use std::collections::HashSet;
use std::io::SeekFrom;
use std::path::Path;
use std::time::Duration;

use anyhow::Result;
use json::JsonValue;
use rumqttc::{AsyncClient as MqttClient, EventLoop, LastWill, MqttOptions, Packet, SubscribeFilter};
use rumqttc::Event::Incoming;
use rumqttc::QoS;
use tokio::fs::{File, OpenOptions};
use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
use tokio::time::{Instant, sleep};

use crate::modules::ModuleContext;

use super::config;

pub async fn create_client(config: &config::Config, availability_topic: &str) -> Result<(MqttClient, EventLoop)> {
    let mut options = MqttOptions::new(&config.internal.stable_id, config.mqtt.host.to_owned(), config.mqtt.port);
    options.set_clean_session(true);
    options.set_keep_alive(Duration::from_secs(5));
    options.set_last_will(LastWill::new(availability_topic, "offline", QoS::AtLeastOnce, true));

    let (mqtt_client, event_loop) = MqttClient::new(options, 10);
    mqtt_client.publish(availability_topic, QoS::AtLeastOnce, true, "online").await?;

    Ok((mqtt_client, event_loop))
}

pub fn create_discovery_device_object(config: &config::Config) -> JsonValue {
    json::object! {
        "connections": if config.announce_mac_address {
            mac_address::get_mac_address().unwrap_or(None).map(|a| json::array![["mac", a.to_string()]]).unwrap_or(json::array![])
        } else {
            json::array![]
        },
        "name": config.display_name.as_str()
    }
}

pub struct OwnedTopicsService {
    file: File,
    old_topics: HashSet<String>,
}

impl OwnedTopicsService {
    pub async fn new(data_directory_path: &Path) -> Result<OwnedTopicsService> {
        let path = data_directory_path.join("owned_topics");
        let mut file = OpenOptions::new().write(true).read(true).create(true).open(path).await?;

        let mut content = String::new();
        file.read_to_string(&mut content).await?;

        let old_topics = content.split_terminator('\n').skip(1).map(|s| s.to_owned()).collect::<HashSet<_>>();

        Ok(OwnedTopicsService { file, old_topics })
    }

    pub async fn clear_old_and_save_new(mut self, mqtt_client: &MqttClient, new_topics: &HashSet<String>) -> Result<()> {
        let unused_topics = self.old_topics.difference(new_topics).map(|s| s.to_owned()).collect::<Vec<_>>();

        log::info!(
            "{} unused owned topics will be cleared. Now using {} owned topics.",
            unused_topics.len(),
            new_topics.len()
        );

        for topic in unused_topics.iter() {
            log::trace!("Clearing owned topic: {}", topic);

            // Deletes the retained message
            mqtt_client.publish(topic, QoS::AtLeastOnce, true, Vec::new()).await?;
        }

        let mut new_content = String::new();
        new_content.push_str("# DO NOT EDIT THIS FILE. It is automatically generated at each run of Hassliebe.\n");

        for topic in new_topics {
            new_content.push_str(topic);
            new_content.push('\n')
        }

        self.file.set_len(0).await?;
        self.file.seek(SeekFrom::Start(0)).await?;
        self.file.write_all(new_content.as_bytes()).await?;
        Ok(())
    }
}

#[derive(Debug, PartialEq, Eq)]
enum ConnectionState {
    NotConnected,
    FastRetrying { since: Instant },
    SlowRetrying,
    Connected,
}

const FAST_RETRYING_INTERVAL_MS: u64 = 500;
const FAST_RETRYING_LIMIT_SECONDS: u64 = 15;
const SLOW_RETRYING_INTERVAL_SECONDS: u64 = 5;

pub async fn start_communication(context: &ModuleContext<'_>, mut event_loop: EventLoop) -> Result<()> {
    log::info!("Connecting to MQTT broker at {}:{}", context.config.mqtt.host, context.config.mqtt.port);

    context
        .mqtt
        .client
        .subscribe_many(
            context
                .mqtt
                .message_handler_by_topic
                .keys()
                .map(|k| SubscribeFilter::new(k.to_owned(), QoS::AtLeastOnce)),
        )
        .await?;

    let mut connection_state = ConnectionState::NotConnected;

    loop {
        match connection_state {
            ConnectionState::FastRetrying { since } => {
                sleep(Duration::from_millis(FAST_RETRYING_INTERVAL_MS)).await;

                if since.elapsed().as_secs() >= FAST_RETRYING_LIMIT_SECONDS {
                    log::warn!(
                        "Could not fast-reconnect within {}s. Now retrying every {}s.",
                        FAST_RETRYING_LIMIT_SECONDS,
                        SLOW_RETRYING_INTERVAL_SECONDS
                    );
                    connection_state = ConnectionState::SlowRetrying;
                }
            }

            ConnectionState::SlowRetrying => {
                sleep(Duration::from_secs(SLOW_RETRYING_INTERVAL_SECONDS)).await;
            }

            _ => {}
        }

        let notification = event_loop.poll().await;

        match notification {
            Err(error) => {
                log::debug!("Connection error: {}", error);

                match connection_state {
                    ConnectionState::Connected => {
                        log::warn!("Connection lost. Trying to fast-reconnect…");
                        connection_state = ConnectionState::FastRetrying { since: Instant::now() };
                    }

                    ConnectionState::NotConnected => {
                        log::warn!("Connection failed. Retrying every {}s.", SLOW_RETRYING_INTERVAL_SECONDS);
                        connection_state = ConnectionState::SlowRetrying;
                    }

                    _ => {}
                }
            }

            Ok(event) => match event {
                Incoming(Packet::ConnAck(_)) => {
                    if connection_state == ConnectionState::NotConnected {
                        log::info!("Connection established")
                    } else {
                        log::info!("Connection restored")
                    }

                    connection_state = ConnectionState::Connected;
                }

                Incoming(Packet::Publish(message)) => {
                    let text = std::str::from_utf8(&message.payload)?;

                    if let Some(handler) = context.mqtt.message_handler_by_topic.get(message.topic.as_str()) {
                        handler(text)?;
                    }
                }

                _ => {}
            },
        }
    }
}