", response.description.unwrap()))
            }
        })
}

/// <https://core.telegram.org/bots/api#getupdates>
fn get_updates(context: &Context, offset: Option<i64>) -> Result<Vec<TelegramUpdate>> {
    call_api(
        context,
        "getUpdates",
        &json!({
            "offset": offset,
            "limit": null,
            "timeout": TIMEOUT,
            "allowed_updates": ["message"],
        }),
    )
}

/// <https://core.telegram.org/bots/api#sendmessage>
fn send_message<T: AsRef<str>>(context: &Context, chat_id: TelegramChatId, text: T) -> Result<TelegramMessage> {
    call_api(
        context,
        "sendMessage",
        &json!({
            "chat_id": chat_id,
            "text": text.as_ref(),
        }),
    )
}

/// <https://core.telegram.org/bots/api#sendphoto>
fn send_photo<P: Into<TelegramFile>>(context: &Context, chat_id: TelegramChatId, photo: P) -> Result<TelegramMessage> {
    call_api(
        context,
        "sendPhoto",
        &json!({
            "chat_id": chat_id,
            "photo": photo.into(),
        }),
    )
}

/// <https://core.telegram.org/bots/api#sendanimation>
fn send_animation<A: Into<TelegramFile>>(
    context: &Context,
    chat_id: TelegramChatId,
    animation: A,
) -> Result<TelegramMessage> {
    call_api(
        context,
        "sendAnimation",
        &json!({
            "chat_id": chat_id,
            "animation": animation.into(),
        }),
    )
}

#[derive(Serialize, Debug)]
#[serde(untagged)]
enum TelegramChatId {
    UniqueId(i64),
    Username(String),
}

impl From<&str> for TelegramChatId {
    fn from(string: &str) -> Self {
        match string.parse::<i64>() {
            Ok(chat_id) => TelegramChatId::UniqueId(chat_id),
            Err(_) => TelegramChatId::Username(string.into()),
        }
    }
}

#[derive(Serialize, Debug)]
#[serde(untagged)]
enum TelegramFile {
    Url(String),
}

impl From<&String> for TelegramFile {
    fn from(string: &String) -> Self {
        TelegramFile::Url(string.into())
    }
}

/// <https://core.telegram.org/bots/api#making-requests>
#[derive(Deserialize, Debug)]
struct TelegramResponse<T> {
    ok: bool,
    description: Option<String>,
    result: Option<T>,
}

#[derive(Deserialize, Debug)]
struct TelegramUpdate {
    update_id: i64,
    message: Option<TelegramMessage>,
}

/// <https://core.telegram.org/bots/api#message>
#[derive(Deserialize, Debug)]
struct TelegramMessage {
    message_id: i64,

    #[serde(deserialize_with = "chrono::serde::ts_seconds::deserialize")]
    date: DateTime<Utc>,

    chat: TelegramChat,
    text: Option<String>,
}

/// <https://core.telegram.org/bots/api#chat>
#[derive(Deserialize, Debug)]
struct TelegramChat {
    id: i64,
}