//! NATS client — single connection shared across MessageProducer, workers, and pubsub.
//!
//! Uses Core NATS for real-time broadcast (fan-out) and JetStream for message
//! persistence (durable consumers). Replaces Redis Pub/Sub + Redis Streams.

use std::sync::Arc;
use std::time::Duration;

use async_nats::jetstream;
use config::AppConfig;

pub struct NatsClient {
    pub client: async_nats::Client,
    pub jetstream: jetstream::Context,
    stream_name: String,
    connected: Arc<std::sync::atomic::AtomicBool>,
}

impl NatsClient {
    pub async fn connect(config: &AppConfig) -> Option<Self> {
        let url = config.nats_url()?;
        let token = config.nats_token()?;

        let opts = async_nats::ConnectOptions::with_token(token)
            .retry_on_initial_connect()
            .connection_timeout(Duration::from_secs(10))
            .reconnect_delay_callback(|attempts| {
                let ms = 100 * 2u64.saturating_pow(attempts as u32);
                Duration::from_millis(ms.min(30_000))
            })
            .event_callback(|event| async move {
                match event {
                    async_nats::Event::Connected => {
                        tracing::info!("NATS connected");
                    }
                    async_nats::Event::Disconnected => {
                        tracing::warn!("NATS disconnected, reconnecting...");
                    }
                    async_nats::Event::ServerError(e) => {
                        tracing::warn!(error = %e, "NATS server error");
                    }
                    _ => {}
                }
            });

        match opts.connect(&url).await {
            Ok(client) => {
                let connected = Arc::new(std::sync::atomic::AtomicBool::new(true));
                let connected_clone = connected.clone();

                // Track connection state for health checks
                let client_clone = client.clone();
                tokio::spawn(async move {
                    let mut attempts: u64 = 0;
                    loop {
                        tokio::time::sleep(Duration::from_secs(5)).await;
                        let was = connected_clone.load(std::sync::atomic::Ordering::SeqCst);
                        let is = client_clone.connection_state()
                            == async_nats::connection::State::Connected;
                        if was != is {
                            connected_clone.store(is, std::sync::atomic::Ordering::SeqCst);
                            if is {
                                attempts = 0;
                            }
                        }
                        if !is {
                            attempts += 1;
                            if attempts > 12 {
                                tracing::error!("NATS disconnected for {}s", attempts * 5);
                            }
                        }
                    }
                });

                let jetstream = jetstream::new(client.clone());
                let stream_name = config.nats_stream_name();

                let nats = Self {
                    client,
                    jetstream,
                    stream_name,
                    connected,
                };

                if let Err(e) = nats.ensure_stream(config).await {
                    tracing::warn!(error = %e, "JetStream stream init failed");
                } else {
                    tracing::info!(stream = %nats.stream_name, "JetStream stream ready");
                }

                tracing::info!(url = %url, "NATS connected");
                Some(nats)
            }
            Err(e) => {
                tracing::warn!(error = %e, url = %url, "NATS connect failed — running without NATS");
                None
            }
        }
    }

    /// Create or verify the JetStream stream for room message persistence.
    pub async fn ensure_stream(&self, config: &AppConfig) -> anyhow::Result<()> {
        let stream_config = jetstream::stream::Config {
            name: self.stream_name.clone(),
            subjects: vec![
                "room.message.>".to_string(),
                "room.chunk.>".to_string(),
                "chat.message.>".to_string(),
                "chat.chunk.>".to_string(),
                "chat.subagent.chunk.>".to_string(),
            ],
            retention: jetstream::stream::RetentionPolicy::Interest,
            max_age: Duration::from_secs(config.nats_max_age_secs()),
            storage: jetstream::stream::StorageType::File,
            max_messages_per_subject: 100_000,
            ..Default::default()
        };

        self.jetstream
            .get_or_create_stream(stream_config)
            .await
            .map_err(|e| anyhow::anyhow!("JetStream stream create failed: {}", e))?;

        Ok(())
    }

    pub fn is_connected(&self) -> bool {
        self.connected.load(std::sync::atomic::Ordering::SeqCst)
    }

    pub fn stream_name(&self) -> &str {
        &self.stream_name
    }

    /// Publish to core NATS for real-time broadcast. Fire-and-forget.
    pub async fn core_publish(&self, subject: String, payload: Vec<u8>) {
        if let Err(e) = self.client.publish(subject.clone(), payload.into()).await {
            tracing::warn!(subject = %subject, error = %e, "NATS core publish failed");
        }
    }

    /// Publish to JetStream and await the publish acknowledgement.
    /// Returns the stream sequence number, or 0 on failure.
    pub async fn jetstream_publish(
        &self,
        subject: String,
        payload: Vec<u8>,
    ) -> anyhow::Result<u64> {
        let ack_future = self
            .jetstream
            .publish(subject.clone(), payload.into())
            .await
            .map_err(|e| anyhow::anyhow!("JetStream publish failed: {}", e))?;

        let ack = ack_future
            .await
            .map_err(|e| anyhow::anyhow!("JetStream publish ack failed: {}", e))?;

        Ok(ack.sequence)
    }

    /// Create a core NATS subscription. Returns a subscriber receiver.
    pub async fn subscribe(&self, subject: &str) -> anyhow::Result<async_nats::Subscriber> {
        self.client
            .subscribe(subject.to_string())
            .await
            .map_err(|e| anyhow::anyhow!("NATS subscribe failed: {}", e))
    }

    /// Create or get an ephemeral JetStream push consumer for broadcast delivery.
    /// Returns a message stream that will receive messages published to the subject.
    pub async fn consumer_messages(
        &self,
        durable: &str,
        filter_subject: &str,
        config: &AppConfig,
    ) -> anyhow::Result<async_nats::jetstream::consumer::pull::Stream> {
        let stream = self
            .jetstream
            .get_stream(&self.stream_name)
            .await
            .map_err(|e| anyhow::anyhow!("JetStream get stream failed: {}", e))?;

        let pull_config = async_nats::jetstream::consumer::pull::Config {
            durable_name: Some(durable.to_string()),
            filter_subject: filter_subject.to_string(),
            max_deliver: config.nats_max_deliver(),
            ack_wait: Duration::from_secs(config.nats_ack_wait_secs()),
            max_ack_pending: config.nats_buffer_size() as i64,
            ..Default::default()
        };

        let consumer = stream
            .get_or_create_consumer(durable, pull_config)
            .await
            .map_err(|e| anyhow::anyhow!("JetStream consumer create failed: {}", e))?;

        consumer
            .messages()
            .await
            .map_err(|e| anyhow::anyhow!("JetStream consumer messages failed: {}", e))
    }
}