use etcd_client::{GetOptions, WatchOptions};
use tokio_stream::StreamExt;
use uuid::Uuid;

use crate::error::{AppError, AppResult};
use crate::pb::{EmailClient, RepoClient};

use super::types::ServiceInstance;
use super::{EtcdRegistry, EtcdRegistryInner};

impl EtcdRegistry {
    pub async fn start_discovery(&self) -> AppResult<()> {
        self.load_initial("git").await?;
        self.load_initial("mail").await?;
        self.spawn_watch("git");
        self.spawn_watch("mail");
        Ok(())
    }

    async fn load_initial(&self, service: &str) -> AppResult<()> {
        let prefix = self.service_prefix(service);
        let resp = {
            let mut client = self.inner.client.lock().await;
            client
                .get(prefix.as_str(), Some(GetOptions::new().with_prefix()))
                .await
                .map_err(|e| AppError::Config(format!("etcd get {prefix} failed: {e}")))?
        };

        for kv in resp.kvs() {
            let key = kv.key_str().unwrap_or_default();
            let value = kv.value_str().unwrap_or_default();
            if let Ok(instance) = serde_json::from_str::<ServiceInstance>(value) {
                Self::upsert_instance(&self.inner, service, key, &instance);
            }
        }

        tracing::info!(
            service = service,
            prefix = prefix.as_str(),
            "etcd initial discovery complete"
        );
        Ok(())
    }

    fn spawn_watch(&self, service: &str) {
        let prefix = self.service_prefix(service);
        let inner = self.inner.clone();
        let service = service.to_string();

        tokio::spawn(async move {
            loop {
                match Self::watch_loop(&inner, &prefix, &service).await {
                    Ok(()) => break,
                    Err(e) => {
                        tracing::warn!(
                            service = service.as_str(),
                            error = %e,
                            "etcd watch disconnected, retrying in 3s"
                        );
                        tokio::time::sleep(std::time::Duration::from_secs(3)).await;
                    }
                }
            }
        });
    }

    async fn watch_loop(inner: &EtcdRegistryInner, prefix: &str, service: &str) -> AppResult<()> {
        let (mut watcher, mut stream) = {
            let mut client = inner.client.lock().await;
            client
                .watch(prefix, Some(WatchOptions::new().with_prefix()))
                .await
                .map_err(|e| AppError::Config(format!("etcd watch {prefix} failed: {e}")))?
        };

        let _keep = &mut watcher;

        while let Some(resp) = stream.next().await {
            let resp =
                resp.map_err(|e| AppError::Config(format!("etcd watch stream error: {e}")))?;

            for event in resp.events() {
                let Some(kv) = event.kv() else { continue };
                let key = kv.key_str().unwrap_or_default();

                match event.event_type() {
                    etcd_client::EventType::Put => {
                        let value = kv.value_str().unwrap_or_default();
                        if let Ok(instance) = serde_json::from_str::<ServiceInstance>(value) {
                            Self::upsert_instance(inner, service, key, &instance);
                            tracing::info!(service = service, key = key, "etcd service upserted");
                        }
                    }
                    etcd_client::EventType::Delete => {
                        Self::remove_instance(inner, service, key);
                        tracing::info!(service = service, key = key, "etcd service removed");
                    }
                }
            }
        }
        Ok(())
    }

    pub(crate) fn service_prefix(&self, service: &str) -> String {
        format!("{}services/{service}/", self.inner.key_prefix)
    }

    fn extract_id_from_key(key: &str) -> Option<Uuid> {
        key.rsplit('/').next()?.parse().ok()
    }

    fn upsert_instance(
        inner: &EtcdRegistryInner,
        service: &str,
        key: &str,
        instance: &ServiceInstance,
    ) {
        let Some(node_id) = Self::extract_id_from_key(key) else {
            tracing::warn!(key = key, "etcd key has no valid UUID suffix");
            return;
        };
        let addr = instance.addr.clone();

        match service {
            "git" => match RepoClient::lazy_connect(&addr) {
                Ok(client) => {
                    inner.git_nodes.insert(node_id, client);
                }
                Err(e) => {
                    tracing::error!(key = key, addr = addr.as_str(), error = %e, "git client connect failed");
                }
            },
            "mail" => match EmailClient::lazy_connect(&addr) {
                Ok(client) => {
                    inner.mail_nodes.insert(node_id, client);
                }
                Err(e) => {
                    tracing::error!(key = key, addr = addr.as_str(), error = %e, "mail client connect failed");
                }
            },
            _ => {}
        }
    }

    fn remove_instance(inner: &EtcdRegistryInner, service: &str, key: &str) {
        let Some(node_id) = Self::extract_id_from_key(key) else {
            return;
        };
        match service {
            "git" => {
                inner.git_nodes.remove(&node_id);
            }
            "mail" => {
                inner.mail_nodes.remove(&node_id);
            }
            _ => {}
        }
    }
}