use std::sync::Arc;

use etcd_client::{Client, EventType, GetOptions, PutOptions, WatchOptions};
use tokio::sync::Mutex;
use tokio_stream::StreamExt;

/// etcd-backed config reader. Priority: etcd > env var > default.
pub struct EtcdConfig {
    client: Arc<Mutex<Client>>,
    prefix: String,
}

impl EtcdConfig {
    pub async fn connect(endpoints: Vec<String>, prefix: &str) -> Result<Self, String> {
        let client = Client::connect(endpoints, None)
            .await
            .map_err(|e| format!("etcd connect: {e}"))?;
        Ok(Self {
            client: Arc::new(Mutex::new(client)),
            prefix: prefix.to_string(),
        })
    }

    /// Get config value: etcd first, then env var, then default.
    pub async fn get(&self, key: &str, default: &str) -> String {
        let etcd_key = format!("{}config/{}", self.prefix, key);
        if let Ok(mut c) = self.client.try_lock() {
            if let Ok(resp) = c.get(etcd_key.as_str(), None).await {
                if let Some(kv) = resp.kvs().first() {
                    if let Ok(v) = kv.value_str() {
                        if !v.is_empty() {
                            tracing::info!(key, value = v, "config from etcd");
                            return v.to_string();
                        }
                    }
                }
            }
        }
        if let Ok(v) = std::env::var(key) {
            if !v.is_empty() {
                return v;
            }
        }
        default.to_string()
    }

    pub async fn get_parsed<T: std::str::FromStr>(&self, key: &str, default: T) -> T
    where
        T::Err: std::fmt::Display,
        T: std::fmt::Display,
    {
        let s = self.get(key, &default.to_string()).await;
        s.parse().unwrap_or(default)
    }

    /// Get the etcd client for use by ServiceRegistry.
    pub fn client(&self) -> Arc<Mutex<Client>> {
        self.client.clone()
    }

    /// Discover service instances registered under /{prefix}/services/{service_name}/.
    pub async fn discover_service(&self, service_name: &str) -> Result<Vec<String>, String> {
        let prefix = format!("{}services/{}/", self.prefix, service_name);
        let mut client = self.client.lock().await;
        let resp = client
            .get(prefix.as_str(), Some(GetOptions::new().with_prefix()))
            .await
            .map_err(|e| format!("etcd get {prefix}: {e}"))?;

        let mut addrs = Vec::new();
        for kv in resp.kvs() {
            if let Ok(value) = kv.value_str() {
                if let Ok(instance) = serde_json::from_str::<serde_json::Value>(value) {
                    if let Some(addr) = instance.get("addr").and_then(|v| v.as_str()) {
                        addrs.push(addr.to_string());
                    }
                }
            }
        }
        tracing::info!(
            service = service_name,
            count = addrs.len(),
            "discovered instances"
        );
        Ok(addrs)
    }

    /// Watch a service prefix for live join/leave events.
    ///
    /// Calls `on_up(addr)` when a new instance appears and `on_down(addr)`
    /// when one disappears. The watcher runs in a background task and
    /// automatically reconnects on failure.
    pub fn start_service_watcher(
        &self,
        service_name: &str,
        on_up: impl Fn(String) + Send + Sync + 'static,
        on_down: impl Fn(String) + Send + Sync + 'static,
    ) {
        let client = self.client.clone();
        let prefix = self.prefix.clone();
        let svc = service_name.to_string();
        let watch_prefix = format!("{}services/{}/", prefix, svc);

        let on_up = Arc::new(on_up);
        let on_down = Arc::new(on_down);

        tokio::spawn(async move {
            loop {
                let mut stream = {
                    let mut c = client.lock().await;
                    match c
                        .watch(
                            watch_prefix.as_str(),
                            Some(WatchOptions::new().with_prefix()),
                        )
                        .await
                    {
                        Ok(s) => s,
                        Err(e) => {
                            tracing::warn!(service = %svc, error = %e, "watch failed, retry in 3s");
                            tokio::time::sleep(std::time::Duration::from_secs(3)).await;
                            continue;
                        }
                    }
                };
                while let Some(resp) = stream.next().await {
                    let Ok(resp) = resp else { break };
                    for event in resp.events() {
                        let Some(kv) = event.kv() else { continue };
                        let raw = kv.value_str().unwrap_or_default();
                        let key = kv.key_str().unwrap_or_default();

                        // Parse JSON to extract the actual address
                        let addr = serde_json::from_str::<serde_json::Value>(raw)
                            .ok()
                            .and_then(|v| {
                                v.get("addr")
                                    .and_then(|a| a.as_str())
                                    .map(|s| s.to_string())
                            })
                            .unwrap_or_else(|| raw.to_string());

                        match event.event_type() {
                            EventType::Put => {
                                tracing::info!(service = %svc, key, addr, "service up");
                                on_up(addr);
                            }
                            EventType::Delete => {
                                tracing::info!(service = %svc, key, "service down");
                                on_down(addr);
                            }
                        }
                    }
                }
                tracing::warn!(service = %svc, "watch stream ended, restarting in 3s");
                tokio::time::sleep(std::time::Duration::from_secs(3)).await;
            }
        });
    }
}

/// Register this service instance in etcd.
pub struct ServiceRegistry {
    client: Arc<Mutex<Client>>,
    prefix: String,
}

impl ServiceRegistry {
    pub fn new(client: Arc<Mutex<Client>>, prefix: &str) -> Self {
        Self {
            client,
            prefix: prefix.to_string(),
        }
    }

    pub async fn register(&self, service_name: &str, addr: &str) -> Result<(), String> {
        let instance_id = uuid::Uuid::now_v7().to_string();
        let addr = addr.to_string();
        let key = format!("{}services/{}/{}", self.prefix, service_name, instance_id);

        let instance = serde_json::json!({
            "addr": &addr,
            "port": 0,
            "version": env!("CARGO_PKG_VERSION"),
        });
        let value = serde_json::to_string(&instance).map_err(|e| format!("json: {e}"))?;

        let lease = {
            let mut client = self.client.lock().await;
            client
                .lease_grant(60, None)
                .await
                .map_err(|e| format!("lease: {e}"))?
        };

        {
            let mut client = self.client.lock().await;
            let opts = PutOptions::new().with_lease(lease.id());
            client
                .put(key.clone(), value, Some(opts))
                .await
                .map_err(|e| format!("put: {e}"))?;
        }

        tracing::info!(service = service_name, instance = %instance_id, addr = %addr, "registered in etcd");

        let c = self.client.clone();
        let lease_id = lease.id();
        tokio::spawn(async move {
            let (mut keeper, mut stream) = {
                let mut client = c.lock().await;
                match client.lease_keep_alive(lease_id).await {
                    Ok(pair) => pair,
                    Err(e) => {
                        tracing::error!(lease_id, error = %e, "failed to start lease keepalive");
                        return;
                    }
                }
            };

            let mut interval = tokio::time::interval(std::time::Duration::from_secs(10));
            loop {
                interval.tick().await;
                if let Err(e) = keeper.keep_alive().await {
                    tracing::warn!(lease_id, error = %e, "lease keepalive failed");
                }
                let _ = stream.message().await;
            }
        });

        Ok(())
    }
}